- Email: [email protected]
Bacteriuria detection with a urine dipstick applied to incontinence pads of nursing home residents
Bacteriuria Detection
with
A
Urine
Dipstick Applied TO Incontinence Pads OF Nursing Home Residents Susan J. Midthun, MS, RN, Ruth A. Paur, MS, MJ, ASCP, Glenda Lindseth, PhD, RN, RD, and Serge P. Von Duvillard, PhD, FASCM
T
he purpose of this study was to evaluate a new method of initial on-site evaluation of bacteriuria in an incontinent nursing home population. Nitrite and a composite of nitrite and/or leukocyte esterase results of the new method were compared with clean-catch urine culture results of each participant to determine sensitivity, specificity, positive and negative predictive values, and efficiency. These findings were compared with results of the traditional dipstick urinalysis for bacteriuria assessment. The new method was as effective as the traditional method in assessing both the presence and absence of bacteriuria. Results of this study indicate the new dipstick/pad method may assist in the assessment of bacteriuria in incontinent nursing home residents. (Geriatr Nurs 2003;24:206-9)
Elders who are incontinent and confused pose a special challenge for determining the presence of a urinary tract infection (UTI). They may exhibit some UTI symptoms chronically and may not be able to communicate the presence of others, such as pain or temperature.1 Urine specimens may be difficult to obtain in this population, and catheterization itself may cause a UTI.2 A method to assess bacteriuria using pad urine would be easier and safer for these at-risk people. In the laboratory, a urine dipstick is immersed in a clean-catch urine specimen for initial evaluation of bacteriuria. The dipstick detects nitrite and leukocyte esterase. Nitrite is present when certain types of bacteria reduce dietary nitrate in the urine to nitrite. Leukocyte esterase is a component of white blood cells (WBCs), which often accompany bacteriuria.3 Assessment of bacteriuria and pyuria using urine from pads has reported varying results.4-9 A urine dipstick pressed into a wet incontinence pad of an elderly nursing home resident may be an effective method to assess bacteriuria. This method would be easy, 206
safe, and inexpensive in the initial evaluation of a UTI. It would allow simple laboratory data to be obtained without a laboratory facility, add objective data to the clinical picture, and assist in assessment and management of UTIs in the nursing home resident. The purpose of this study, therefore, was to evaluate a new method (dipstick/pad = dipstick pressed onto a recently wet incontinence pad) of initial on-site evaluation of bacteriuria in an incontinent nursing home population. METHOD A convenience sample of 98 residents was selected from lists generated by 6 nursing homes of incontinent residents who were antibiotic free for 14 days, had no recent record of vaginal discharge, and who could give clean-catch urine specimens. Informed consent was obtained from the residents or their responsible parties. Six to 10 participants per night were tested as follows. At the beginning of the night shift (22:00), 2 research assistants, each of whom had been given 1-hour instruction and practice in dipstick analysis, cleaned the urethral Geriatric Nursing
Volume 24
Number 4
area of the participant with soap and water. A urine incontinence pad (SCA Hygiene, Eddystone, Pa.) was applied. The pad was constructed of wood pulp and a superabsorbent polymer. Participants were monitored hourly, and wet pads were removed immediately and tested. Pads that were grossly contaminated with feces or contained less than 50 mL of urine by weight were not included in the study. A Chemstrip 10™ (Roche Diagnostics, Indianapolis, Ind.) dipstick was pressed onto the wettest part of the pad for 10 seconds. Timing of the nitrite and leukocyte esterase tests began immediately after dipstick removal and results read according to the color chart found on the dipstick bottle per the manufacturer’s guidelines. Leukocyte esterase results were recorded as negative, trace, 1+, or 2+. Nitrite results were positive or negative and recorded as such. Based on voiding habits, a clean-catch specimen was obtained in the early morning between 5 and 7:30 by the research assistants. The participant’s urethral area again was cleaned with soap and water. The resident voided into a new bedpan, urinal, or a hat placed in a toilet. The specimen then was poured into a sterile container. The clean-catch specimen was coded immediately and placed on ice in a cooler. Specimens were transported to the pathology department of the University of North Dakota School of Medicine and tested 3 to 8 hours after the participant voided. Urine analysis was performed in the following manner: a dipstick was immersed in the urine specimen and read per manufacturer’s instructions (dipstick/ua). Results were recorded in the same manner as the dipstick/pad method. Ten mL of the urine specimen then was centrifuged for 5 minutes at 400 x g. Nine mL of the supernatant was removed, and the sediment suspended in the remaining 1 mL sample. A drop of this suspension was placed on a slide and viewed under 450 X light microscopy. Results of 10 or less WBCs per high-powered field were considered negative, and more than 10 WBCs per high powered field positive for pyuria. Urine cultures were conducted on all samples. A 0.001mL calibrated bacteriological loop was used to inoculate the urine specimen onto MacConkey plates and tryptic soy agar plates that contained 5% sheep blood. Both plates were incubated at 37º C in ambient atmosphere for 48 hours. A culture result was considered positive if the urine grew one colony type (more than 100,000 colony-forming units per mL) within 48 hours. Background contaminating flora less than 25,000 colony-forming units per mL was not considered pathogenic. A single colony type of 50,000 colony-forming units per mL also was considered negative to adhere to the current recommendation of a positive urine culture.10 Nitrite and leukocyte esterase results may be affected by some antibiotics, nitrofurantoin, vitamin C (more than 500 mg/day), and phenazopyridine.11,12 These medications were not prescribed for participants in this study. Albumin more than 500 mg per mL is stated to affect July—August 2003
leukocyte esterase test results.11 No participant’s urine contained this amount of protein. No participant was acutely symptomatic for a UTI. The dipstick/pad and dipstick/ua methods were compared with culture results of the clean-catch urine specimen to determine sensitivity, specificity, positive and negative predictive values, and efficiency. Nitrite results were compared with culture results in bacteriuria detection. Because a composite of leukocyte esterase and nitrite has been shown to increase sensitivity of bacteriuria detection,13,14 2 composites of nitrite and/or leukocyte esterase results were compared with culture results for the detection of bacteriuria. The first consisted of a positive nitrite and/or 1+ or 2+ leukocyte esterase as indicative for bacteriuria. The second consisted of a positive nitrite and/or trace, 1+, or 2+ leukocyte esterase as indicative for bacteriuria. The following formulas for determining sensitivity, specificity, positive and negative predictive values, and efficiency of the dipstick/pad and dipstick/ua methods were used based on positive (pos) and negative (neg) results.15 Sensitivity = true pos/(true pos + false neg) X 100 Specificity = true neg/(true neg + false pos) X 100 Positive Predictive Value (PPV) = true pos/(true pos + false pos) X 100 Negative Predictive Value (NPV) = true neg/(true neg + false neg) X 100 Efficiency = true pos + true neg/(true pos + false pos + true neg + false neg) X 100
R E S U LT S In this study, 144 residents or their responsible parties gave consent for their participation. Forty-six were removed for reasons that included initiation of antibiotic therapy, death, or inability to give an incontinence pad containing 50 mL of urine or a 10 mL by clean-catch urine sample. A total of 98 residents were included in the study, the majority of whom were women (83.7%). Ages of the participants ranged from 64 to 101, with a mean age of 86. Urine specimens testing positive for bacteriuria were found in 27 or 27.6% of the sample. Of the study specimens positive for bacteriuria, 14 or 51.9% had accompanying pyuria of more than 10 WBCs per high powered field. The total number of pyuric specimens was 19 (19.4%), and 14 of these (73.7%) were bacteriuric. Nitrite results indicative for bacteriuria for both methods are shown in Table 1. These findings reflect other studies that reported pad urine as effective as clean-catch, suprapubic aspiration, or catheterized urine in bacteriuria detection.4,7,9 Table 2 identifies a composite of either positive nitrite and/or 1+ or 2+ leukocyte esterase as indicative for bacteriuria for both methods. Table 3 identifies a composite of either positive nitrite and/or any positive leukocyte esterase result (trace, 1+, or 2+) as indicative for bacteriuria for both methods. Sensitivity of both methods improved, whereas specificity decreased. 207
Table 1. Comparison of nitrite results as positive with culture results Dipstick/pad Positive
Negative
Dipstick/ua Total
Positive
Negative
Total
27 71 98
18 1 19
9 70 79
27 71 98
Culture Results Positive Negative Total
19 2 21
8 69 77
Dipstick/pad: Sensitivity 70.4%, Specificity 97.2%, PPV 90.5%, NPV 89.6%, Efficiency 89.8% Dipstick/ua: Sensitivity 66.7%, Specificity 98.6%, PPV 94.7%, NPV 88.6%, Efficiency 89.8%
Table 2. Comparison of nitrite and/or 1+ or 2+ leukocyte esterase results as positive with culture results Dipstick/pad Positive
Dipstick/ua
Negative
Total
Positive
Negative
Total
Culture Results Positive
21
6
27
22
5
27
Negative
17
54
71
10
61
71
Total
38
60
98
32
66
98
Dipstick/pad: Sensitivity 77.8%, Specificity 76.1%, PPV 56.2%, NPV 90.0%, Efficiency 76.5% Dipstick/ua: Sensitivity 81.5%, Specificity 85.9%, PPV 68.8%, NPV 92.4%, Efficiency 84.7%
DISCUSSION Negative results of the dipstick/pad method that included trace leukocyte esterase as positive (Table 3) were a good indication of no bacteriuria. However 73% of the positive results (30 of 71) were false. Positive results of the dipstick/pad method using nitrite alone were a very good indication of bacteriuric people. However 30% (n = 8) of bacteriuric specimens were missed in this application because of false negative results. PPV and NPV also were calculated for both methods. The PPV measures the probability that a positive result indicates the presence of the disease; the NPV measures the probability that a negative result indicates the absence of a disease.15 Predictive values, unlike sensitivity and specificity, take into consideration the prevalence of a disease in the population studied.15 Looking at these values, nitrite results alone of both methods had the best outcomes. Approximately 90% (19 of 21) positive results were true positive, and about 90% (69 of 77) results were true negative. Efficiency, the percentage of correct results per total sample population, also indicated nitrite results alone as the most accurate in identifying abacteriuria and bacteriuria. In both methods, 90% of people were correctly identified as positive or negative. The dipstick/pad method, done at the nursing home, was as effective as the commonly used laboratory test (dipstick/ua) in assessment of bacteriuria in the incontinent nursing home population.
208
L I M I TAT I O N S Results depend on the population studied.16,17 Dipstick/pad results for bacteriuria identification of symptomatic, incontinent people who are unable to give urine samples may not be identical to results of this study. Also, 92% of bacteria found in this study were nitrite producers. Although most bacteria found in other nursing home studies were nitrite producers, the rate varied.18-20 Results of the dipstick/pad method also may vary accordingly. C O N C L U S I O N S A N D R E C O M M E N D AT I O N S The nitrite results of the dipstick/pad method, done at the nursing home, were as effective as nitrite results of the dipstick/ua test, a commonly used laboratory method, in the assessment of both the presence and absence of bacteriuria. A quick, simple, noninvasive, and inexpensive method of initial assessment of bacteriuria used for incontinent nursing home residents would improve outcomes for this vulnerable population. For acutely symptomatic people identified as bacteriuric by positive nitrite results, intensified nursing interventions could be initiated, such as encouraging fluids and monitoring for increasing symptoms and possible further urinalysis. Results of these interventions could be monitored using the pad method as well. This test alone would not justify antibiotic treatment. Used in this context, a 10% error would seem acceptable. Using negative results,
Geriatric Nursing
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Number 4
Table 3. Comparison of nitrite and/or trace, 1+, or 2+ leukocyte esterase results as positive with culture results Dipstick/pad Positive
Negative
Dipstick/ua Total
Positive
Negative
Total
Culture Results Positive
26
1
27
26
1
27
Negative
30
41
71
16
55
71
Total
56
42
98
42
56
98
Dipstick/pad: Sensitivity 96.3%, Specificity 57.8%, PPV 46.4%, NPV 97.6%, Efficiency 68.4% Dipstick/ua: Sensitivity 96.3%, Specificity 77.5%, PPV 61.9%, NPV 98.2%, Efficiency 82.7%
a method that identified the absence of bacteriuria in acutely symptomatic people would decrease cost of unnecessary further testing and potential antibiotic treatment and focus scarce resources on more effective and less hazardous means of relief. Regarding the 1 in 10 false negative people, the clinical picture becomes especially important. Further studies may improve the dipstick/pad method by identifying those people who may be at risk for false negative results. These may include residents with nausea, vomiting, or diarrhea, possibly contributing to a lack of dietary nitrate, or urine “dribblers” who are unable to retain urine long enough for bacteria to convert nitrate to nitrite. Studies of a second dipstick/pad test the following night may show improvement in both PPV and NPV of this method. For asymptomatic people, bacteriuria screening is not recommended because it is not considered necessary to treat this condition. UTIs, however, are the major nosocomial nursing home infection, and nurses’ hands may be the primary mode of transmission.21 In the interest of infection control, nurses would seem justified in monitoring the presence or absence of all types of bacteriuria in the nursing home population. REFERENCES 1. Castle S, Norman D, Yeh M, Miller D, Yoshikawa T. Fever response in elderly nursing home residents: are the older truly colder? J Am Geriatr Soc 1991;39:853-7. 2. Nicolle L. Urinary tract infection in long-term care facilities. Infect Control Hosp Epidemiol 1993;14:220-5. 3. Beier M. Management of urinary tract infections in the nursing home elderly: a proposed algorithmic approach. Int J Antimicrob Agents 1999;11:275-84. 4. Cohen H, Woloch B, Linder N, Vardi P, Barzilai A, Tel-Hoshomer I. Urine samples from disposal diapers: an accurate method for urine cultures. J Fam Pract 1997;44(3):290-2. 5. Beeram M, Dhanireddy R. Urinalysis: direct versus diaper collection. Clin Pediatr 1991;30(5):245-9. 6. Macfarlane P, Houghton C, Hughes C. Pad urine collection for early childhood urinary-tract infection. Lancet 1999;354:571. 7. Ahmad T, Vickers D, Campbell S, Coulthard M, Pedler S. Urine collection from disposable nappies. Lancet 1991;338:674-6. 8. Edwards A, van der Voort J, Newcombe R, Thayer H, Jones K. A urine analysis suitable for children’s nappies. J Clin Pathol 1997;50:569-71. 9. Belmin J, Hervias Y, Avello E, Oudart O, Durand I. Reliability of sampling urine from disposable diapers in elderly incontinent women. J Am Geriatr Soc 1993;42:1182-6.
July—August 2003
10. Garner J, Jarvis W, Emori T, Horanm T, Hughes J. CDC definitions for nosocomial infections 1988. Am J Infect Control 1988;16:128-40. 11. Chemstrip, Roche Diagnostics, Indianapolis, IN, 1999. 12. Brunzel N, editor. Fundamentals of urine and body fluid analysis. Philadelphia: W.B. Saunders; 1994. p.154. 13. Barker B, Ratcliff J, Turner G. Urine screening for leukocytes and bacteria by dipstick and reflectance spectrophotometry. Med Lab Sci 1989;46:97-100. 14. Pfaller M, Koontz F. Laboratory evaluation of leukocyte esterase and nitrite tests for the detection of bacteriuria. J Clin Microbiol 1985;21:840-2. 15. Weissfeld A, Sahm D, Forbes B. Selection of diagnostic tests. In: Weissfeld A, editor. Bailey and Scott’s diagnostic microbiology. 10th ed. St. Louis: Mosby; 1998. p.60-1. 16. Lachs M, Nachamkin I, Edelstein P, Goldman J, Feinstein A, Schwartz J. Spectrum bias in the evaluation of diagnostic tests: lessons from the rapid dipstick test for urinary tract infection. Ann Intern Med 1992;117:135-40. 17. Dawson-Saunders B, Trapp R, editors. Evaluating diagnostic procedures. In: Basic and clinical biostatistics. 2nd ed. Norwalk (CT): Appleton & Lange; 1994. p. 232-47. 18. Mims A, Norman D, Yamamura R, Yoshikawa T. Clinically inapparent (asymptomatic) bacteriuria in ambulatory elderly men: epidemiological, clinical and microbiological findings. J Am Geriatr Soc 1994;38:1209-14. 19. Nicolle L, Mayhew J, Bryan L. Outcomes following antimicrobial therapy for asymptomatic bacteriuria in elderly women residents in an institution. Age Ageing 1988:17:187-92. 20. Eberle C, Winsemius D, Garibaldi R. Risk factors and consequences of bacteriuria in non-catheterized nursing home residents. J Gerontol 1993;48(6):266-71. 21. Wingard E, Shales J, Mortimer E, Shales D. Colonization and cross-colonization of nursing home patients with trimethoprim-resistant gram-negative bacilli. Clin Infect Dis 1993;16:75-81.
SUSAN J. MIDTHUN, MS, RN, is a research nurse in the Clinical Laboratory Science Program at the University of North Dakota College of Nursing. RUTH A. PAUR, MS, MJ, ASCP, is the Interim Program Director of the Clinical Laboratory Sciences Program in the School of Medicine and Health Sciences at the University of North Dakota in Grand Forks. GLENDA LINDSETH, PhD, RN, RD, is professor and director of research in the University of North Dakota College of Nursing. SERGE P. VON DUVILLARD, PhD, FASCM, is professor and chair of the department of kinesiology and health promotion at the California State Polytechnic University in Pomona. Acknowledgment The authors wish to thank the Retirement Research Foundation in Chicago, who funded this study (grant #99-112). The authors also wish to thank Joleen Moser, Cheryl Cassibo, Dr. Bette Ide, Dr. Steven Schultz, Larry Lydick, Phyllis Nelson, and the nursing homes that allowed us to use their facilities. © 2003 by Mosby, Inc. All rights reserved. 0197-4572/2003 $30.00 + 0 doi:10.1067/mgn.2003.62
209
with
A
Urine
Dipstick Applied TO Incontinence Pads OF Nursing Home Residents Susan J. Midthun, MS, RN, Ruth A. Paur, MS, MJ, ASCP, Glenda Lindseth, PhD, RN, RD, and Serge P. Von Duvillard, PhD, FASCM
T
he purpose of this study was to evaluate a new method of initial on-site evaluation of bacteriuria in an incontinent nursing home population. Nitrite and a composite of nitrite and/or leukocyte esterase results of the new method were compared with clean-catch urine culture results of each participant to determine sensitivity, specificity, positive and negative predictive values, and efficiency. These findings were compared with results of the traditional dipstick urinalysis for bacteriuria assessment. The new method was as effective as the traditional method in assessing both the presence and absence of bacteriuria. Results of this study indicate the new dipstick/pad method may assist in the assessment of bacteriuria in incontinent nursing home residents. (Geriatr Nurs 2003;24:206-9)
Elders who are incontinent and confused pose a special challenge for determining the presence of a urinary tract infection (UTI). They may exhibit some UTI symptoms chronically and may not be able to communicate the presence of others, such as pain or temperature.1 Urine specimens may be difficult to obtain in this population, and catheterization itself may cause a UTI.2 A method to assess bacteriuria using pad urine would be easier and safer for these at-risk people. In the laboratory, a urine dipstick is immersed in a clean-catch urine specimen for initial evaluation of bacteriuria. The dipstick detects nitrite and leukocyte esterase. Nitrite is present when certain types of bacteria reduce dietary nitrate in the urine to nitrite. Leukocyte esterase is a component of white blood cells (WBCs), which often accompany bacteriuria.3 Assessment of bacteriuria and pyuria using urine from pads has reported varying results.4-9 A urine dipstick pressed into a wet incontinence pad of an elderly nursing home resident may be an effective method to assess bacteriuria. This method would be easy, 206
safe, and inexpensive in the initial evaluation of a UTI. It would allow simple laboratory data to be obtained without a laboratory facility, add objective data to the clinical picture, and assist in assessment and management of UTIs in the nursing home resident. The purpose of this study, therefore, was to evaluate a new method (dipstick/pad = dipstick pressed onto a recently wet incontinence pad) of initial on-site evaluation of bacteriuria in an incontinent nursing home population. METHOD A convenience sample of 98 residents was selected from lists generated by 6 nursing homes of incontinent residents who were antibiotic free for 14 days, had no recent record of vaginal discharge, and who could give clean-catch urine specimens. Informed consent was obtained from the residents or their responsible parties. Six to 10 participants per night were tested as follows. At the beginning of the night shift (22:00), 2 research assistants, each of whom had been given 1-hour instruction and practice in dipstick analysis, cleaned the urethral Geriatric Nursing
Volume 24
Number 4
area of the participant with soap and water. A urine incontinence pad (SCA Hygiene, Eddystone, Pa.) was applied. The pad was constructed of wood pulp and a superabsorbent polymer. Participants were monitored hourly, and wet pads were removed immediately and tested. Pads that were grossly contaminated with feces or contained less than 50 mL of urine by weight were not included in the study. A Chemstrip 10™ (Roche Diagnostics, Indianapolis, Ind.) dipstick was pressed onto the wettest part of the pad for 10 seconds. Timing of the nitrite and leukocyte esterase tests began immediately after dipstick removal and results read according to the color chart found on the dipstick bottle per the manufacturer’s guidelines. Leukocyte esterase results were recorded as negative, trace, 1+, or 2+. Nitrite results were positive or negative and recorded as such. Based on voiding habits, a clean-catch specimen was obtained in the early morning between 5 and 7:30 by the research assistants. The participant’s urethral area again was cleaned with soap and water. The resident voided into a new bedpan, urinal, or a hat placed in a toilet. The specimen then was poured into a sterile container. The clean-catch specimen was coded immediately and placed on ice in a cooler. Specimens were transported to the pathology department of the University of North Dakota School of Medicine and tested 3 to 8 hours after the participant voided. Urine analysis was performed in the following manner: a dipstick was immersed in the urine specimen and read per manufacturer’s instructions (dipstick/ua). Results were recorded in the same manner as the dipstick/pad method. Ten mL of the urine specimen then was centrifuged for 5 minutes at 400 x g. Nine mL of the supernatant was removed, and the sediment suspended in the remaining 1 mL sample. A drop of this suspension was placed on a slide and viewed under 450 X light microscopy. Results of 10 or less WBCs per high-powered field were considered negative, and more than 10 WBCs per high powered field positive for pyuria. Urine cultures were conducted on all samples. A 0.001mL calibrated bacteriological loop was used to inoculate the urine specimen onto MacConkey plates and tryptic soy agar plates that contained 5% sheep blood. Both plates were incubated at 37º C in ambient atmosphere for 48 hours. A culture result was considered positive if the urine grew one colony type (more than 100,000 colony-forming units per mL) within 48 hours. Background contaminating flora less than 25,000 colony-forming units per mL was not considered pathogenic. A single colony type of 50,000 colony-forming units per mL also was considered negative to adhere to the current recommendation of a positive urine culture.10 Nitrite and leukocyte esterase results may be affected by some antibiotics, nitrofurantoin, vitamin C (more than 500 mg/day), and phenazopyridine.11,12 These medications were not prescribed for participants in this study. Albumin more than 500 mg per mL is stated to affect July—August 2003
leukocyte esterase test results.11 No participant’s urine contained this amount of protein. No participant was acutely symptomatic for a UTI. The dipstick/pad and dipstick/ua methods were compared with culture results of the clean-catch urine specimen to determine sensitivity, specificity, positive and negative predictive values, and efficiency. Nitrite results were compared with culture results in bacteriuria detection. Because a composite of leukocyte esterase and nitrite has been shown to increase sensitivity of bacteriuria detection,13,14 2 composites of nitrite and/or leukocyte esterase results were compared with culture results for the detection of bacteriuria. The first consisted of a positive nitrite and/or 1+ or 2+ leukocyte esterase as indicative for bacteriuria. The second consisted of a positive nitrite and/or trace, 1+, or 2+ leukocyte esterase as indicative for bacteriuria. The following formulas for determining sensitivity, specificity, positive and negative predictive values, and efficiency of the dipstick/pad and dipstick/ua methods were used based on positive (pos) and negative (neg) results.15 Sensitivity = true pos/(true pos + false neg) X 100 Specificity = true neg/(true neg + false pos) X 100 Positive Predictive Value (PPV) = true pos/(true pos + false pos) X 100 Negative Predictive Value (NPV) = true neg/(true neg + false neg) X 100 Efficiency = true pos + true neg/(true pos + false pos + true neg + false neg) X 100
R E S U LT S In this study, 144 residents or their responsible parties gave consent for their participation. Forty-six were removed for reasons that included initiation of antibiotic therapy, death, or inability to give an incontinence pad containing 50 mL of urine or a 10 mL by clean-catch urine sample. A total of 98 residents were included in the study, the majority of whom were women (83.7%). Ages of the participants ranged from 64 to 101, with a mean age of 86. Urine specimens testing positive for bacteriuria were found in 27 or 27.6% of the sample. Of the study specimens positive for bacteriuria, 14 or 51.9% had accompanying pyuria of more than 10 WBCs per high powered field. The total number of pyuric specimens was 19 (19.4%), and 14 of these (73.7%) were bacteriuric. Nitrite results indicative for bacteriuria for both methods are shown in Table 1. These findings reflect other studies that reported pad urine as effective as clean-catch, suprapubic aspiration, or catheterized urine in bacteriuria detection.4,7,9 Table 2 identifies a composite of either positive nitrite and/or 1+ or 2+ leukocyte esterase as indicative for bacteriuria for both methods. Table 3 identifies a composite of either positive nitrite and/or any positive leukocyte esterase result (trace, 1+, or 2+) as indicative for bacteriuria for both methods. Sensitivity of both methods improved, whereas specificity decreased. 207
Table 1. Comparison of nitrite results as positive with culture results Dipstick/pad Positive
Negative
Dipstick/ua Total
Positive
Negative
Total
27 71 98
18 1 19
9 70 79
27 71 98
Culture Results Positive Negative Total
19 2 21
8 69 77
Dipstick/pad: Sensitivity 70.4%, Specificity 97.2%, PPV 90.5%, NPV 89.6%, Efficiency 89.8% Dipstick/ua: Sensitivity 66.7%, Specificity 98.6%, PPV 94.7%, NPV 88.6%, Efficiency 89.8%
Table 2. Comparison of nitrite and/or 1+ or 2+ leukocyte esterase results as positive with culture results Dipstick/pad Positive
Dipstick/ua
Negative
Total
Positive
Negative
Total
Culture Results Positive
21
6
27
22
5
27
Negative
17
54
71
10
61
71
Total
38
60
98
32
66
98
Dipstick/pad: Sensitivity 77.8%, Specificity 76.1%, PPV 56.2%, NPV 90.0%, Efficiency 76.5% Dipstick/ua: Sensitivity 81.5%, Specificity 85.9%, PPV 68.8%, NPV 92.4%, Efficiency 84.7%
DISCUSSION Negative results of the dipstick/pad method that included trace leukocyte esterase as positive (Table 3) were a good indication of no bacteriuria. However 73% of the positive results (30 of 71) were false. Positive results of the dipstick/pad method using nitrite alone were a very good indication of bacteriuric people. However 30% (n = 8) of bacteriuric specimens were missed in this application because of false negative results. PPV and NPV also were calculated for both methods. The PPV measures the probability that a positive result indicates the presence of the disease; the NPV measures the probability that a negative result indicates the absence of a disease.15 Predictive values, unlike sensitivity and specificity, take into consideration the prevalence of a disease in the population studied.15 Looking at these values, nitrite results alone of both methods had the best outcomes. Approximately 90% (19 of 21) positive results were true positive, and about 90% (69 of 77) results were true negative. Efficiency, the percentage of correct results per total sample population, also indicated nitrite results alone as the most accurate in identifying abacteriuria and bacteriuria. In both methods, 90% of people were correctly identified as positive or negative. The dipstick/pad method, done at the nursing home, was as effective as the commonly used laboratory test (dipstick/ua) in assessment of bacteriuria in the incontinent nursing home population.
208
L I M I TAT I O N S Results depend on the population studied.16,17 Dipstick/pad results for bacteriuria identification of symptomatic, incontinent people who are unable to give urine samples may not be identical to results of this study. Also, 92% of bacteria found in this study were nitrite producers. Although most bacteria found in other nursing home studies were nitrite producers, the rate varied.18-20 Results of the dipstick/pad method also may vary accordingly. C O N C L U S I O N S A N D R E C O M M E N D AT I O N S The nitrite results of the dipstick/pad method, done at the nursing home, were as effective as nitrite results of the dipstick/ua test, a commonly used laboratory method, in the assessment of both the presence and absence of bacteriuria. A quick, simple, noninvasive, and inexpensive method of initial assessment of bacteriuria used for incontinent nursing home residents would improve outcomes for this vulnerable population. For acutely symptomatic people identified as bacteriuric by positive nitrite results, intensified nursing interventions could be initiated, such as encouraging fluids and monitoring for increasing symptoms and possible further urinalysis. Results of these interventions could be monitored using the pad method as well. This test alone would not justify antibiotic treatment. Used in this context, a 10% error would seem acceptable. Using negative results,
Geriatric Nursing
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Number 4
Table 3. Comparison of nitrite and/or trace, 1+, or 2+ leukocyte esterase results as positive with culture results Dipstick/pad Positive
Negative
Dipstick/ua Total
Positive
Negative
Total
Culture Results Positive
26
1
27
26
1
27
Negative
30
41
71
16
55
71
Total
56
42
98
42
56
98
Dipstick/pad: Sensitivity 96.3%, Specificity 57.8%, PPV 46.4%, NPV 97.6%, Efficiency 68.4% Dipstick/ua: Sensitivity 96.3%, Specificity 77.5%, PPV 61.9%, NPV 98.2%, Efficiency 82.7%
a method that identified the absence of bacteriuria in acutely symptomatic people would decrease cost of unnecessary further testing and potential antibiotic treatment and focus scarce resources on more effective and less hazardous means of relief. Regarding the 1 in 10 false negative people, the clinical picture becomes especially important. Further studies may improve the dipstick/pad method by identifying those people who may be at risk for false negative results. These may include residents with nausea, vomiting, or diarrhea, possibly contributing to a lack of dietary nitrate, or urine “dribblers” who are unable to retain urine long enough for bacteria to convert nitrate to nitrite. Studies of a second dipstick/pad test the following night may show improvement in both PPV and NPV of this method. For asymptomatic people, bacteriuria screening is not recommended because it is not considered necessary to treat this condition. UTIs, however, are the major nosocomial nursing home infection, and nurses’ hands may be the primary mode of transmission.21 In the interest of infection control, nurses would seem justified in monitoring the presence or absence of all types of bacteriuria in the nursing home population. REFERENCES 1. Castle S, Norman D, Yeh M, Miller D, Yoshikawa T. Fever response in elderly nursing home residents: are the older truly colder? J Am Geriatr Soc 1991;39:853-7. 2. Nicolle L. Urinary tract infection in long-term care facilities. Infect Control Hosp Epidemiol 1993;14:220-5. 3. Beier M. Management of urinary tract infections in the nursing home elderly: a proposed algorithmic approach. Int J Antimicrob Agents 1999;11:275-84. 4. Cohen H, Woloch B, Linder N, Vardi P, Barzilai A, Tel-Hoshomer I. Urine samples from disposal diapers: an accurate method for urine cultures. J Fam Pract 1997;44(3):290-2. 5. Beeram M, Dhanireddy R. Urinalysis: direct versus diaper collection. Clin Pediatr 1991;30(5):245-9. 6. Macfarlane P, Houghton C, Hughes C. Pad urine collection for early childhood urinary-tract infection. Lancet 1999;354:571. 7. Ahmad T, Vickers D, Campbell S, Coulthard M, Pedler S. Urine collection from disposable nappies. Lancet 1991;338:674-6. 8. Edwards A, van der Voort J, Newcombe R, Thayer H, Jones K. A urine analysis suitable for children’s nappies. J Clin Pathol 1997;50:569-71. 9. Belmin J, Hervias Y, Avello E, Oudart O, Durand I. Reliability of sampling urine from disposable diapers in elderly incontinent women. J Am Geriatr Soc 1993;42:1182-6.
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10. Garner J, Jarvis W, Emori T, Horanm T, Hughes J. CDC definitions for nosocomial infections 1988. Am J Infect Control 1988;16:128-40. 11. Chemstrip, Roche Diagnostics, Indianapolis, IN, 1999. 12. Brunzel N, editor. Fundamentals of urine and body fluid analysis. Philadelphia: W.B. Saunders; 1994. p.154. 13. Barker B, Ratcliff J, Turner G. Urine screening for leukocytes and bacteria by dipstick and reflectance spectrophotometry. Med Lab Sci 1989;46:97-100. 14. Pfaller M, Koontz F. Laboratory evaluation of leukocyte esterase and nitrite tests for the detection of bacteriuria. J Clin Microbiol 1985;21:840-2. 15. Weissfeld A, Sahm D, Forbes B. Selection of diagnostic tests. In: Weissfeld A, editor. Bailey and Scott’s diagnostic microbiology. 10th ed. St. Louis: Mosby; 1998. p.60-1. 16. Lachs M, Nachamkin I, Edelstein P, Goldman J, Feinstein A, Schwartz J. Spectrum bias in the evaluation of diagnostic tests: lessons from the rapid dipstick test for urinary tract infection. Ann Intern Med 1992;117:135-40. 17. Dawson-Saunders B, Trapp R, editors. Evaluating diagnostic procedures. In: Basic and clinical biostatistics. 2nd ed. Norwalk (CT): Appleton & Lange; 1994. p. 232-47. 18. Mims A, Norman D, Yamamura R, Yoshikawa T. Clinically inapparent (asymptomatic) bacteriuria in ambulatory elderly men: epidemiological, clinical and microbiological findings. J Am Geriatr Soc 1994;38:1209-14. 19. Nicolle L, Mayhew J, Bryan L. Outcomes following antimicrobial therapy for asymptomatic bacteriuria in elderly women residents in an institution. Age Ageing 1988:17:187-92. 20. Eberle C, Winsemius D, Garibaldi R. Risk factors and consequences of bacteriuria in non-catheterized nursing home residents. J Gerontol 1993;48(6):266-71. 21. Wingard E, Shales J, Mortimer E, Shales D. Colonization and cross-colonization of nursing home patients with trimethoprim-resistant gram-negative bacilli. Clin Infect Dis 1993;16:75-81.
SUSAN J. MIDTHUN, MS, RN, is a research nurse in the Clinical Laboratory Science Program at the University of North Dakota College of Nursing. RUTH A. PAUR, MS, MJ, ASCP, is the Interim Program Director of the Clinical Laboratory Sciences Program in the School of Medicine and Health Sciences at the University of North Dakota in Grand Forks. GLENDA LINDSETH, PhD, RN, RD, is professor and director of research in the University of North Dakota College of Nursing. SERGE P. VON DUVILLARD, PhD, FASCM, is professor and chair of the department of kinesiology and health promotion at the California State Polytechnic University in Pomona. Acknowledgment The authors wish to thank the Retirement Research Foundation in Chicago, who funded this study (grant #99-112). The authors also wish to thank Joleen Moser, Cheryl Cassibo, Dr. Bette Ide, Dr. Steven Schultz, Larry Lydick, Phyllis Nelson, and the nursing homes that allowed us to use their facilities. © 2003 by Mosby, Inc. All rights reserved. 0197-4572/2003 $30.00 + 0 doi:10.1067/mgn.2003.62
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