- Email: [email protected]
Evaluation of the Beckman ASTRA enzyme system
Evaluation of the Beckman ASTRA Enzyme System J O S E P H E. D E V I N E , R O Y L A L E X A N D E R , JR., J U D I T H A. B E H R L E , D E B R A A. S L E M M E N S , L U C Y H. D R U R Y , and R O N A L D E. S Z M U R L O D e p a r t m e n t of Pathology, St. Louis University School of M e d i c i n e and Clinical Laboratories, St. Louis University Hospital, St. Louis, M O 6 3 1 0 4 We have evaluated the ASTRA enzyme analyzer. Six enzymes can be analyzed individually or as part of a larger profile of chemistry tests. The system can analyze all six enzymes at a rate of 35-40 specimens per hour. Within-run and day-to-day precision were comparable to that of other enzyme analyzers. A useful feature of the ASTRA enzyme analyzer permits the automatic reassay of specimens havingactivities that exceed certaindefined limits. A comparison of methodsfor the ASTRA enzymeanalyzerwith those used on the SMA 12/60 and the ABA-100 showed good correlation with minimal random error.
KEY WORDS: automated enzyme analysis, automatic data processing computer. he ASTRA enzyme system (Beckman Instruments, Fullerton, CA 94623), a modification of the ASTRA T 8, has been in operation in this laboratory for two years. Since an evaluation of the ASTRA enzyme system has already appeared in the literature (1), this study will emphasize data which have not been previously reported. Comparative analyses for AST, LD, and ALP have been performed on the SMA 12/60 (Technicon Instruments, Tarrytown, NY 10591) and for ALT, CK, and GGT on the ABA-100 (Abbott Laboratories, Irving TX 75061). A reference range study has been carried out on specimens obtained from routine blood donations to the American Red Cross. Materials and m e t h o d s Reagents and consumables for the ASTRA enzyme system were supplied by Beckman. For this study, enzyme activities were determined at 37°C. Assays can also be carried out at 30°C. CK activity is determined by a modification of the methodologies of Szasz et al. (2) and Morin (3). The reagents include the CK activator, monothioglycerol. LD activity is determined by a modification of the method of Wacker et al. (4) in which lactate is converted to pyruvate. AST and ALT are both determined by modifications of the method of Henry et al. (5). ALP activity is determined by a modification of the method of Bowers and McComb (6). In this modification a carCorrespondence: Joseph E. Devine, Ph.D., St. Louis University Hospital, 1325 South Grand Boulevard, St. Louis MO 631O4. USA. This paper is based on a presentation by the authors at the 36th national meeting of the American Association for Clinical Chemistry, July 29-August 3, 1984, Washington, D.C. Manuscript received February 11, 1985; revised July 24, 1985; accepted August 20, 1985. 16
bonate buffer is used in place of an amine buffer. GGT activity is determined by a modification of the method of Szasz (7, 8). ORDAC (overrange detection and correction) is a feature of the enzyme system that provides automatic reanalysis of specimens that have high activity. If the absorbance change per rain exceeds defined limits, ORDAC is activated and a smaller sample (5 ~L) of serum is analyzed. The total activity is then calculated based on the smaller sample volume. Instruments used in the comparison study were the SMA 12/60 and the ABA-100. The SMA 12/60 methods were all unmodified Technicon procedures. The ABA100 was used for the determination of CK, ALT and GGT. CK activity was determined using Roche Isomune-CK substrate (Roche Diagnostics, Nutley, NJ 07110). This is the procedure of Rosalki (9) run at 37°C with no thiol activator. ALT activity was determined at 30°C using Calbiochem GPT Stat-Pak reagents (Behring Diagnostics, La Jolla, CA 92037). GGT activity was determined at 30°C using Worthington Statzyme reagents (Cooper Biomedical, Inc., Malvern, PA 19355). SPECIMENS Patient sera and serum pools were used in most of the studies. All specimens were submitted to the clinical laboratories for routine enzyme testing and were drawn either in Corvac or red top blood collection tubes (Monoject Scientific, St. Louis, MO 63146). Specimens were analyzed by all methods within 8 h following blood collection. Serum tubes were covered with laboratory film between analyses. Specimens for the reference range study were obtained from blood donations collected by the Missouri/ Illinois Regional Blood Services of the American Red Cross, St. Louis, MO. These specimens were drawn in red top tubes and maintained on ice until centrifuged. All analyses were performed on the day the specimens were obtained. The following control sera were used in the study: Beckman Triad levels 1, 2 and 3, and Beckman Enzyme Verifier. CALIBRATION The SMA 12/60 was calibrated with Sera Chem Reference Serum (lot # 524-032, Fisher Diagnostics, Orangeburg, NY 10962) using values assigned by the manufacturer. Calibration of the ABA-100 was based on factors derived from the protocol for each assay. CLINICAL BIOCHEMISTRY,VOLUME 19, FEBRUARY 1986
BECKMAN ASTRA ENZYME SYSTEM 310q
AI"
,,o ALT
~ g=(0.Ta)×+&l 2484 Sy/x=4.38 I r =0.993
120
,// ,~
...y
I ~
=i
9o./. 60-
2
-
62
/
y=(1.18)x+ 10.7 Sy/x=2.79 r=0.992 / N=226
~ 30
0
6'2
124
186
248
310
30
U/L, SMA 12160 620-
60
120
90
150
IUIL, ABA 100
LD
GGW
400-
y=(0.81)x-9.0 496
y=(1.22)x+0.6 Sy/x=2.58 r =__0,999
320
/
Figure 1 - - Regression analysis and correlation of methods for assaying enzymes using the ASTRA enzyme system, the SMA 12/60, and the ABA-100.
~ 240" .¢
~248-
'~160
124~
80
124
248
372
496
620
8'o
40
30!
ALP
1150-.
q y=(O,85x+2.1 920-
,,
i r=0.981
i
~/" •
,=276
~
"
o90:
.." . . .
~.~144~
~ ".~
5
"
°!i O
72
144
216
' 2~,o
' 3~o
' 4bo
IUIL, ABA 100
U/L, SMA 12160
288
360
y = (1.45)x- 21.0 Sy / X= 20.37 r=0.997 N=205
/
460
0
/
CK
i
,
230
i
i
460
r
i
690
I
9~o
~1~o
lUlL, ABA 100
U/L, SMA 12160
Within-run precision was determined with several serum pools that provided low normal, high normal, and above normal activities. The CV for low normal
pools ranged from 2.2-8.2% and from 1.0-2.4% for high normal and abnormal pools (Table 1). Day-to-day precision was measured for 25 days by assaying one control with normal and three controls with abnormal activities. The CV for the normal control was 3.2-5.4%, and 1.6-5.5% for the abnormal controls (Table 2). Carryover was evaluated by assaying three specimens of a normal control that were immediately preceded by a single control having an activity up to 20 times that of the normal control (10). The average carryover in IU/L followed by the percentage of interaction was AST, 1.0 (0.3%); ALT, 0.3 (0.1%); LD, 2.0 (0.3%); GGT, 1.0 (0.3%); CK, 1.3 (0.1%); and ALP, 0.3 (0.1%). The manufacturer does not supply any data on carryover. The manufacturer specifies that the acceptable range of temperature control for the cuvettes is 37 -+ 0.5°C. Daily measurements of this temperature using a thermistor cuvette probe supplied with the instrument have shown a variation of -+0.1°C. Measurement of cuvette temperatures with a thermistor standardized against an NBS reference thermometer showed a
CLINICAL BIOCHEMISTRY, VOLUME 19, FEBRUARY 1986
17
TABLE 1 Within-run Precision of the ASTRA Enzyme System for Normal and Abnormal Serum Enzyme Activities (IU/L) n = 20
AST
ALT
Mean SD CV,%
18.6 1.3 7.0
14.4 0.9 6.2
74.3 1.6 2.2
14.4 1.2 8.2
42.4 1.9 4.6
39.9 1.0 2.6
Mean
41.8 1.0 2.4
57.7 1.1 1.9
149.2 2.5 1.7
55.5 1.0 1.8
161.0 3.2 2.0
116.0 1.4 1.2
143.4 1.8 1.3
201.8 2.0 1.0
452.6 6.0 1.3
308.0 3.5 1.1
1145.9 12.4 1.1
340.2 4.2 1.2
CV,% Mean CV,%
LD
GGT
CK
ALP
Manufacturer's CV, normal and abnormal range: 3.5-10%.
Results
DEVINE, ALEXANDER, BEHRLE, SLEMMENS, DRURY AND SZMURLO TABLE 2
The ASTRA enzyme system has been in continuous operation in this laboratory. Approximately 90 speci-
mens are assayed every work day. The majority of these assays are part of a nine-test profile that includes analyses for total protein, albumin, calcium, and total bilirubin. Studies of within-run and day-to-day precision are comparable to those reported for other automated systems (12-16). The within-run precision t h a t we obtained (Table 1) is better than that which the manufacturer specifies for the normal and abnormal range. Our studies indicate that the within-run precision improves markedly when enzyme values increase from the low to the high normal and abnormal ranges. The m a n u f a c t u r e r does not have day-to-day precision data available for comparison. Occasionally, specimens assayed for ALT or AST have activities approaching 1 IU/L. When these specimens have transaminase activity less t h a n about 9 IU/L, the change in absorbance approaches that of the reagent blank and the results will be suppressed and recorded as out of range. We encounter about one of these specimens every day. An approximate activity can be measured in these specimens by diluting them one plus one with an assayed control and correcting the result for the activity of the control. Out-of-range values (low activities) have only occurred with AST and ALT but more frequently with the latter. ORDAC is a feature of the ASTRA enzyme system t h a t automatically reassays specimens having activities t h a t exceed certain defined limits. The within-run precision for ORDAC was found to be better t h a n that reported by the manufacturer (CV = 10%). The activities obtained with ORDAC agreed well with values obtained from assays of dilutions of the specimens. ORDAC results in savings of time and eliminates random error t h a t occurs if dilutions of serum are prepared for reassay. If specimens with known high activity are to be analyzed, they can be programmed for ORDAC prior to the run. Regression analysis of results obtained with the ASTRA, the SMA 12/60, and the ABA-100 showed good correlation with minimal random error (Figure 1). The start-up time for the ASTRA enzyme system i~ about 20 min. This includes replacement of reagent packs, calibration, and cuvette absorbance and reagent blank checks. During an 8 h shift, the loading of new reagent packs usually requires an additional 30 min. It a reagent pack has a volume of reagent left t h a t i~ equivalent to less t h a n 10 tests, it is replaced with new pack. No difficulties have been encountered wit~ the stability of reagents during the three-day limit specified by the manufacturer. In our laboratory, the a m o u n t of reagent discarded in an 8 h shift is equiv. alent to about 15 single tests. If no down time is experienced, the ASTRA enzyme system can assay 35-40 specimens per hour. Overall maintenance requires about 4 h per week. Down time has averaged about 1 h per week and is caused by failures of tubing, printhead, light sources, and detectors. Discs for the microprocessor are replaced once a month. This virtually eliminates down time due to disc failure. Down time of about 10 min per month occurs due to the formation of bubbles in the cuvettes This is corrected by flushing the cuvettes with rinse
18
CLINICAL BIOCHEMISTRY, VOLUME 19, FEBRUARY 1986
Day-to-Day Precision of the ASTRA Enzyme System Using Normal and Abnormal Beckman Controls (IU/L) n = 25
AST
ALT
LD
GGT
CK
ALP
31.2 1.4 4.5
28.9 1.4 4.8
121.2 4.8 4.0
24.6 1.0 4.1
111.3 6.0 5.4
49.5 1.6 3.2
76.5 1.8 2.4
70.3 3.9 5.5
343.6 18.8 5.5
72.0 1.6 2.2
228.2 8.0 3.5
120.3 2.4 2.2
187.0 3.0 1.6
163.2 7.4 4.5
216.1 6.5 3.0
153.5 2.6 1.7
483.2 13.1 2.7
179.5 4.0 2.2
Enzyme Verifier Mean 350.3 SD 11.0 CV, % 3.1
344.2 6.2 1.8
596.7 15.0 2.5
703.0 15.4 2.2
981.6 26.8 2.7
331.9 5.8 1.7
Triad 1 Mean SD CV, % Triad 2 Mean SD CV, % Triad 3 Mean SD CV, %
Manufacturer's CV: Not given. temperature of 37.2°C for one module and 37.4°C for the other. Regression analysis showed good correlation of the ASTRA methods with the comparison methods and minimal random error (Figure 1). The regression analysis is t h a t of Deming (11) and assumes imprecision in all methods of analysis. Activities were not corrected for differences in the temperature at which enzymes were assayed. ORDAC is activated by the microprocessor if activities of specific enzymes exceed the following limits: AST, ALT, and ALP, 400 IU/L; LD, 700 IU/L; GGT, 750 IU/L; and CK, 1200 IU/L. The within-run precision of ORDAC was calculated from 10 repetitive assays of 6 sera with high activity. The mean activities (IU/L) obtained were AST, 1589; ALT, 1050; LD, 1141; GGT, 1138, CK, 1557; and ALP, 760. The CV's were AST, 2.4%; ALT, 7.7%; LD, 1.5%; GGT, 1.7%; CK, 1.3%; and ALP, 5.4%. ORDAC values were also compared with the average calculated total activities obtained from the assay of three dilutions of each specimen without activation of ORDAC. The percent differences between ORDAC and the calculated total activities were as follows: AST, -5.3%; ALT, +7.3%; LD, +2.4%; GGT, +4.5%; CK, +0.3%; and ALP, +4.9%. Reference limits were calculated from assays of blood obtained from routine donations to the American Red Cross by 375 individuals (143 male, 232 female) ages 1 9 - 6 5 . The distribution of values for all enzymes was non-gaussian. Reference limits (95%) were as follows: AST, 1 4 - 4 3 ; ALT 1 2 - 5 8 ; LD, 8 3 - 1 7 1 ; GGT, 8 - 5 7 ; CK, 3 6 - 2 5 3 ; and ALP, 3 2 - 1 0 4 IU/L. Discussion
BECKMAN ASTRA ENZYME SYSTEM solution. Dispenser assemblies have to be replaced every four m o n t h s and, occasionally, at more frequent intervals. The ASTRA enzyme s y s t e m h a s performed well in this l a b o r a t o r y and technical support from the m a n u facturer has been good. Acknowledgement The authors would like to thank Drs. Norman B. Fizette and Marilyn F. M. Johnston who made arrangements to secure blood from the Missouri/Illinois Regional Blood Services of the American Red Cross, for the normal value study.
References 1. Janssen JW, Verdegaal JM, Visser RWJ. Performance of the ASTRA enzyme systems evaluated. Clin Chem 1984; 30: 1830-3. 2. Szasz G, Gruber W, Brent W. Creatine kinase in serum: 1. Determination of optimum reaction conditions. Clin Chem 1976; 22: 650-6. 3. Morin LG. Creatine kinase: Re-examination of optimum reaction conditions. Clin Chem 1977; 23: 1569-75. 4. Wacker WEC, Ulmer DD, Vallee BL. Metalloenzymes and myocardial infarction II. Malic and lactic dehydrogenase activities and zinc concentrations in serum. N Engl J Med 1956; 255: 449-56. 5. Henry RJ, Chiamori N, Golub OJ, Berkman S. Revised spectro-photometric methods for the determination of glutamic-oxalacetic transaminase, glutamic-pyruvic transaminase, and lactic acid dehydrogenase. A m J Clin Path
CLINICALBIOCHEMISTRY, VOLUME 19, FEBRUARY 1986
1960; 34: 381-98. 6. Bowers GN, McComb RB. A continuous spectrophotometric method for measuring the activity of serum alkaline phosphatase. Clin Chem 1966; 12: 70-89. 7. Szasz G. A kinetic photometric method for serum gammaglutamyl transpeptidase. Clin Chem 1969; 15: 124-36. 8. Szasz G. New substrates for measuring gamma-glutamyl transpeptidase activity. Z Klin Chem Klin Biochem 1974; 12: 228. 9. Rosalki SB. An improved procedure for serum creatine phosphokinase determination. J Lab Clin Med 1969; 15: 124-36. 10. Broughton PMG, Gowenlock AH, McCormack JJ, Neill DW. A revised scheme for the evaluation of automatic instruments for use in clinical chemistry. A n n Clin Biochem 1974; 11: 207-18. 11. Deming WE. Statistical Adjustment of Data. P. 184. New York, NY: John Wiley and Sons, 1943. 12. Kineiko RW, Floering DA, Morrissey M. Laboratory evaluation of the Boehringer Mannheim ~Hitachi 705" automatic analyzer. Clin Chem 1983; 29: 688-91. 13. Passey R, Gillum RL, Giles ML, Fuller JB. Evaluation of the Beckman ~'System TR Enzyme Analyzer". Clin Chem 1975; 21: 1107-12. 14. Schwartz MK, Statland BE, Coughlin J, et al. Chemical and clinical evaluation of the Random Access Analyzer ~RA-1000". CIin Chem 1984; 30: 364-8. 15. Douville P, Forest J-C. Performance of the Hitachi 705 evaluated. Clin Chem 1983; 29: 692-6. 16. Robinson CA, Proelss H, Stabler TV. Laboratory evaluation of the Boehring Mannheim '~Diagnostic M" automated discrete analyzer. Clin Chem 1982; 28: 105-9.
19
KEY WORDS: automated enzyme analysis, automatic data processing computer. he ASTRA enzyme system (Beckman Instruments, Fullerton, CA 94623), a modification of the ASTRA T 8, has been in operation in this laboratory for two years. Since an evaluation of the ASTRA enzyme system has already appeared in the literature (1), this study will emphasize data which have not been previously reported. Comparative analyses for AST, LD, and ALP have been performed on the SMA 12/60 (Technicon Instruments, Tarrytown, NY 10591) and for ALT, CK, and GGT on the ABA-100 (Abbott Laboratories, Irving TX 75061). A reference range study has been carried out on specimens obtained from routine blood donations to the American Red Cross. Materials and m e t h o d s Reagents and consumables for the ASTRA enzyme system were supplied by Beckman. For this study, enzyme activities were determined at 37°C. Assays can also be carried out at 30°C. CK activity is determined by a modification of the methodologies of Szasz et al. (2) and Morin (3). The reagents include the CK activator, monothioglycerol. LD activity is determined by a modification of the method of Wacker et al. (4) in which lactate is converted to pyruvate. AST and ALT are both determined by modifications of the method of Henry et al. (5). ALP activity is determined by a modification of the method of Bowers and McComb (6). In this modification a carCorrespondence: Joseph E. Devine, Ph.D., St. Louis University Hospital, 1325 South Grand Boulevard, St. Louis MO 631O4. USA. This paper is based on a presentation by the authors at the 36th national meeting of the American Association for Clinical Chemistry, July 29-August 3, 1984, Washington, D.C. Manuscript received February 11, 1985; revised July 24, 1985; accepted August 20, 1985. 16
bonate buffer is used in place of an amine buffer. GGT activity is determined by a modification of the method of Szasz (7, 8). ORDAC (overrange detection and correction) is a feature of the enzyme system that provides automatic reanalysis of specimens that have high activity. If the absorbance change per rain exceeds defined limits, ORDAC is activated and a smaller sample (5 ~L) of serum is analyzed. The total activity is then calculated based on the smaller sample volume. Instruments used in the comparison study were the SMA 12/60 and the ABA-100. The SMA 12/60 methods were all unmodified Technicon procedures. The ABA100 was used for the determination of CK, ALT and GGT. CK activity was determined using Roche Isomune-CK substrate (Roche Diagnostics, Nutley, NJ 07110). This is the procedure of Rosalki (9) run at 37°C with no thiol activator. ALT activity was determined at 30°C using Calbiochem GPT Stat-Pak reagents (Behring Diagnostics, La Jolla, CA 92037). GGT activity was determined at 30°C using Worthington Statzyme reagents (Cooper Biomedical, Inc., Malvern, PA 19355). SPECIMENS Patient sera and serum pools were used in most of the studies. All specimens were submitted to the clinical laboratories for routine enzyme testing and were drawn either in Corvac or red top blood collection tubes (Monoject Scientific, St. Louis, MO 63146). Specimens were analyzed by all methods within 8 h following blood collection. Serum tubes were covered with laboratory film between analyses. Specimens for the reference range study were obtained from blood donations collected by the Missouri/ Illinois Regional Blood Services of the American Red Cross, St. Louis, MO. These specimens were drawn in red top tubes and maintained on ice until centrifuged. All analyses were performed on the day the specimens were obtained. The following control sera were used in the study: Beckman Triad levels 1, 2 and 3, and Beckman Enzyme Verifier. CALIBRATION The SMA 12/60 was calibrated with Sera Chem Reference Serum (lot # 524-032, Fisher Diagnostics, Orangeburg, NY 10962) using values assigned by the manufacturer. Calibration of the ABA-100 was based on factors derived from the protocol for each assay. CLINICAL BIOCHEMISTRY,VOLUME 19, FEBRUARY 1986
BECKMAN ASTRA ENZYME SYSTEM 310q
AI"
,,o ALT
~ g=(0.Ta)×+&l 2484 Sy/x=4.38 I r =0.993
120
,// ,~
...y
I ~
=i
9o./. 60-
2
-
62
/
y=(1.18)x+ 10.7 Sy/x=2.79 r=0.992 / N=226
~ 30
0
6'2
124
186
248
310
30
U/L, SMA 12160 620-
60
120
90
150
IUIL, ABA 100
LD
GGW
400-
y=(0.81)x-9.0 496
y=(1.22)x+0.6 Sy/x=2.58 r =__0,999
320
/
Figure 1 - - Regression analysis and correlation of methods for assaying enzymes using the ASTRA enzyme system, the SMA 12/60, and the ABA-100.
~ 240" .¢
~248-
'~160
124~
80
124
248
372
496
620
8'o
40
30!
ALP
1150-.
q y=(O,85x+2.1 920-
,,
i r=0.981
i
~/" •
,=276
~
"
o90:
.." . . .
~.~144~
~ ".~
5
"
°!i O
72
144
216
' 2~,o
' 3~o
' 4bo
IUIL, ABA 100
U/L, SMA 12160
288
360
y = (1.45)x- 21.0 Sy / X= 20.37 r=0.997 N=205
/
460
0
/
CK
i
,
230
i
i
460
r
i
690
I
9~o
~1~o
lUlL, ABA 100
U/L, SMA 12160
Within-run precision was determined with several serum pools that provided low normal, high normal, and above normal activities. The CV for low normal
pools ranged from 2.2-8.2% and from 1.0-2.4% for high normal and abnormal pools (Table 1). Day-to-day precision was measured for 25 days by assaying one control with normal and three controls with abnormal activities. The CV for the normal control was 3.2-5.4%, and 1.6-5.5% for the abnormal controls (Table 2). Carryover was evaluated by assaying three specimens of a normal control that were immediately preceded by a single control having an activity up to 20 times that of the normal control (10). The average carryover in IU/L followed by the percentage of interaction was AST, 1.0 (0.3%); ALT, 0.3 (0.1%); LD, 2.0 (0.3%); GGT, 1.0 (0.3%); CK, 1.3 (0.1%); and ALP, 0.3 (0.1%). The manufacturer does not supply any data on carryover. The manufacturer specifies that the acceptable range of temperature control for the cuvettes is 37 -+ 0.5°C. Daily measurements of this temperature using a thermistor cuvette probe supplied with the instrument have shown a variation of -+0.1°C. Measurement of cuvette temperatures with a thermistor standardized against an NBS reference thermometer showed a
CLINICAL BIOCHEMISTRY, VOLUME 19, FEBRUARY 1986
17
TABLE 1 Within-run Precision of the ASTRA Enzyme System for Normal and Abnormal Serum Enzyme Activities (IU/L) n = 20
AST
ALT
Mean SD CV,%
18.6 1.3 7.0
14.4 0.9 6.2
74.3 1.6 2.2
14.4 1.2 8.2
42.4 1.9 4.6
39.9 1.0 2.6
Mean
41.8 1.0 2.4
57.7 1.1 1.9
149.2 2.5 1.7
55.5 1.0 1.8
161.0 3.2 2.0
116.0 1.4 1.2
143.4 1.8 1.3
201.8 2.0 1.0
452.6 6.0 1.3
308.0 3.5 1.1
1145.9 12.4 1.1
340.2 4.2 1.2
CV,% Mean CV,%
LD
GGT
CK
ALP
Manufacturer's CV, normal and abnormal range: 3.5-10%.
Results
DEVINE, ALEXANDER, BEHRLE, SLEMMENS, DRURY AND SZMURLO TABLE 2
The ASTRA enzyme system has been in continuous operation in this laboratory. Approximately 90 speci-
mens are assayed every work day. The majority of these assays are part of a nine-test profile that includes analyses for total protein, albumin, calcium, and total bilirubin. Studies of within-run and day-to-day precision are comparable to those reported for other automated systems (12-16). The within-run precision t h a t we obtained (Table 1) is better than that which the manufacturer specifies for the normal and abnormal range. Our studies indicate that the within-run precision improves markedly when enzyme values increase from the low to the high normal and abnormal ranges. The m a n u f a c t u r e r does not have day-to-day precision data available for comparison. Occasionally, specimens assayed for ALT or AST have activities approaching 1 IU/L. When these specimens have transaminase activity less t h a n about 9 IU/L, the change in absorbance approaches that of the reagent blank and the results will be suppressed and recorded as out of range. We encounter about one of these specimens every day. An approximate activity can be measured in these specimens by diluting them one plus one with an assayed control and correcting the result for the activity of the control. Out-of-range values (low activities) have only occurred with AST and ALT but more frequently with the latter. ORDAC is a feature of the ASTRA enzyme system t h a t automatically reassays specimens having activities t h a t exceed certain defined limits. The within-run precision for ORDAC was found to be better t h a n that reported by the manufacturer (CV = 10%). The activities obtained with ORDAC agreed well with values obtained from assays of dilutions of the specimens. ORDAC results in savings of time and eliminates random error t h a t occurs if dilutions of serum are prepared for reassay. If specimens with known high activity are to be analyzed, they can be programmed for ORDAC prior to the run. Regression analysis of results obtained with the ASTRA, the SMA 12/60, and the ABA-100 showed good correlation with minimal random error (Figure 1). The start-up time for the ASTRA enzyme system i~ about 20 min. This includes replacement of reagent packs, calibration, and cuvette absorbance and reagent blank checks. During an 8 h shift, the loading of new reagent packs usually requires an additional 30 min. It a reagent pack has a volume of reagent left t h a t i~ equivalent to less t h a n 10 tests, it is replaced with new pack. No difficulties have been encountered wit~ the stability of reagents during the three-day limit specified by the manufacturer. In our laboratory, the a m o u n t of reagent discarded in an 8 h shift is equiv. alent to about 15 single tests. If no down time is experienced, the ASTRA enzyme system can assay 35-40 specimens per hour. Overall maintenance requires about 4 h per week. Down time has averaged about 1 h per week and is caused by failures of tubing, printhead, light sources, and detectors. Discs for the microprocessor are replaced once a month. This virtually eliminates down time due to disc failure. Down time of about 10 min per month occurs due to the formation of bubbles in the cuvettes This is corrected by flushing the cuvettes with rinse
18
CLINICAL BIOCHEMISTRY, VOLUME 19, FEBRUARY 1986
Day-to-Day Precision of the ASTRA Enzyme System Using Normal and Abnormal Beckman Controls (IU/L) n = 25
AST
ALT
LD
GGT
CK
ALP
31.2 1.4 4.5
28.9 1.4 4.8
121.2 4.8 4.0
24.6 1.0 4.1
111.3 6.0 5.4
49.5 1.6 3.2
76.5 1.8 2.4
70.3 3.9 5.5
343.6 18.8 5.5
72.0 1.6 2.2
228.2 8.0 3.5
120.3 2.4 2.2
187.0 3.0 1.6
163.2 7.4 4.5
216.1 6.5 3.0
153.5 2.6 1.7
483.2 13.1 2.7
179.5 4.0 2.2
Enzyme Verifier Mean 350.3 SD 11.0 CV, % 3.1
344.2 6.2 1.8
596.7 15.0 2.5
703.0 15.4 2.2
981.6 26.8 2.7
331.9 5.8 1.7
Triad 1 Mean SD CV, % Triad 2 Mean SD CV, % Triad 3 Mean SD CV, %
Manufacturer's CV: Not given. temperature of 37.2°C for one module and 37.4°C for the other. Regression analysis showed good correlation of the ASTRA methods with the comparison methods and minimal random error (Figure 1). The regression analysis is t h a t of Deming (11) and assumes imprecision in all methods of analysis. Activities were not corrected for differences in the temperature at which enzymes were assayed. ORDAC is activated by the microprocessor if activities of specific enzymes exceed the following limits: AST, ALT, and ALP, 400 IU/L; LD, 700 IU/L; GGT, 750 IU/L; and CK, 1200 IU/L. The within-run precision of ORDAC was calculated from 10 repetitive assays of 6 sera with high activity. The mean activities (IU/L) obtained were AST, 1589; ALT, 1050; LD, 1141; GGT, 1138, CK, 1557; and ALP, 760. The CV's were AST, 2.4%; ALT, 7.7%; LD, 1.5%; GGT, 1.7%; CK, 1.3%; and ALP, 5.4%. ORDAC values were also compared with the average calculated total activities obtained from the assay of three dilutions of each specimen without activation of ORDAC. The percent differences between ORDAC and the calculated total activities were as follows: AST, -5.3%; ALT, +7.3%; LD, +2.4%; GGT, +4.5%; CK, +0.3%; and ALP, +4.9%. Reference limits were calculated from assays of blood obtained from routine donations to the American Red Cross by 375 individuals (143 male, 232 female) ages 1 9 - 6 5 . The distribution of values for all enzymes was non-gaussian. Reference limits (95%) were as follows: AST, 1 4 - 4 3 ; ALT 1 2 - 5 8 ; LD, 8 3 - 1 7 1 ; GGT, 8 - 5 7 ; CK, 3 6 - 2 5 3 ; and ALP, 3 2 - 1 0 4 IU/L. Discussion
BECKMAN ASTRA ENZYME SYSTEM solution. Dispenser assemblies have to be replaced every four m o n t h s and, occasionally, at more frequent intervals. The ASTRA enzyme s y s t e m h a s performed well in this l a b o r a t o r y and technical support from the m a n u facturer has been good. Acknowledgement The authors would like to thank Drs. Norman B. Fizette and Marilyn F. M. Johnston who made arrangements to secure blood from the Missouri/Illinois Regional Blood Services of the American Red Cross, for the normal value study.
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