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International classification of diseases and current procedural terminology codes underestimated thrombolytic use for ischemic stroke
Journal of Clinical Epidemiology 59 (2006) 856–858
International classification of diseases and current procedural terminology codes underestimated thrombolytic use for ischemic stroke Adnan I. Qureshi*, Pansy Harris-Lane, Faisal Siddiqi, Jawad F. Kirmani Epidemiological and Outcomes Research Division, Zeenat Qureshi Stroke Research Center, Department of Neurology and Neurosciences, University of Medicine and Dentistry of New Jersey, 90 Bergen Streeet, DOC-8100, Newark, NJ 07103, USA Accepted 7 January 2006
Abstract Background and Objective: To determine the accuracy of recently introduced International Classification of Diseases Ninth Revision (ICD-9) procedure and Current Procedural Terminology (CPT) codes designed for injection or infusion of thrombolytic agents. Materials and Methods: We determined the accuracy of ICD-9 procedure code 99.10 and CPT codes 37201, 37202 for use of thrombolysis in ischemic stroke by comparing procedure codes of University Hospital discharge data with a concurrent prospective registry. Results: Of the 369 ischemic stroke patients, 49 (13.3%) received either intravenous and/or intraarterial thrombolysis. The sensitivity and specificity for ICD-9 procedure code 99.10 was 55% and 98% and CPT procedure code 37201 and 37202 was 49% and 99%. Identification by either ICD-9 codes or CPT codes yielded a high sensitivity and specificity of 82% and 98%. Conclusions: The use of ICD-9 and CPT codes alone may underestimate the use of thrombolytics using national and regional database. Best results are achieved when a combination of ICD-9 and CPT codes are used to identify the use of thrombolytics. Ó 2006 Elsevier Inc. All rights reserved. Keywords: Current Procedural Terminology (CPT); International Classification of Diseases Ninth Revision (ICD-9); Ischemic Stroke; Stroke; Thrombolysis; Thrombolytics
1. Introduction Hospital discharge diagnoses are routinely coded using International Classification of Diseases, 9th Revision (ICD-9) [1]. Previous studies have validated ICD-9 diagnoses codes for identification of incident cases [2] and evaluating health care cost of stroke [3–5]. In 1998, a new ICD-9 procedure, code 99.10, was designated for injection or infusion of thrombolytic agents (http://www.cms.gov/ paymentsystems/icd9/fyadde.pdf. Accessed April 3, 2005). Current procedural terminology (CPT) designated codes for transcatheter therapy, infusion for thrombolysis (37201), transcatheter therapy, infusion for thrombolysis other than coronary (37202), and thrombolytic therapy for stroke (37195) (http://www.cms.gov/paymentsystems/icd9/fyadde. pdf. Accessed April 3, 2005). Use of these procedure codes may permit the utilization and outcome of thrombolysis at community and national levels using national and state
* Corresponding author. Tel.: 973-972-7852; fax: 973-972-9960. E-mail address: [email protected] (A.I. Qureshi). 0895-4356/06/$ – see front matter Ó 2006 Elsevier Inc. All rights reserved. doi: 10.1016/j.jclinepi.2006.01.004
databases [6,7]. We determine the accuracy of ICD-9-CM and CPT codes designated for thrombolysis by comparing records of hospital discharge data and a concurrent prospective registry. 2. Methods We identified patients treated with thrombolysis using the medical billing records for all patients admitted to the stroke center at a University Hospital between May 1, 2003 and June 30, 2004, with the primary diagnosis of ischemic stroke. A concurrent prospective Institutional Review Board approved database independently records baseline demographic and clinical characteristics and inhospital treatments (including thrombolysis) for all patients admitted with stroke. We used the ICD-9 procedure code 99.10 and CPT codes 37201 or 37202 (procedure code 37195 was not used in any patient) for our analysis. The accuracy of ICD-9 procedure code and CPT codes were determined by comparison with documentation of thrombolytic therapy in the prospective database. The sensitivity, specificity, positive predictive value, and negative predictive
A.I. Qureshi et al. / Journal of Clinical Epidemiology 59 (2006) 856–858
value of ICD-9 procedure code and CPT codes were calculated using standard methodologies [8]. The same values were also calculated using both procedure codes simultaneously. The actual probability of thrombolytic use in the presence or absence of designated ICD-9 procedure code or CPT code (the posttest probability) was calculated using Bayes’ equation [8]. In addition, the use of intravenous and intraarterial thrombolysis was separately analyzed to determine accuracy of ICD-9 procedure codes and CPT codes in identifying their respective utilization. 3. Results In the 13-month period, 420 patients were admitted to University Hospital with the diagnosis of stroke as determined from the prospective database. Ischemic strokes comprised of 88% (n 5 369) of these admissions. During this period, 49 patients (13.3%) received either intravenous and/or intraarterial therapy as determined by the prospective database. Using ICD-9 procedure code 99.10, 27 out of the 49 patients were identified as receiving thrombolytic treatment. In addition, there were five patients identified by ICD-9 procedure code 99.10 that never received thrombolytic therapy (false positives). Using CPT codes 37201/ 37202, we identified 24 of the 49 patients receiving thrombolytic treatment. Three false positives were identified using this method. Using presence of either ICD-9 or CPT codes, a total of 40 out of 49 patients were identified with eight false positives. Finally, presence of both ICD-9 and CPT codes identified 11 of the 49 patients with no false positives. The sensitivity, specificity, positive predictive value, and negative predictive value of ICD-9 procedure code 99.10 for identifying thrombolytic use was 55% [95% confidence interval (CI): 42–68%], 98% (95% CI: 96–99%), 84% (95% CI: 68–94%), and 93% (95% CI: 90–96%), respectively. The sensitivity, specificity, positive predictive value, and negative predictive value of CPT procedure codes 37201 and 37202 were 49% (95% CI: 36–63%), 99% (95% CI: 97–100%), 89% (95% CI: 71–97%), and 93% (95% CI: 89–95%), respectively. When the presence of either ICD-9 or CPT codes were used to identify use of thrombolysis, the sensitivity, specificity, positive predictive value, and negative predictive value were 82% (95% CI: 69–90%), 98% (95% CI: 95–99%), 83% (95% CI: 70– 92%), and 97% (95% CI: 95–99%), respectively. Finally, using the presence of both ICD-9 and CPT codes had a sensitivity, specificity, positive predictive value, and negative predictive value of 22% (95% CI: 13–36%), 100% (95% CI: 99–100%), 100% (95% CI: 70–100%), and 89% (95% CI: 86–92%), respectively. The posttest probability of presence or absence of ICD-9 and CPT codes is presented in Table 1. Intravenous thrombolysis was used as treatment in 35 of the 49 patients as determined from the prospective database. CPT codes and ICD-9 procedure codes identified 14
857
Table 1 Posttest probability of ICD-9 procedure code and CPT codes for identification of patients with ischemic stroke receiving thrombolysis Terminology
Presence of code
Absence of code
ICD-9 procedure code 99.10 CPT codes 37201 and 37202 ICD-9 procedure code OR CPT codes ICD-9 procedure code AND CPT codes
0.73 0.84 0.80
0.07 0.08 0.03
Not calculateda
Not calculateda
Abbreviations: ICD-9, International Classification of Diseases, 9th Revision; CPT, Current Procedural Terminology. a The likelihood ratio could not be calculated in the presence of a specificity of 100%.
(40%) and 19 (54%) of the 35 patients who received intravenous thrombolysis, respectively. ICD-9 and CPT codes identified 7 (50%) and 11 (78%) of the 14 patient who received intraarterial thrombolysis, respectively. Using the presence of either codes identified 27 (77%) of the 35 patients receiving intravenous and 13 (93%) of the 14 patients receiving intraarterial thrombolysis. Using the presence of both codes identified 6 (17%) of the 35 patients receiving intravenous and 5 (36%) of the 14 patients receiving intra-arterial thrombolysis. 4. Discussion We found that the sensitivity of either ICD-procedure code or CPT-procedure codes for identification of patients who received thrombolysis was low. The specificity appeared to be greater with the presence of both the ICD-9 and CPT procedure codes. The implications of the present results suggest that studies using the ICD-9 or CPT codes to estimate the utilization of thrombolysis in patients with ischemic stroke will result in underestimation of the actual rates. In our study, the frequency of thrombolytic use in patients with ischemic stroke ascertained by the ICD-9 procedure code or CPT codes used alone represents approximately half of the actual use. If patients are identified by the presence of either code, the actual number is expected to be approximately 25% greater. The high specificity suggested that patients identified with use of these procedure codes are likely to be patients who received thrombolysis. This may allow estimation of characteristics and cost associated with thrombolysis using national and state data sets. When patients were identified by the presence of either the ICD-9 or CPT-procedure code, the sensitivity increased to 82% with a specificity of 98%. This probably represents the best method of identifying patients with ischemic stroke who receive thrombolysis. Certain limitations need to be considered prior to interpretation of the results. We evaluated the accuracy of thrombolytic use in patients admitted to the hospital with ischemic stroke in one setting. The specificity may be lower if patients without ischemic stroke were included in the study population. The coding procedure is dependent upon the
858
A.I. Qureshi et al. / Journal of Clinical Epidemiology 59 (2006) 856–858
documentation provided in the charts. Our results are derived from patients treated at a university hospital with a dedicated stroke service. The results may not be generalizable to other settings because there may be differences related in documentation. Further studies are required to determine the accuracy of ICD-9 procedure and CPT codes to identify utilization of thrombolysis in other settings. With a better knowledge of the accuracy of these codes, a more accurate interpretation of estimates derived from regional and national databases may be possible. The importance of appropriate analyses of data from these databases to estimate thrombolytic use in various populations, regions, and settings, and trends over time cannot be undermined. References [1] Health Care Financing Administration. International classification of diseases, 9th revision: Department of Health and Human Services, 1989. Report No.: DHHS Publication No. (PHS):89–1260.
[2] Leibson CL, Naessens JM, Brown RD, Whisnant JP. Accuracy of hospital discharge abstracts for identifying stroke. Stroke 1994;25: 2348–55. [3] Ellekjaer H, Holmen J, Indredavik B, Terent A. Epidemiology of stroke in innherred, Norway, 1994 to 1996. Incidence and 30-day casefatality rate. Stroke 1997;28:2180–4. [4] Whisnant JP, Melton LJ 3rd, Davis PH, O’Fallon WM, Nishimaru K, Schoenberg BS. Comparison of case ascertainment by medical record linkage and cohort follow-up to determine incidence rates for transient ischemic attacks and stroke. J Clin Epidemiol 1990;43:791–7. [5] Qureshi AI, Suri MFK, Nasar A, He W, Kirmani JF, Divani AA, Prestigiacomo CJ, Low RB. Thrombolysis for ischemic stroke in the United States. Data from National Hospital Discharge Survey 1999–2001. Neurosurgery 2005;57:647–54. [6] Wennberg JE, Roos N, Sola L, Schori A, Jaffe R. Use of claims data systems to evaluate health care outcomes. Mortality and reoperation following prostatectomy. JAMA 1987;257:933–6. [7] Qureshi AI. Ten years of advances in neuroendovascular procedures. J Endovasc Ther 2004;11(Suppl 2):II1–4. [8] Anonymous. Interpretation of diagnostic data: 5. How to do it with simple maths. Can Med Assoc J 1983;129:947–54.
International classification of diseases and current procedural terminology codes underestimated thrombolytic use for ischemic stroke Adnan I. Qureshi*, Pansy Harris-Lane, Faisal Siddiqi, Jawad F. Kirmani Epidemiological and Outcomes Research Division, Zeenat Qureshi Stroke Research Center, Department of Neurology and Neurosciences, University of Medicine and Dentistry of New Jersey, 90 Bergen Streeet, DOC-8100, Newark, NJ 07103, USA Accepted 7 January 2006
Abstract Background and Objective: To determine the accuracy of recently introduced International Classification of Diseases Ninth Revision (ICD-9) procedure and Current Procedural Terminology (CPT) codes designed for injection or infusion of thrombolytic agents. Materials and Methods: We determined the accuracy of ICD-9 procedure code 99.10 and CPT codes 37201, 37202 for use of thrombolysis in ischemic stroke by comparing procedure codes of University Hospital discharge data with a concurrent prospective registry. Results: Of the 369 ischemic stroke patients, 49 (13.3%) received either intravenous and/or intraarterial thrombolysis. The sensitivity and specificity for ICD-9 procedure code 99.10 was 55% and 98% and CPT procedure code 37201 and 37202 was 49% and 99%. Identification by either ICD-9 codes or CPT codes yielded a high sensitivity and specificity of 82% and 98%. Conclusions: The use of ICD-9 and CPT codes alone may underestimate the use of thrombolytics using national and regional database. Best results are achieved when a combination of ICD-9 and CPT codes are used to identify the use of thrombolytics. Ó 2006 Elsevier Inc. All rights reserved. Keywords: Current Procedural Terminology (CPT); International Classification of Diseases Ninth Revision (ICD-9); Ischemic Stroke; Stroke; Thrombolysis; Thrombolytics
1. Introduction Hospital discharge diagnoses are routinely coded using International Classification of Diseases, 9th Revision (ICD-9) [1]. Previous studies have validated ICD-9 diagnoses codes for identification of incident cases [2] and evaluating health care cost of stroke [3–5]. In 1998, a new ICD-9 procedure, code 99.10, was designated for injection or infusion of thrombolytic agents (http://www.cms.gov/ paymentsystems/icd9/fyadde.pdf. Accessed April 3, 2005). Current procedural terminology (CPT) designated codes for transcatheter therapy, infusion for thrombolysis (37201), transcatheter therapy, infusion for thrombolysis other than coronary (37202), and thrombolytic therapy for stroke (37195) (http://www.cms.gov/paymentsystems/icd9/fyadde. pdf. Accessed April 3, 2005). Use of these procedure codes may permit the utilization and outcome of thrombolysis at community and national levels using national and state
* Corresponding author. Tel.: 973-972-7852; fax: 973-972-9960. E-mail address: [email protected] (A.I. Qureshi). 0895-4356/06/$ – see front matter Ó 2006 Elsevier Inc. All rights reserved. doi: 10.1016/j.jclinepi.2006.01.004
databases [6,7]. We determine the accuracy of ICD-9-CM and CPT codes designated for thrombolysis by comparing records of hospital discharge data and a concurrent prospective registry. 2. Methods We identified patients treated with thrombolysis using the medical billing records for all patients admitted to the stroke center at a University Hospital between May 1, 2003 and June 30, 2004, with the primary diagnosis of ischemic stroke. A concurrent prospective Institutional Review Board approved database independently records baseline demographic and clinical characteristics and inhospital treatments (including thrombolysis) for all patients admitted with stroke. We used the ICD-9 procedure code 99.10 and CPT codes 37201 or 37202 (procedure code 37195 was not used in any patient) for our analysis. The accuracy of ICD-9 procedure code and CPT codes were determined by comparison with documentation of thrombolytic therapy in the prospective database. The sensitivity, specificity, positive predictive value, and negative predictive
A.I. Qureshi et al. / Journal of Clinical Epidemiology 59 (2006) 856–858
value of ICD-9 procedure code and CPT codes were calculated using standard methodologies [8]. The same values were also calculated using both procedure codes simultaneously. The actual probability of thrombolytic use in the presence or absence of designated ICD-9 procedure code or CPT code (the posttest probability) was calculated using Bayes’ equation [8]. In addition, the use of intravenous and intraarterial thrombolysis was separately analyzed to determine accuracy of ICD-9 procedure codes and CPT codes in identifying their respective utilization. 3. Results In the 13-month period, 420 patients were admitted to University Hospital with the diagnosis of stroke as determined from the prospective database. Ischemic strokes comprised of 88% (n 5 369) of these admissions. During this period, 49 patients (13.3%) received either intravenous and/or intraarterial therapy as determined by the prospective database. Using ICD-9 procedure code 99.10, 27 out of the 49 patients were identified as receiving thrombolytic treatment. In addition, there were five patients identified by ICD-9 procedure code 99.10 that never received thrombolytic therapy (false positives). Using CPT codes 37201/ 37202, we identified 24 of the 49 patients receiving thrombolytic treatment. Three false positives were identified using this method. Using presence of either ICD-9 or CPT codes, a total of 40 out of 49 patients were identified with eight false positives. Finally, presence of both ICD-9 and CPT codes identified 11 of the 49 patients with no false positives. The sensitivity, specificity, positive predictive value, and negative predictive value of ICD-9 procedure code 99.10 for identifying thrombolytic use was 55% [95% confidence interval (CI): 42–68%], 98% (95% CI: 96–99%), 84% (95% CI: 68–94%), and 93% (95% CI: 90–96%), respectively. The sensitivity, specificity, positive predictive value, and negative predictive value of CPT procedure codes 37201 and 37202 were 49% (95% CI: 36–63%), 99% (95% CI: 97–100%), 89% (95% CI: 71–97%), and 93% (95% CI: 89–95%), respectively. When the presence of either ICD-9 or CPT codes were used to identify use of thrombolysis, the sensitivity, specificity, positive predictive value, and negative predictive value were 82% (95% CI: 69–90%), 98% (95% CI: 95–99%), 83% (95% CI: 70– 92%), and 97% (95% CI: 95–99%), respectively. Finally, using the presence of both ICD-9 and CPT codes had a sensitivity, specificity, positive predictive value, and negative predictive value of 22% (95% CI: 13–36%), 100% (95% CI: 99–100%), 100% (95% CI: 70–100%), and 89% (95% CI: 86–92%), respectively. The posttest probability of presence or absence of ICD-9 and CPT codes is presented in Table 1. Intravenous thrombolysis was used as treatment in 35 of the 49 patients as determined from the prospective database. CPT codes and ICD-9 procedure codes identified 14
857
Table 1 Posttest probability of ICD-9 procedure code and CPT codes for identification of patients with ischemic stroke receiving thrombolysis Terminology
Presence of code
Absence of code
ICD-9 procedure code 99.10 CPT codes 37201 and 37202 ICD-9 procedure code OR CPT codes ICD-9 procedure code AND CPT codes
0.73 0.84 0.80
0.07 0.08 0.03
Not calculateda
Not calculateda
Abbreviations: ICD-9, International Classification of Diseases, 9th Revision; CPT, Current Procedural Terminology. a The likelihood ratio could not be calculated in the presence of a specificity of 100%.
(40%) and 19 (54%) of the 35 patients who received intravenous thrombolysis, respectively. ICD-9 and CPT codes identified 7 (50%) and 11 (78%) of the 14 patient who received intraarterial thrombolysis, respectively. Using the presence of either codes identified 27 (77%) of the 35 patients receiving intravenous and 13 (93%) of the 14 patients receiving intraarterial thrombolysis. Using the presence of both codes identified 6 (17%) of the 35 patients receiving intravenous and 5 (36%) of the 14 patients receiving intra-arterial thrombolysis. 4. Discussion We found that the sensitivity of either ICD-procedure code or CPT-procedure codes for identification of patients who received thrombolysis was low. The specificity appeared to be greater with the presence of both the ICD-9 and CPT procedure codes. The implications of the present results suggest that studies using the ICD-9 or CPT codes to estimate the utilization of thrombolysis in patients with ischemic stroke will result in underestimation of the actual rates. In our study, the frequency of thrombolytic use in patients with ischemic stroke ascertained by the ICD-9 procedure code or CPT codes used alone represents approximately half of the actual use. If patients are identified by the presence of either code, the actual number is expected to be approximately 25% greater. The high specificity suggested that patients identified with use of these procedure codes are likely to be patients who received thrombolysis. This may allow estimation of characteristics and cost associated with thrombolysis using national and state data sets. When patients were identified by the presence of either the ICD-9 or CPT-procedure code, the sensitivity increased to 82% with a specificity of 98%. This probably represents the best method of identifying patients with ischemic stroke who receive thrombolysis. Certain limitations need to be considered prior to interpretation of the results. We evaluated the accuracy of thrombolytic use in patients admitted to the hospital with ischemic stroke in one setting. The specificity may be lower if patients without ischemic stroke were included in the study population. The coding procedure is dependent upon the
858
A.I. Qureshi et al. / Journal of Clinical Epidemiology 59 (2006) 856–858
documentation provided in the charts. Our results are derived from patients treated at a university hospital with a dedicated stroke service. The results may not be generalizable to other settings because there may be differences related in documentation. Further studies are required to determine the accuracy of ICD-9 procedure and CPT codes to identify utilization of thrombolysis in other settings. With a better knowledge of the accuracy of these codes, a more accurate interpretation of estimates derived from regional and national databases may be possible. The importance of appropriate analyses of data from these databases to estimate thrombolytic use in various populations, regions, and settings, and trends over time cannot be undermined. References [1] Health Care Financing Administration. International classification of diseases, 9th revision: Department of Health and Human Services, 1989. Report No.: DHHS Publication No. (PHS):89–1260.
[2] Leibson CL, Naessens JM, Brown RD, Whisnant JP. Accuracy of hospital discharge abstracts for identifying stroke. Stroke 1994;25: 2348–55. [3] Ellekjaer H, Holmen J, Indredavik B, Terent A. Epidemiology of stroke in innherred, Norway, 1994 to 1996. Incidence and 30-day casefatality rate. Stroke 1997;28:2180–4. [4] Whisnant JP, Melton LJ 3rd, Davis PH, O’Fallon WM, Nishimaru K, Schoenberg BS. Comparison of case ascertainment by medical record linkage and cohort follow-up to determine incidence rates for transient ischemic attacks and stroke. J Clin Epidemiol 1990;43:791–7. [5] Qureshi AI, Suri MFK, Nasar A, He W, Kirmani JF, Divani AA, Prestigiacomo CJ, Low RB. Thrombolysis for ischemic stroke in the United States. Data from National Hospital Discharge Survey 1999–2001. Neurosurgery 2005;57:647–54. [6] Wennberg JE, Roos N, Sola L, Schori A, Jaffe R. Use of claims data systems to evaluate health care outcomes. Mortality and reoperation following prostatectomy. JAMA 1987;257:933–6. [7] Qureshi AI. Ten years of advances in neuroendovascular procedures. J Endovasc Ther 2004;11(Suppl 2):II1–4. [8] Anonymous. Interpretation of diagnostic data: 5. How to do it with simple maths. Can Med Assoc J 1983;129:947–54.