Background/Purpose:  The information on the population-based prevalence of Psoriatic Arthritis (PsA) is limited. Large population-based databases provide an opportunity to study the epidemiology of PsA, however, strict validation procedures for case ascertainment are required. We aimed to examine the validity of a diagnostic code for PsA in Clalit Health Services (CHS) database in Israel and to estimate its point prevalence in the general population.

Methods:  CHS database, Israel’s largest public health fund serving 4.3 million enrollees (>50% of Israel’s population), has real-time input from pharmaceutical, medical and administrative operating systems. CHS database was searched for all individuals who received their initial diagnostic code of PsA (ICD-9 code 696.0) in 2014. Cases were divided according to the type of specialist (rheumatologists, family physicians, dermatologists, orthopedics) who assigned the diagnostic code of PsA.. Approximately 25% of the cases in each subspecialty group were selected at random for the validation of a diagnostic code of PsA. All medical records of these patients were thoroughly read by two rheumatologists. Based on this information a decision was made whether the PsA diagnosis was 1) definite/probable PsA; 2) not PsA; 3) no data to verify the diagnosis of PsA. We calculated the positive predicted value (PPV) and the 95% confidence interval in each group. Several algorithms were examined to determine the method resulting in the highest PPV. The sensitivity and specificity for the selected algorithm were calculated and the point prevalence of PsA in the general population and its 95% confidence interval (CI) were estimated.

Results: 869 individuals who received a diagnosis of PsA in 2014 were identified. 205 cases were selected for validation based on the specialty of the physician who assigned the diagnosis. The proportion of ICD-9 codes that could be confirmed by reviewing the medical records was 94%. The PPVs for a diagnostic code assigned by a rheumatologist or given during hospitalization was: 90.5% (95% CI 82.3%, 95.3%), orthopedics 18.2% (95% CI 3.2%, 52.2%) dermatologists 13.3% (95% CI 2.3%, 41.6%) and family physicians 50% (95% CI 29.6%, 70.3%). The selected algorithm comprised the PsA code assigned by a rheumatologist, or a permanent diagnosis code assigned by a family physician combined with use of DMARDs, or PsA code given during hospitalization. This algorithm had sensitivity and specificity of 88.7% and 88.1%, respectively. Using the validated algorithm, 3874 PsA patients were identified among a population of 4,296,000 enrollees in the CHS database, reflecting prevalence of 90 per 100,000 (95% CI 87, 93 per 100,000).

Conclusion:  Data within electronic medical records can be used to accurately identify patients with PsA. The estimated prevalence of PsA in the general population in Israel is 0.09%. This figure is consistent with other population-based estimates.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/validity-of-diagnostic-codes-and-point-prevalence-of-psoriatic-arthritis-in-israel-a-population-based-study/