Validity of diagnostic codes and prevalence of psoriasis and psoriatic arthritis in a managed care population, 1996-2009

Background Few population-based studies have reported the prevalence of psoriatic disease. Objective We validated computerized diagnoses to estimate the prevalence of psoriasis and psoriatic arthritis. Method We identified adults with ≥1 ICD-9 diagnosis codes of 696.0 (psoriatic arthritis) or 696.1 (psoriasis) in clinical encounter data during 1996–2009 and used chart review to confirm the diagnoses in random samples of patients. We then used the best performing case-finding algorithms to estimate the point prevalence of psoriasis and psoriatic arthritis. Results The number of persons with a diagnosis for psoriasis (ICD-9 code 696.1) was 87 827. Chart review of a random sample of 101 cases with at least one dermatologist-rendered psoriasis code revealed a positive predictive value (PPV) of 90% (95% CI, 83–95) with sensitivity of 88% (95% CI, 80–93). Psoriatic arthritis (code 696.0) was recorded for 5187 patients, with the best performing algorithm requiring ≥2 diagnoses recorded by a rheumatologist or ≥1 diagnosis recorded by a rheumatologist together with ≥1 psoriasis diagnoses recorded by a dermatologist; the PPV was 80% (95% CI, 70–88) with sensitivity 73% (95% CI, 63–82). Among KPNC adults, the point prevalence of psoriasis, with or without psoriatic arthritis, was 939 (95% CI, 765–1142) per 100 000, and the overall prevalence of psoriatic arthritis, with or without psoriasis, was 68 (95% CI, 54–84) per 100 000. Conclusion Within an integrated health care delivery system, the use of computerized diagnoses rendered by relevant disease specialists is a valid method for identifying individuals with psoriatic disease. Copyright © 2013 John Wiley & Sons, Ltd.