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

Abstract

Few population-based studies have reported the prevalence of psoriatic disease. We validated computerized diagnoses to estimate the prevalence of psoriasis and psoriatic arthritis. 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. 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. 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.