To assess the accuracy in clinical use of the International Classification of Disease-10 (ICD-10) code G20 in identifying patients with idiopathic Parkinson’s Disease (PD) among White and African American races.

The ICD-10 code G20 is used for hemiparkinsonism, idiopathic PD, paralysis agitans, parkinsonism or PD not otherwise specified, and primary parkinsonism. Prior studies have evaluated the validity of ICD codes in identifying PD and found a positive predictive value (PPV) ranging from 44-83%. No studies have evaluated the effect of race on correctly identifying PD with the ICD-10 code G20.

A retrospective chart review was performed on all patients seen at the University of Alabama at Birmingham between 1/1/16 and 1/1/18 with the ICD-10 diagnosis code of G20.  A random sample of 50 patients that self-identified as White race and 50 patients that self-identified as African American race was used for analysis. Categorical variables were compared using a chi-squared test. Data was analyzed using SPS version 25.0 (IBM Corp., Armonk, NY). Statistical significance was defined as p<0.05.

The diagnosis code G20 correctly identified idiopathic PD patients more frequently in White versus African American patients (70% vs 46%, respectively, p=0.026). Atypical parkinsonism, essential tremor, an unclear diagnosis, and other diagnoses were found at similar frequencies within the White and African American groups. African American patients were more likely to have no documentation of a PD diagnosis in the chart (20% vs 4%) or to have drug-induced parkinsonism (8% vs 0%) than White patients (p=0.038).

In this retrospective chart review, G20 had a significantly lower PPV for accurately identifying idiopathic PD in African Americans than in Whites. A significant number of the African Americans coded as G20 did not have documentation of a PD diagnosis in the chart, and the reason for this discrepancy warrants further investigation.