Study Finds CPT Codes Superior to ICD Codes for Quantifying Patients’ Skin Cancers

International Classification of Disease (ICD) codes were a poor proxy measure for the number of skin cancers per patient, according to results of a retrospective cohort study published in JAMA Dermatology. Current Procedural Terminology (CPT) codes were a better proxy measure for the total number of skin cancers per patient, accounting for over 75% of the variability in the number of cancers, the researchers wrote.

Despite keratinocyte cancers being the most common malignant neoplasms among White populations worldwide, they are often not included in cancer registries. In addition, “when data are available, most studies have focused on identifying factors associated with the development of any skin cancer, but many patients develop numerous skin cancers, often with medical records scattered across different health care systems,” the authors explained.

Because having multiple skin cancers is associated with an increased risk for some internal malignant neoplasms and knowledge of the conditions could help providers understand which transplant recipients will respond to prevention treatments, researchers sought to assess the association of the number of CPT and ICD codes with the true number of skin cancers among patients.

Two sets of patients were included in the final analyses, including Vanderbilt University Medical Center’s (VUMC’s) clinical database of patients seen between 2008 and 2018 who had an ICD or CPT code for skin cancer. The second set included patients seen at the center during this time who had at least 1 pathology report showing a skin cancer.

Of the 35,901 patients included, the mean age was around 70 years, while the majority (56.8%) of patients were men and 88.1% where White.

Analyses revealed:

• 6307 individuals had at least 1 ICD or CPT code or pathology report for a skin cancer, of whom 5688 patients had both a CPT code related to skin malignancy and a histologically verified skin cancer
• There was a strong linear correlation between the number of CPT codes and pathology records (r = 0.87)
• There was a poor correlation between the number of ICD codes and pathology records (r = 0.22)
• A strong correlation existed between nonmelanoma skin cancer (NMSC) same-day events and pathologically confirmed NMSC (r = 0.86), but there was a weak correlation for melanoma (r = 0.55) and Merkel cell carcinoma (r = 0.58)
• The positive predictive value was strong for NMSC, squamous cell carcinoma, and basal cell carcinoma (> 0.9 for each) but less so for melanoma and Merkel cell carcinoma

“We observed that the number of CPT codes was strongly correlated with the total number of histologically verified skin cancers, although most patients had a more than 30% discrepancy in the total counts,” the authors wrote.

The researchers were unable to count CPT codes for skin cancers treated topically, with systemic chemotherapy, or with radiation, or those cleared by biopsy. Incidence or prevalence estimates cannot be derived from the findings as the analysis was not a population-based cohort study.

Reference

Anand N, Edwards L, Baker LX, Chren M, Wheless L. Validity of using billing codes from electronic health records to estimate skin cancer counts. JAMA Dermatol. Published online August 11, 2021. doi:10.1001/jamadermatol.2021.2856