Registry versus claims-based index dates for studies of cancer diagnosis in administrative data

Studies of healthcare encounters leading to cancer diagnosis have increased over recent years. While some studies examine healthcare utilization before the cancer registry date of diagnosis, relevant pre-diagnosis interactions are not always immediately prior to this date due to date abstraction guidelines. We evaluated agreement of a registry date with a claims-based index and examined Emergency Department (ED) involvement in cancer diagnosis as an example of possible pre-diagnostic healthcare misclassification that could arise from improper date choice.

We implemented an algorithm to define a claims-based index as the date of the earliest International Classification of Diseases code for the cancer in Medicare and estimated agreement with the date of diagnosis from a North Carolina registry for patients diagnosed aged 66 or older with 16 cancer types from 2008 to 2017 (n = 92,056). We then classified whether each cancer was initially diagnosed through care originating in the ED using each date.

The index date was identical to the cancer registry date for 47% of patients and preceded the registry date for 28%, with extent of agreement varying by cancer- and patient-specific characteristics. Agreement in ED-involved diagnosis classification using each date varied by cancer site, with sensitivity of classifications using the registry date relative to the index having a minimum of 86% for prostate and kidney cancer.

Studies assessing healthcare utilization proximal to cancer diagnosis should carefully consider the relevant assessment window and be aware that the use of cancer registry versus claims-based dates may impact variable classification.