Validity of the recorded International Classification of Diseases, 10th edition diagnoses codes of bone metastases and skeletal-related events in breast and prostate cancer patients in the Danish National Registry of Patients

OBJECTIVE The clinical history of bone metastases and skeletal-related events (SREs) secondary to cancers is not well understood. In support of studies of the natural history of bone metastases and SREs in Danish prostate and breast cancer patients, we estimated the sensitivity and specificity of hospital diagnoses for bone metastases and SREs (ie, radiation therapy to the bone, pathological or osteoporotic fractures, spinal cord compression and surgery to the bone) in a nationwide medical registry in Denmark. STUDY DESIGN AND SETTING In North Jutland County, Denmark, we randomly sampled 100 patients with primary prostate cancer and 100 patients with primary breast cancer diagnoses from the National Registry of Patients (NRP), during the period January 1st, 2000 to December 31st, 2000 and followed them for up to five years after their cancer diagnosis. We used information from medical chart reviews as the reference for estimating sensitivity, and specificity of the NRP International Classification of Diseases, 10th edition (ICD-10) coding for bone metastases and SRE diagnoses. RESULTS For prostate cancer, the overall sensitivity of bone metastases or SRE coding in the NRP was 0.54 (95% confidence interval [CI]: 0.39-0.69), and the specificity was 0.96 (95% CI: 0.87-1.00). For breast cancer, the overall sensitivity of bone metastases or SRE coding in the NRP was 0.58 (95% CI: 0.34-0.80), and the specificity was 0.95 (95% CI: 0.88-0.99). CONCLUSION We measured the validity of ICD-10 coding in the Danish NRP for bone metastases and SREs in prostate and breast cancer patients and found it has adequate sensitivity and high specificity. The NRP remains a valuable tool for clinical epidemiological studies of bone metastases and SREs.