Concordance Between ICD-10 Codes and Clinical Diagnosis of Hypoparathyroidism in Sweden

INTRODUCTION: Chronic hypoparathyroidism is a rare disorder. The disease is characterized by low serum calcium, high serum phosphate, and deficient production of parathyroid hormone. The most common etiology is unintentional damage and intentional removal to the parathyroid glands during anterior neck surgery. Other causes include genetic disorders and autoimmune diseases. Knowledge about the epidemiology of chronic hypoparathyroidism is sparse and the prevalence in Sweden is unknown. It is of importance to know the validity of the registers used to study the epidemiology of hypoparathyroidism in Sweden. The purpose of this study was to validate the International Classification of Diseases - 10th revision (ICD-10) diagnosis of hypoparathyroidism in the Swedish National Patient Register. METHODS: We included patients with the ICD-10 diagnosis of hypoparathyroidism that were found in the Swedish National Patient Register during 2004 to 2016. Through the unique national registration number assigned to all Swedish inhabitants, we could link this information to the Swedish Prescribed Drug Register. We included patients with an ICD-10 diagnosis for hypoparathyroidism and on concurrent conventional treatment for the disease. The validation of the diagnosis was assessed through review of medical records of 120 patients. RESULTS: A total of 958 patients, 70% women (n=671) and 30% men (n=287) met the inclusion criteria. In total, 120 randomly chosen medical records were reviewed and 109 cases were confirmed. This corresponds to an overall positive predictive value of 91%. CONCLUSION: The validity of the ICD-10 diagnosis of hypoparathyroidism in the Swedish National Patient Register is high and the register is a reliable source for further research. There is a risk of miscoding when assigning an ICD-code to the medical records. We urge clinicians to be aware of this risk, especially the risk of mix-ups with the more common diagnosis of hyperparathyroidism.