Endocrine Abstracts

Introduction: Water deprivation testing (WDT) is considered the gold standard test in differentiating between craniogenic diabetes insipidus (DI), nephrogenic DI and primary polydipsia. However, it requires day case admission for monitoring of sodium and osmolality. Copeptin, derived from pre-provasopressin, is secreted in an equimolar amount with arginine vasopressin and has a potential role in facilitating the diagnosis of DI and reducing the need for WDT. Copeptin was gradually introduced at Royal Derby Hospital in 2019 as a screening test for DI. Here we discuss our experience and the impact it has had on our protocol for the investigation of DI.

Methods: All patients (13) who had received a copepetin test as part of their work up for DI were selected. The results of serum/urinary osmolality tests and any WDT were also analysed. The impact of copeptin on the final diagnosis of DI were reviewed and discussed at the local joint Endocrinology & Biochemistry meeting.

Results: Of the 13 patients analysed, only two copeptin results proved difficult to interpret as there was no associated urine osmolality. Of the 11 which could be interpreted, WDT was avoided in 3 patients with only 2 progressing to testing following the screening test. A further 6 WDT tests could potentially have been avoided if the copeptin level had been taken following an overnight fast.

Discussion: WDT is a time consuming, logistically challenging and unpleasant test for any patient with DI to undergo. Furthermore, the Covid-19 pandemic has made day case admissions challenging. By introducing an overnight fasting copeptin test (or >4hrs in very symptomatic cases) into our local protocol we were able to continue to investigate patients for DI during the Covid-19 pandemic whilst reducing the need for water deprivation testing.