In a major advancement for endocrinology and nephrology, an international team of researchers has developed a validated diagnostic score capable of distinguishing arginine vasopressin (AVP) deficiency—also known as central diabetes insipidus—from primary polydipsia. This distinction has historically posed a significant clinical challenge due to overlapping symptoms and the absence of reliable baseline diagnostic tools at initial consultation. The analysis was published in The Lancet Diabetes and Endocrinology. 

The new score, developed from two large multicenter diagnostic studies (CODDI and CARGOx), incorporates a stepwise assessment beginning with simple basal laboratory parameters—such as plasma sodium, plasma osmolality, and copeptin levels—along with specific clinical symptoms and medical history. A novel scoring formula was then used to assign weighted values to these parameters, enabling clinicians to stratify patients for either immediate treatment or further testing.

The score was derived from 141 patients and validated in an independent cohort of 158 patients across tertiary centers in Switzerland, Germany, Brazil, the UK, Italy, and the Netherlands. Among the participants, 128 were confirmed to have AVP deficiency, and 171 had primary polydipsia, based on results from the hypertonic saline test, considered the current diagnostic standard.

Key findings from the validation cohort showed that basal plasma sodium levels above 145 mmol/L had 100% specificity for AVP deficiency, while sodium levels below 135 mmol/L or copeptin levels above 5.6 pmol/L had 100% specificity for primary polydipsia. When applied as a diagnostic score, an area under the curve (AUC) of 91% was achieved, with a cutoff of more than 441 points yielding 86% diagnostic accuracy. High-specificity thresholds of >461 and <415 points were able to identify AVP deficiency and primary polydipsia, respectively, with 93% specificity in each case.

Notably, this scoring model allowed accurate diagnosis in 75% of the 299 patients without resorting to complex dynamic stimulation tests. For the remaining intermediate cases, the score still significantly enhanced clinical decision-making.
The implementation of this stepwise diagnostic protocol is expected to streamline diagnosis, accelerate treatment initiation, and reduce the need for resource-intensive testing, ultimately improving outcomes for patients with polyuric disorders.