The following is a summary of “Arginine or Hypertonic Saline–Stimulated Copeptin to Diagnose AVP Deficiency,” published in the November 2023 issue of Psychiatry by Refardt et al.

Researchers conducted a retrospective study to compare the diagnostic accuracy of arginine-stimulated copeptin and hypertonic saline–stimulated copeptin in distinguishing between arginine vasopressin (AVP) deficiency and primary polydipsia, considering the simplicity of the test protocol and the need for close sodium monitoring.

They initiated an international, non-inferiority trial involving adult patients exhibiting polydipsia and hypotonic polyuria or having a confirmed AVP deficiency diagnosis. These patients underwent diagnostic evaluation with hypertonic-saline stimulation on one occasion and arginine stimulation on another. Using clinical information, treatment response, and test results, two endocrinologists independently determined the final diagnosis of AVP deficiency or primary polydipsia. The primary outcome was overall diagnostic accuracy, with prespecified copeptin cutoff values of 3.8 picomoles per liter following 60 minutes for arginine and 4.9 picomoles per liter once the sodium level exceeded 149 millimoles per liter for hypertonic saline.

The results showed that of 158 patients undergoing both tests, 69 (44%) were diagnosed with AVP deficiency and 89 (56%) with primary polydipsia. The diagnostic accuracy was 74.4% (95% CI: 67.0 to 80.6) for arginine-stimulated copeptin and 95.6% (95% CI: 91.1 to 97.8) for hypertonic saline–stimulated copeptin, with an estimated difference of -21.2 percentage points (95% CI: -28.7 to -14.3). Adverse events were generally mild for both tests, and 72% of patients preferred arginine testing over hypertonic saline. A copeptin level below 3.0 picomoles per liter with arginine stimulation resulted in an AVP deficiency diagnosis with a specificity of 90.9% (95% CI: 81.7 to 95.7), whereas levels above 5.2 picomoles per liter suggested primary polydipsia with a specificity of 91.4% (95% CI: 83.7 to 95.6).

Investigators concluded that hypertonic saline-stimulated copeptin in adults with polyuria polydipsia syndrome provided a more accurate AVP deficiency diagnosis than arginine-stimulated copeptin.

Source: nejm.org/doi/full/10.1056/NEJMoa2306263