The Time of the Hypertonic Saline Infusion Test for the Diagnosis of AVP Deficiency Can Be Shortened With LC-MS/MS

Context In clinical practice, plasma arginine vasopressin (AVP) concentrations have been measured with a radioimmunoassay (RIA). However, RIAs have limitations, such as long turnaround time, use of radioisotopes, and restricted antibody availability. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) offers a promising alternative, eliminating the need for radioisotopes and antibodies while providing faster results. Objective This study aimed to assess the usefulness of LC-MS/MS for measuring plasma AVP concentrations in diagnosing AVP deficiency (AVP-D). Methods We included 16 patients with AVP-D and 28 controls. All participants underwent a hypertonic saline infusion test (HST), during which plasma AVP concentrations were measured using RIA and LC-MS/MS. Regression coefficients (gradients) for serum sodium vs plasma AVP concentrations were evaluated at 90 and 120 minutes, and receiver-operating characteristic analyses were performed based on these regression coefficients. Results The area under the receiver-operating characteristic curve at 90 minutes was 0.97 (95% CI, 0.83-1.00) and 0.93 (95% CI, 0.80-0.98) for LC-MS/MS and RIA, respectively. A regression gradient cutoff with optimal values distinguished AVP-D from controls with a sensitivity of 100% in LC-MS/MS and RIA, whereas the specificity was 96% and 81% with LC-MS/MS and RIA, respectively. Sensitivity or specificity did not differ in 120 minutes between the 2 methods. Conclusion LC-MS/MS demonstrated superior diagnostic accuracy for AVP-D at 90 minutes of HST, indicating that the HST time can be shortened from 120 to 90 minutes by measuring AVP with LC-MS/MS. Clinical trial registration The study was registered with the University Hospital Medical Information Network (UMIN) registry (UMIN000043023).