Endocrine Abstracts

JOINT2884

Context: A recent head-to-head multicenter trial established the superiority of hypertonic saline-stimulated copeptin in the diagnosis of vasopressin deficiency (AVP-D), with the arginine test presenting suboptimal performance. Nevertheless, the latter is less costly, better tolerated and easier to perform. We tried to enhance its performance by including other parameters on top of copeptin levels.

Methods: We conducted a retrospective analysis of arginine tests performed at our Unit for suspected AVP-D. Clinical, biochemical and radiological findings were collected. Final diagnosis was defined based on a revision of clinical picture, performed tests and follow-up data.

Results: We considered 19 patients, 8 of them presenting a final diagnosis of AVP-D from different causes (42%). Copeptin response to arginine was flattened in AVP-D patients (AUC 4.48 vs 6.97, P = 0.11) but, irrespectively of the indexes and thresholds used, it could not provide good discrimination from primary polydipsia (PP). The best performing index was copeptin level at 90 minutes (cut-off 3.45 pmol/l, sensitivity 87.5%, specificity 63.6%, diagnostic accuracy 73.7%, ROC-AUC 0.773). AVP-D patients at the end of the arginine test presented lower urinary osmolarity (UOsm) and higher plasma osmolarity and sodium (Na) levels. The latter was the best predictor of AVP-D (cut-off 141.5 mmol/l, sensitivity 87.5%, specificity 100%, diagnostic accuracy 94.7%, ROC-AUC 0.989). When combining multiple parameters, we were able to obtain perfect discrimination between AVP-D and PP in our cohort. In a multistep approach, a final Na above 142 or below 140 mmol/l identified alone AVP-D and PP respectively, while in case of intermediate values a copeptin peak <4.1 pmol/l or a final UOsm <428 mOsm/kg correctly diagnosed AVP-D (overall diagnostic accuracy 100%). We also obtained via logistic regression formulas to derive a corrected sodium value providing a diagnostic accuracy of 100% (cut-offs: 138.8 mmol/l based on final Na and peak copeptin; 138 mmol/l based on final Na and UOsm).

Discussion: In our cohort, the use of multiple parameters following arginine stimulation could enhance the test performance up to a complete discrimination between AVP-D and PP. Interestingly, this result could be obtained also without copeptin measurement. Our study has nevertheless various limitations, the most important ones being the small sample analysed and the non-use of hypertonic saline-stimulated copeptin. Larger studies with the use of current gold standard test for comparison are needed to evaluate the replicability of our findings.