The 3% hypertonic saline infusion test for the differential diagnosis of diabetes insipidus and primary polydipsia: assessment of diagnostic accuracy

AIM: assessment of the diagnostic accuracy of a 3% hypertonic saline infusion test in relation to a set of clinical and laboratory data (including a water deprivation test and MRI data) for differential diagnoses of diabetes insipidus (DI) and primary polydipsia (PP). METHODS: An interventional cross-sectional study was carried out at Endocrinology Research Centre From September 2021 to September 2023 ninety patients with polyuria-polydipsia syndrome were included. In order to assess the diagnostic characteristics, all the subjects underwent two tests with osmotic stimulation: a 3% hypertonic saline infusion test and a water deprivation test. Adverse events were assessed. RESULTS: Based on the results of clinical, anamnestic, laboratory and instrumental data, and the results of a water deprivation test, a final diagnosis of DI was made in 48 (53%) patients and PP in 42 (47%) patients. The agreement between the two samples is significant — Kappa = 0.823, 95% CI (0.707, 0.939). The operational parameters of the 3% hypertonic saline infusion test are: sensitivity 98% (95% CI: 89%; 100%); specificity 98% (95% CI: 87%; 100%), positive and negative predictive values 98% (95% CI: 89%–100%) and 98% (95% CI: 87%–100%). Respectively. Chills occurred significantly more often (31% vs. 12%), and dizziness and headache were more pronounced during the 3% hypertonic saline infusion test. The median duration of the water deprivation test in patients was 11 hours, and median duration of 3% hypertonic saline infusion test was 1.5 hour (P<0.001). CONCLUSION : The 3% hypertonic saline infusion test has a high overall diagnostic accuracy 98%; 95% CI 92% to 100%)) in relation to the classical set of clinical, laboratory and instrumental data of patients (including a water deprivation test), However, it is important the advantage of the latter is its short duration and, as a consequence, better tolerability and probably better compliance, while no significant differences in adverse events frequencies during the tests were identified.