Background: Polyuria and polydipsia syndrome (PPS) workup is not straightforward, especially in children. Basal investigations are often not reliable in distinguishing among diabetes insipidus (DI), central (CDI) or nephrogenic (NDI), and primary polydipsia (PP). Water deprivation test (WDT) is often essential, although uncomfortable and not always reliable enough to recognize partial DI. Plasma AVP investigation is not routinely used in the diagnostic pathway as AVP measurement is technically difficult for the hormone instability and the high in vitro thermolability. Urine AVP (U-AVP) assessment, on the contrary, is not biased by the same complications and was firstly proposed in early 2000s, but not further developed later on. We investigated U-AVP in a small group of patients with PPS and in a control group.
Methods: We retrospectively assessed AVP in urine samples of patients presenting with PPS (2M,3F), after more common causes of polyuria were excluded. Urine samples were collected as basal and during WDT, along with plasma and urine osmolality (POUO). Patients were diagnosed with CDI (1M,1F) and PP (1M,2F) on the basis of PO and UO values during WDT, according to standard reference ranges. DDAVP test was performed to discriminate NDI from CDI. Furthermore, we collected blood and urine samples for PO, UO and U-AVP in a control group (5M,8F), who had not history of PPS and with normal neuropituitary bright spot at MRI. SPSS program was used for statistical analysis. Commercial RIA kit was used for U-AVP analysis.
Results: U-AVP was measurable in all urine samples collected in control and PP group. Mean U-AVP was significant higher in controls than PP patients, 59.9 and 15.3 pmol/l respectively (P<0.5). U-AVP was directly correlated to urine osmolality both in control and PP group (P<0.01, R2=0.32). U-AVP was undetectable on basal urine samples of CDI patients. U-AVP increased during WDT in PP patients. Conversely, CDI patients did not show significant U-AVP increase to prevent PO over 300 mmOsm/kg. U-AVP increased in CDI patients during DDAVP-test.
Conclusions: We demonstrate that AVP can be directly, easily and painless assessed in urine. U-AVP seems helpful in distinguishing CDI from PP, and makes DDAVP test needless. U-AVP may play also a role in the assessment of adherence to treatment in CDI patients. Undoubtedly, larger cohorts are needed to validate the few data presented. Anyway, U-AVP analysis might be a new tool in the diagnostic pathway of the PPS and to co-adjuvate clinical decisions.
19 Sep 2019 - 21 Sep 2019