Endocrine Abstracts

Background: The diagnosis of central diabetes insipidus (DI) relies on indirect measurement of serum/urine sodium and osmolality. Since the diagnosis can only be made when an inappropriately dilute urine is paired with a significantly concentrated serum, the process is tedious for the clinician and uncomfortable for the patient. Copeptin is the C-terminal portion of the anti-diuretic hormone (ADH) prohormone which correlates with the less stable ADH, therefore providing a direct measurement of posterior pituitary response to hyperosmolar stress^1,2.

Aim: This study aims to assess the diagnostic accuracy of copeptin in patients with central DI compared with subjects who underwent pituitary surgery without DI.

Methods: Serum samples from subjects with central DI, control subjects post pituitary surgery with no DI (NDI) and control subjects with SIADH were collected and analysed on the BRAHMS KRYPTOR copeptin assay. Groups were compared using unpaired T-test and Levene’s test for equal variance.

Results: 56 samples from 22 subjects (13 females, nine males, mean age 53.9 ± 15.5 y.o.) were analysed. Two subjects had resolved DI (RDI) after copeptin analysis and were successfully weaned off DDAVP and reclassified as NDI. Of the DI subjects, 1 had acute and 5 had chronic DI. Copeptin was lower in DI compared to NDI group (P = 0.013), while serum sodium, osmolality, urine osmolality were similar. Copeptin did not differentiate between the SIADH and NDI groups. After exclusion of NDI samples with serum sodium ≤ 140 mmol/l, the area under the curve was 0.97 (95% CI 0.9 to 1.0), a copeptin cut-off of 2.9 pmol/l predicts DI with a sensitivity of 92% and a specificity of 90%.

Conclusion: Copeptin concentration of < 3.0 pmol/l concurrently with serum sodium concentration of > 140 mmol/l predicted central DI when using post pituitary surgery subjects without DI as controls.

References

1. Winzeler, B et al. JCEM 2015.

2. Fenske, W et al. NEJM 2018.