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DOI: 10.1055/s-0034-1372046
Copeptin in the Diagnosis and Differential Diagnosis of Diabetes Insipidus – The ‘CoSIP-Study’
The correct differential diagnosis of the disorders related to polyuria-polydipsia syndrome (PPS) is mandatory since inadequate treatment may lead to serious complications. The diagnostic gold standard is the water deprivation test (WDT) with direct or indirect measurement of plasma vasopressin (AVP). But test interpretation is problematic, and direct measurement of AVP is hampered by methodological difficulties. The aim of this study was to evaluate the diagnostic accuracy of copeptin in the differential diagnosis of DI.
In a prospective multicenter study, patients with a history of PPS and indication for a WDT were consecutively included. The WDT started at 8 am with a baseline blood and urine sampling and was terminated once S-Na+ levels increased > 147mmol/L. If this cutoff was not reached by fluid deprivation alone, a 3% saline infusion was administered. Serum samples were obtained hourly for measurement of copeptin and AVP.
We present results of the first 52 patients with full data available: 13 with complete, 12 with partial central DI, 17 with PP, and 10 with nephrogenic DI. 29 were women, 23 were men. Mean (SD) age was 45 (16)yrs. Baseline copeptin levels ranged from 21 – 117 pmol/L in patients with nephrogenic DI, from 0.7 – 5.1 pmol/L in patients with central DI (complete: 0.7 – 4.1 pmol/L; partial: 0.8 – 5.1 pmol/L) and from 0.9 – 13.5 pmol/L in patients with primary polydipsia. Without prior thirsting, a single baseline copeptin level of > 20 pmol/L perfectly differentiated nephrogenic DI from all other etiologies with a sensitivity and specificity of 100%, rendering a WDT unnecessary. Furthermore, a delta copeptin increase under osmotic stimulation of < 2 pmol/L differentiated patients with central DI from patients with primary polydipsia with a specificity of 95.8%, a sensitivity of 94.1% and a positive likelihood ratio of 22.6.
Copeptin is a promising new tool in the complex diagnosis of polyuria-polydipsia syndrome.