Introduction: Copeptin is a proposed new diagnostic marker in differential diagnosis of diabetes insipidus as it is secreted in equimolar concentrations with vasopressin. Thus our aim was to assess diagnostic value of copeptin evaluation in patients with polydipsic-polyuric disorders.
Materials and Methods: Weve evaluated the copeptin (BRAHMS CT-proAVP Kryptor), sodium levels and blood/urine osmolality in 26 healthy volunteers (1M/25F, mean age 24.7±2 years) water deprived for 12 h as well as in 3 patients with central diabetes insipidus (CDI) and 3 patients with primary polydipsia (PP) during water deprivation test.
Results: In 38% (10 patients) of healthy volunteers copeptin level was less than 5 pmol/l (the lower limit of laboratory). The remaining average levels amounted to 8.5±2.8 pmol/l (5.41 to 15.16). In patients with polyuria morning concentrations of copeptin were less than 5, and only one patient who later was diagnosed as CDI were 6.124 pmol/l. After water deprivation till maximum tolerability (48 h) patients with PP concentrated urine above 650 mOsm/kg and their copeptin levels increased to 13.59, 16.56, and 11.76 respectively, serum sodium and osmolality were within normal rangers and without any significant changers from basal values. In patients with CDI the levels of copeptin for all were below 5 pmol/l, serum sodium and osmolality increased while urine osmolality remained below 300 mOsm/kg. The Index for stimulated CT-proAVP (the formula provided by assay developer) was 0 for patients with CDI and 60, 81 and 47 for patients with PP (>20 is diagnostic for PP).
Conclusions: Basal copeptin levels in our setting were not helpful for differentiation of healthy people from patients with CDI, but this differentiation was possible with water deprivation test alone with concordant information from copeptin/sodium index calculation.