Copeptin is a stable AVP marker and stoichiometrically released with AVP. It closely reflects changes in water balance. Its stimulation in severe stress has recently has been suggested in various pathophysiological conditions including myocardial infarction and stroke. Paraneoplastic stimulation of AVP/copeptin is expected in patients with cancer leading to hyponatraemia due to SIADH.
Here, we evaluated copeptin levels in 50 patients with hyponatraemia due to various forms of cancer to assess the likelihood of SIADH. Only patients with hyponatremia of <128 mmol/l were selected for the study. Copeptin levels were sampled in parallel to serum sodium levels and osmolality. Serum copeptin was measured with a specific immunoassay (detection limit of 1.7 pmol/l; maximal inter- and the intraassay CV 6.5%).
As compared to a control group and to the physiological variation found in a 24 h pattern of copeptin obtained in healthy subjects by sampling every 20 min, 20 patients exceeded the maximal range of copeptin obtained in these healthy controls by more than double of the S.D. (mean 130 vs 14 pmol/l). Copeptin levels in the remaining group of patients was not significantly different to the control group.
Our data support the idea that measurement of copeptin serum levels may provide a rapid and reliable means to distinguish patients with hyponatremia of cancer as compared to other forms of hyponatremia in the setting of cancer therapy. These determinations may guide the decision for treatment with blockers of the AVP receptor.