SAN FRANCISCO – Measuring plasma copeptin levels may provide an accurate and easier way to identify the cause of severe hyponatremia, compared with measuring arginine vasopressin levels, preliminary data on 175 patients suggested.
A plasma copeptin level greater than 70 pmol/L correlated with a diagnosis of hypovolemic or diuretic-induced hyponatremia requiring saline infusion with 91% specificity. A copeptin/urinary sodium ratio greater than 1.84 identified patients who clearly needed saline infusion with a specificity of 90%, Dr. Nicole Nigro reported at the annual meeting of the Endocrine Society.
"The differential diagnosis of hyponatremia is not easy to make" and often relies on detecting adequate or inadequate plasma levels of arginine vasopressin (AVP), she said in an interview. Blood samples for AVP measurements must be kept on ice, making handling and transportation to the lab more difficult. AVP mostly attaches to platelets, it clears rapidly, and AVP levels are known to be very unstable.
Dr. Nicole Nigro
Copeptin, on the other hand, is very stable in plasma, easy to measure, and released by the body in an equimolar ratio with AVP, said Dr. Nigro of University Hospital, Basel, Switzerland.
She presented data on the first 175 patients in an ongoing study that has enrolled 290 of an expected 300 consecutive patients who present with severe hypo-osmolar hyponatremia at the emergency departments of two Swiss tertiary referral centers. All patients had a sodium level below 125 mmol/L. Three experts who were blinded to patients’ copeptin levels made the final diagnoses based on a clinical algorithm, a chart review, and response to therapy.
The median plasma copeptin level was 2.8 pmol/L in 17 patients diagnosed with primary polydipsia, 13.2 pmol/L in 45 patients with diuretic-induced hyponatremia, 13 pmol/L in 56 patients with syndrome of inappropriate antidiuretic hormone, 28 pmol/L in 25 patients with hypervolemic hyponatremia, and 55 pmol/L in 32 patients with hypovolemic hyponatremia, Dr. Nigro reported in an oral presentation and a featured poster at the meeting.
The 77 patients who required saline infusion had significantly higher copeptin levels (27 pmol/L), than patients who did not need saline (12 pmol/L).
Dr. Nigro’s hospital routinely measures copeptin levels but is not yet using them to guide the differential diagnosis of hyponatremia. If the current study produces clear findings when it’s finished, the investigators next may conduct a study that uses copeptin levels to guide treatment of patients with severe hyponatremia.
Ultimately, "copeptin may help us to guide the therapy and management of these patients with severe hyponatremia," she suggested.
Some of Dr. Nigro’s associates in the study have been speakers for B.R.A.H.M.S./Thermo Fisher Scientific. She reported having no other relevant financial disclosures.
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