Endocrine Abstracts

Background: Arginine Vasopressin (AVP) measurement is difficult. When available there has historically been a lengthy interval between sampling and a result. Co-peptin is a 39 amino-acid glycopeptide that is derived from a pre-prohormone consisting of AVP, neurophysin II and co-peptin. It is released in an equimolar ratio with AVP into the circulation. Co-peptin is stable and can be used as a surrogate marker of AVP release in hyper and hypo-osmolar disorders. Many laboratories now measure copeptin because it is a useful marker of cardiovascular disease. The result is frequently available within a matter of hours. Levels are usually in the range 1 to 12 pmol/l and may be > 20 pmol/l in nephrogenic diabetes insipidus. We report two cases where the measurement of co-peptin levels provided the clinician with prompt, diagnostic feedback.

Case reports: Case 1: An 8 years old child with epilepsy, developmental delay and a ventriculo-peritoneal (VP) shunt for hydrocephalus secondary to neonatal meningitis presented with status epilepticus. A cranial CT scan did not demonstrate new pathology and full septic screen revealed streptococcus pneumonia meningitis. A revision of the VP shunt was performed and he was treated with antibiotics for 6 weeks. During the admission he developed hyponatraemia but was not clinically hypovolaemic. Hyponatraemia became more severe with intravenous fluid therapy including normal saline. Thyroid function and early morning cortisol level were normal and renin activity was suppressed. The syndrome of inappropriate secretion of antidiuretic hormone (SIADH) was suspected and confirmed by an inappropriately measurable co-peptin at the time of hyponatraemia.

Case 2: A 22 month old girl presented with a urinary infection and sepsis. She required fluid resuscitation and diabetes insipidus was considered because of initial hypernatraemia. Further investigations demonstrated an elevated serum co-peptin of 24.9 pmol/l when serum sodium was 150 mmol/l which ruled out cranial diabetes insipidus (CDI).

Conclusion: We have shown that copeptin can be used as surrogate marker of AVP release and can facilitate the diagnosis or exclusion of disorders such as CDI and SIADH.