Copeptin

Where it comes from

Made in

The same neurons as vasopressin, one copeptin for every vasopressin

Sent out by

Exactly with vasopressin: thirst, low volume, stress

Acts on

• None

What it does

• Helps pro-vasopressin fold in the neuron
• Lasts in blood where vasopressin lasts minutes and sticks to platelets
• A mirror of vasopressin release

In medicine

• The modern test for diabetes insipidus: copeptin after hypertonic saline tells vasopressin deficiency from primary polydipsia better than the water deprivation test; copeptin after arginine is simpler but less accurate ¹
• A low copeptin with a normal troponin at presentation lets a heart attack be ruled out early in people at low risk, which matters most for those who arrive before troponin has had time to rise ³
• A stress marker that predicts outcome in pneumonia, stroke and sepsis ⁴

Beyond the body’s own use

• What it settles: with a cutoff of 4.9 pmol/L after hypertonic saline, copeptin reached the right diagnosis in 96.5 per cent of 141 patients with hypotonic polyuria, against 76.6 per cent for the water deprivation test ¹
• What it demands: that test works by raising plasma sodium and needs close monitoring, and the simpler arginine-stimulated version was less accurate, 93 per cent in the pooled cohorts ²
• What it cannot do alone: a single copeptin does not exclude a heart attack. Paired with a troponin in 902 patients it allowed safe early discharge of low-risk cases, with a 0.6 per cent event rate among those sent home ³
• What it will not tell you: as a stress marker it tracks how ill someone is and points to no particular cause, so a raised level in pneumonia, stroke or sepsis carries prognosis and not diagnosis ⁴