Function tests

Function-tests » Letter F » Fluid deprivation test

Indication

Differential diagnosis of polydipsia/polyuria (Central diabetes insipidus, renal diabetes insipidus, habitual polydipsia).

Contraindication

Dehydration. Permanent monitoring required.

Principle

Evaluation of basal or stimulated copeptin.

Procedure

For procedure and evaluation, please refer to the flow diagram below.

Evaluation

Flow diagram fluid deprivation diabetes insipidus copeptin

Initial blood collection

Basal copeptin (mornings,

fasting after 8 hours dehydration)

Copeptin <2,6 pmol/l

Copeptin 2,6 – 20 pmol/l

Copeptin > 20 pmol/l

Second extraction of blood

Copeptin and serum sodium

(fasting after 16 hours dehydration)

Evaluation of copeptin-index:

Copeptin (8h – 16h) x 1000 (pmol/mmol/l):

Serum sodium (16h)

Copeptin-index < 20

Copeptin-index ≥ 2