PassFinals
Endocrinology & Metabolic

Diabetes Insipidus (Arginine Vasopressin Disorder)

Diabetes insipidus is the passage of excessive dilute urine because arginine vasopressin is deficient (AVP-D, formerly cranial DI) or the kidney is resistant to it (AVP-R, formerly nephrogenic DI); the immediate danger is hypernatraemic dehydration when thirst, water access or desmopressin fails.

In a nutshell

Diabetes insipidus is excessive dilute urine from AVP deficiency (AVP-D, formerly cranial DI) or renal AVP resistance (AVP-R, formerly nephrogenic DI). Thirst and water access may keep sodium normal, but an unable-to-drink patient can develop life-threatening hypernatraemic dehydration. Desmopressin treats AVP-D, not usually AVP-R.

Classic presentation

After pituitary surgery, a patient passes large volumes of pale urine, is intensely thirsty and develops rising sodium when water or desmopressin is unavailable.

Key points

  • AVP-D is hormone deficiency; AVP-R is renal resistance.
  • Polyuria with inappropriately dilute urine and normal/high sodium is the core pattern.
  • Exclude diabetes mellitus, diuretics and primary polydipsia before specialist dynamic testing.
  • Desmopressin concentrates urine in AVP-D but not usually AVP-R.
  • Never omit essential desmopressin in a dependent inpatient; monitor sodium and fluid balance.
  • Too much desmopressin or fluid can cause dilutional hyponatraemia.

First-line investigation

Document urine output and paired serum/urine osmolality, sodium, glucose, calcium, potassium and renal function; arrange specialist dynamic testing if needed.

Management

Resuscitate decompensation

  • Treat hypernatraemic dehydration, hypovolaemia or altered consciousness as an endocrine emergency with senior endocrine/critical-care input and frequent sodium review.3,4

Protect water and medication access

  • Identify AVP-D on admission, allow safe drinking where possible and ensure the agreed desmopressin plan is not omitted or delayed.4,5

Replace deficient AVP

  • Use endocrinology-directed desmopressin for AVP-D, with current BNF/local protocol checks for formulation and dose.3,8

Avoid sodium complications

  • Balance desmopressin and fluid intake to avoid dilutional hyponatraemia, while never imposing unsupervised fluid restriction in a patient losing free water.6,2

Treat AVP resistance and cause

  • Review lithium and other causes, correct calcium/potassium/renal problems and use specialist-directed diet, thiazide or selected NSAID treatment for AVP-R.6,8

Provide endocrine safety-netting

  • Continue endocrine follow-up for sodium, renal function, other pituitary axes, cause-directed imaging and a visible emergency medication plan.3,2,7

Exam traps

  • Do not confuse diabetes insipidus with diabetes mellitus.
  • Primary polydipsia can also produce dilute urine; do not perform water deprivation outside specialist supervision.
  • A thiazide can reduce urine output in AVP-R.
  • A patient who cannot drink is more dangerous than one with intact thirst and water access.
  • Hyponatraemia, headache, nausea, confusion or weight gain on desmopressin suggests water retention, not undertreatment.

Key sources

  1. NHS: diabetes insipidus overview (NHS information on AVP physiology, AVP-D/AVP-R causes, symptoms, treatment and dehydration; page last reviewed 13 October 2022 and accessed 4 August 2026.)Updated 13 Oct 2022
  2. The Pituitary Foundation: AVP deficiency (diabetes insipidus) (UK pituitary information on AVP-D/AVP-R physiology, symptoms, diagnosis, desmopressin use, breakthrough, hyponatraemia and patient safety; accessed 4 August 2026.)
  3. Society for Endocrinology: Arginine Vasopressin Deficiency (Diabetes Insipidus) information (Current UK Society for Endocrinology clinical information covering AVP-D/AVP-R terminology, inpatient risk, fluid replacement, desmopressin and sodium monitoring; accessed 4 August 2026.)
  4. Society for Endocrinology: inpatient management of cranial diabetes insipidus (UK clinical guidance for identifying inpatients with AVP-D, ensuring access to desmopressin and water, monitoring sodium and managing decompensated disease; published 2018 and accessed 4 August 2026.)Updated 8 May 2018
  5. NHS England patient safety alert: omitted or delayed desmopressin (UK patient safety alert on severe harm or death caused by omitted or delayed desmopressin in patients with cranial diabetes insipidus; published 2016 and accessed 4 August 2026.)Updated 1 Feb 2016
  6. NHS: diabetes insipidus treatment (NHS information on desmopressin, fluid safety, hyponatraemia, lithium-related AVP-R and specialist thiazide/NSAID treatment; page last reviewed 13 October 2022 and accessed 4 August 2026.)Updated 13 Oct 2022
  7. NHS: diabetes insipidus diagnosis (NHS information on excluding diabetes mellitus, supervised water deprivation, vasopressin response, blood/urine tests and MRI; page last reviewed 13 October 2022 and accessed 4 August 2026.)Updated 13 Oct 2022
  8. British National Formulary (BNF) (Current UK prescribing information for desmopressin, thiazide diuretics and NSAIDs; product-specific formulation, dose, contraindication and monitoring details must be checked at the point of care; accessed 4 August 2026.)

This page is exam revision material, not medical advice, and must not be used for patient care. Always check drug doses against the BNF and current guidance. Full disclaimer.