Question 5.2

A 47-year-old, previously well, 70 kg male was admitted to the Emergency Department with agitation and confusion. Following catheterisation, his urine output in the next few hours was 300 — 350 ml/hr. The results of his blood tests are as follows:


Patient Value

Adult Normal Range


169 mmol/L*

135 - 145


4.6 mmol/L

105 mmol/L


95 - 105


26.0 mmol/L

22.0 - 26.0


6.6 mmoI/L*


9.6 mmol/L*  


115 prnoI/L*

45 — 90


0.88 mmol/L

0.75 - 0.95


28 g/L*

35 - 50


58 g/L*

60 - 80

Plasma osmolality

360 mmol/kg*

290 - 310

Urine specific gravity


1 .010 - 1.030

a) What is the most likely diagnosis?           (10% marks)

b) How would you manage the hypernatremia?        (30% marks)

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College answer


Diabetes Insipidus


  • Examination to assess fluid status, Cardiac status 
  • Specific therapy -  o 5%Dextrose or Sterile water administration with hourly Sodium Measurement- calculate water deficit and correct over time frame
    • Stop offending medications. If history of Lithium Intake-Lithium Levels 
    • Desmopressin or vasopressin 
    • Thiazides/Amiloride/Acetazolamide (if lithium)
    • Avoid rapid correction

Examiner Comments:

Management of diabetes insipidus was handled poorly, as some of the described fluid regimes were considered dangerous


The major abnormalities are:

  • Hypernatremia
  • Hyperosmolarity with no osmolar gap 
  • Low albumin
  • Near maximally dilute urine

This is clearly diabetes insipidus. The urine findings and and the low osmolar gap rule out the interference of things like mannitol.

Management of diabetes insipidus consists of two major strategies:

1) Correct the water balance.

  • Calculate the water deficit:  total body water × (1- [140 ÷ serum sodium])
    In this guy's case, they gave you his weight (70kg). That gives him a total body water of 42L. Thus, he needs approximately 7.14 L of water.
  • Water should be corrrected as isotonic dextrose, but can also be given as pure water via the NG (infusion of sterile water is generally not done).

2) Interrupt the pathophysiology

  • If there is an obvious drug--related cause, stop the drugs (eg. the lithium suggested by the college. Then, either replace the ADH or stimulate its secretion:
    • Antidiuretic hormone analogues:
      • Arginine vasopressin
      • Desmopressin (DDAVP)
    • Antidiuretic hormone release stimulating drugs
      • Clofibrate
      • Clorpropamide
    • In case of nephrogenic DI:


Singer, Irwin, James R. Oster, and Lawrence M. Fishman. "The management of diabetes insipidus in adults." Archives of internal medicine 157.12 (1997): 1293-1301.

Libber, Samuel, Harold Harrison, and David Spector. "Treatment of nephrogenic diabetes insipidus with prostaglandin synthesis inhibitors." The Journal of pediatrics108.2 (1986): 305-311.

Knoers, N., and L. A. H. Monnens. "Amiloride-hydrochlorothiazide versus indomethacin-hydrochlorothiazide in the treatment of nephrogenic diabetes insipidus." The Journal of pediatrics 117.3 (1990): 499-502.