Question 6.3



Normal Range


149 mmol/L*

135 – 145


4.5 mmol/L

3.2 – 4.5


109 mmol/L

100 – 110


24 mmol/L

22 – 33


22.0 mmol/L*

3.0 – 8.0


0.14 mmol/L*

0.07 – 0.12

Total Calcium

2.3 mmol/L

2.15 – 2.6


1.4 mmol/L

0.7 – 1.4


34 G/L

33 – 47


6.5 mmol/L

3.0 – 7.8

List four possible underlying reasons for the above biochemical profile


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College Answer

  • Dehydration
  • Steroid therapy or Cushings 
  • GI bleed
  • Protein catabolism 
  • Decreased muscle mass
  • Ruptured bladder


No history is given. Only naked blood results. This goes far to confirm the age-old impression of ICU as a specialty which is essentially a biochemical spectator sport.

Anyway. This patient has a high urea and high creatinine, with a mildly elevated potassium (though still within the normal range) and hypernatremia.

The most apparent problem is the uraemia, and thus the candidate would be expected to produce a list of differentials for an elevated urea. This hypothesis is confirmed by the college answer. To the sensible and comprehensive list of differentials which they have offered us, I will also add a few unusual differentials.

(more differentials are listed in the chapter concerned with uraemia)

Interestingly, bladder rupture is offered as a cause of these findings; it is indeed known to be a cause of biochemical features consistent with renal failure. The urea and creatinine excreted in the urine is reabsorbed via the lining of the peritoneum, meaning that the urea "recirculates" and keeps rising. However, according to the linked article, typically a ruptured bladder gives rise to hyponatremia rather than hypernatremia.


Vanholder, Raymond, et al. "Rhabdomyolysis." Journal of the American Society of Nephrology 11.8 (2000): 1553-1561.

Heyns, C. F., and P. D. Rimington. "Intraperitoneal rupture of the bladder causing the biochemical features of renal failure." British journal of urology 60.3 (1987): 217-222.

Pumphrey, C. W., and E. R. Beck. "Raised blood urea concentration indicates considerable blood loss in acute upper gastrointestinal haemorrhage." British medical journal 280.6213 (1980): 527.

WISE, BURTON L. "Hyperosmolarity (hypernatremia) and azotemia induced by the administration of urea." AMA Archives of Neurology 2.2 (1960): 160-162.

Pierrakos, Charalampos, et al. "Urea for treatment of acute SIADH in patients with subarachnoid hemorrhage: a single-center experience." Annals of intensive care 2.1 (2012): 1-7.

Yilmaz, K., et al. "Evaluation of laboratory tests in dehydrated children with acute gastroenteritis." Journal of paediatrics and child health 38.3 (2002): 226-228.

Adrogué, Horacio J., and Nicolaos E. Madias. "Hypernatremia." New England Journal of Medicine 342.20 (2000): 1493-1499.

SHILS, MAURICE E. "Renal disease and the metabolic effects of tetracycline."Annals of internal medicine 58.3 (1963): 389-408.

Thomas, David R., et al. "Understanding clinical dehydration and its treatment."Journal of the American Medical Directors Association 9.5 (2008): 292-301.

Walser, Mackenzie, and Leonard J. Bodenlos. "Urea metabolism in man."Journal of Clinical Investigation 38.9 (1959): 1617.

Simmons, Patricia S., et al. "Increased proteolysis. An effect of increases in plasma cortisol within the physiologic range." Journal of Clinical Investigation73.2 (1984): 412.