Na+

149

135-145 mmol/L

K+

4.5

3.5-5.0 mmol/L

Cl-

109

100-109 mmol/L

HCO3-

24

22-33 mmol/L

Urea

40

2.7-8.0 mmol/L

Creatinine

140

50-120 micromol/L

Ca++

2.3

2.1-2.6 mmol/L

PO4-

1.4

0.8-1.45 mmol/L

Albumin

34

33-50 mmol/L

Gluc

6.5

3.0-7.8 mmol/L

A) List 3 differential diagnoses of the above plasma  biochemistry ?

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College Answer

A)        Dehydration
B)        GIT bleed
C)        Steroid therapy

Discussion

This question is almost identical to Question 6.3 from the second paper of 2012. In this version, the college increased the urea to 40mmol/L, and asked for only three differentials.  Differentials listed in the chapter concerned with uraemia are reproduced below to simplify revision.

Causes of a Raised Urea

Increased exogenous urea

  • Urea administration (eg. for management of SIADH)

Decreased urea clearance

Increased renal reabsorption of urea

  • States of apparent hypovolemia (eg. CCF, renal artery stenosis)
  • Actual hypovolemia (i.e. dehydration)

Decreased renal clearance of urea

  • Decreased glomerular filtration rate (eg. renal failure)
  • Decreased active tubular secretion (corticosteroids)

Increased urea synthesis

Increased protein intake

  • High protein diet
  • Gastrointestinal haemorrhage
  • Parenteral oversupplementation of amino acids (TPN)

Increased protein catabolism

  • Corticosteroids
  • Trauma
  • Burns
  • Major surgery
  • Starvation (acute)