Question 20.1

The following venous blood results are from a 56-year-old patient presenting with abdominal pain.

Parameter	Patient Value	Adult Normal Range
Sodium	130 mmol/L*	135 – 145
Potassium	5.1 mmol/L*	3.5 – 5.0
Chloride	101 mmol/L	95 – 105
Bicarbonate	10 mmol/L*	22 – 28
Creatinine	305 mmol/L*	50 – 100
Urea	75.6 mmol/L*	3.5 – 7.2
Glucose	5.2 mmol/L	3.5 – 6.0
Calcium corrected	2.05 mmol/L*	2.12 – 2.62
Ionized Calcium	0.97 mmol/L*	1.14 – 1.30
Phosphate	3.97 mmol/L*	0.73 – 1.37
Protein	66 g/L	61 – 83
Albumin	29 g/L*	35 – 50
Alkaline phosphatase	220 U/L*	30 – 110
g-Glutamyl transferase	30 U/L	< 40
Alanine transferase	27 U/L	< 35
Magnesium	0.83 mmol/L	0.75 – 0.95

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College answer

Not available.

Discussion

That's not a lot of history, and therefore for the candidates the real struggle would have been to fight the natural urge to spend a few minutes connecting these abnormalities into a single grand unifying diagnosis. Fortunately, one immediately presents itself.

So: the abnormalities are:

Hyponatremia: which is only very mild
Hyperkalemia: which is again only mild
Metabolic acidosis which appears to be mainly NAGMA:
the anion gap is slightly raised (19), and therefore the delta ratio is 0.5
Creatinine is rather elevated
Urea is wildly elevated, much more than the rise in creatinine
Calcium is low, including both the total and ionised
Phosphate is raised
Albumin is low, which is incredibly non-specific
Of the LFTs, only the alk phos is raised.

What could have caused all this, AND abdominal pain? The mind boggles. However, even the boggling mind would agree that the urea of 76 (!) is the most profoundly disturbed value here. Renal failure is also present, and any kind of renal failure could be to blame for the creatinine rise, but only one kind of renal failure can give rise to a urea/creatinine ratio so heavily skewed in favour of urea. The abdominal pain here, therefore, must clearly be the pain of a humongously overdistended (if not ruptured) bladder. This is obstructive uropathy. Marshall (1964) explained this phenomenon as the result of increased hydrostatic pressure in the tubule which slows tubular transport and increases the transport of urea out of the tubule lumen.

Thus:

Raised urea and creatinine due to obstructive uropathy
Metabolic acidosis and raised phosphate due to renal failure
Depressed calcium due to raised phosphate
Elevated alk. phos. due to hypocalcemia-induced PTH release
Hyponatremia due to inadequate water excretion
Hyperkalemia due to renal failure and acidosis

References

Marshall, Sumner. "Urea-creatinine ratio in obstructive uropathy and renal hypertension." JAMA 190.8 (1964): 719-720.

Zamzami, Zuhirman. "Blood urea and creatinine levels in obstructive uropathy patients due to benign prostate hyperplasia after transurethral resection of the prostate." International Journal of Surgery and Medicine 5.1 (2019): 18-22.

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