A 54 year old lady, seeing her Family Doctor. Clinical information is 'Type
2 diabetes mellitus'.


Serum creatinine:	46 umol/L
24 hour urine volume:	1760 ml
Urine creatinine:		9270 umol/L
Clearance:		242 ml/ min
Urine protein:		0.17 g/L

This Case attracted 36 participants, including new ones from France and
Australia - welcome! The participants fell into 3 neat groups, those
querying the serum creatinine; those querying the urine creatinine; and
those querying pathological causes for the high creatinine clearance. One
assessor commented that this was difficult to score, and there were some
marked differences of opinion between the assessors, indicated by the
asterisks below.

8 participants would check the serum and urine creatinines before
reporting; [1.8]

2 participants said impossible/ unphysiological clearance; [0*]
10 said unusually high clearance [0.5*]
	5 queried analytical interferences; [0*]
	4 suggested correcting it for body weight/ height; [-0.3]
	2 queried a low body surface area; [-0.3]
	2 queried hyperfiltration; [0.7]
	1 said this may indicate poor diabetic control; [0.8]
	1 queried hyperosmolar diuresis [-0.8]

4 commented that the serum creatinine was low; [1.3]
	2 queried analytical interference; [0.5*]
	2 suggested low body weight or low muscle bulk; [1.5]

2 participants said the urine creatinine output was high; [1.0]
8 queried the correct or more than 24 hour urine sample; [1.8]
2 queried ketone interference; [1.0]
1 queried glycosuria. [-0.5]

11 participants commented on the raised protein excretion; [2.0]
10 suggested checking the albumin excretion rate; [0.3*]
4 suggested checking the state of diabetic control; [-0.3*]
2 advised checking blood pressure; [-1.8]
1 suggested excluding infection and considering renal ultrasound. [-0.3]
1 suggested urine protein electrophoresis. [-0.5]

10 participants said that results suggested the early phase of diabetic
renal disease. [0]

10 participants would suggest repeating the creatinine clearance; [1.3]
5 queried if the clearance was necessary; [1.3]

2 suggested referral to a Diabetologist. [0.5]

I have considerable confidence in our own enzymic creatinine method, which
is subject to few interferences. Previous results on this patient had not
included a urine creatinine, but showed a steady decrease in serum
creatinine from 61 umol/L a year before. A microalbumin/ creatinine ratio 3
months before was less than 0.3 (ie within reference limits).
To me, the low serum creatinine implied a small muscle mass, and with this,
the total urine creatinine output seemed considerably higher than expected.
And although I believe that gfr can increase slightly in the early phase of
diabetic renal disease, this clearance seemed far too high. If this urine
collection was around 48 rather than 24 hours, the proteinuria is very
slight.My comment was therefore
'Very high clearance, and urine creatinine output much higher than
expected. Considerably more than a 24 hour collection? Slight proteinuria -
worth re-checking albumin/creatinine ratio?'
I do not know why creatinine clearance was requested on this patient - I
guess because trace proteinuria was detected by dipstick at a clinic visit,
the Family Doctor thought it was worth checking a 24 hour urine protein
output; and since he was obtaining a 24 hour urine sample anyway, added
clearance on as an easy extra test. 'Routine' diabetic monitoring round
Reading does not include creatinine clearance, but does include occasional
random samples for microalbumin/ creatinine.

Best wishes
Gordon Challand


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