A number of threads about creatinine clearance have been running since
April this year, the most recent about correction for body surface
area. I believe creatinine clearance to be a redundant clinical
investigation (Ann Clin Biochem 1986; 23: 243). Here are some data that
illustrate why.
The gold standard for GFR is inulin clearance. Inulin, dextran and DTPA
clearances agree closely. Even under carefully controlled experimental
(not clinical) conditions, creatinine clearance is higher and diverges
widely:
Inulin clearance(ml/min) Creatinine clearance(ml/min)
20 20 - 65
40 50 - 80
60 65 - 90
80 85 - 110
90 100 - 165
(Data from Shemesh et al. Kidney Int 1985; 28: 830).
Plasma concentration should be constant during the measurement of any
endogenous clearance. Plasma creatinine increases after a meat meal
rising, for example, in six normals from a mean of 90 umol/L to 175
umol/L three hours after a goulash containing 250 - 300 g of beef (data
from Jacobsen et al, Lancet 1980; i: 319). An increased urine excretion
rate of course follows.
Shemesh et al make the sensible suggestion that in renal patients true
GFR should be determined occasionally using DTPA and that changes in GFR
should be routinely monitored by the measurement of plasma creatinine
(the blood sample being taken either fasting or after a meat free
meal). In this way the relationship between true GFR and plasma
creatinine is determined for the individual patient whatever his or her
age, height or weight, rather than being calculated using algorithms
derived from population measurements.
Should we not try to persuade our clinical colleagues to adopt this
approach?
Brian Payne
(PS: my address is now [log in to unmask])
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