Goldwasser P, Aboul-Magd A, Maru M
Race influences creatinine production in men with renal
insufficiency
Am Soc Nephrol
J Am Soc Nephrol (abstract)
(Sep) 7:1318 1996
Cockcroft and Gault noted that the excretion of creatinine per kilogram per
24 hours (Cr24/kg) decreased with age in a linear fashion, with a
regression very closely fit by the formula:
Formula 1) Cr24/kg = 28-(age x 0.2)
Rearrangement/substitution into the formula for clearances, i.e.
Formula 2) Clcr = Ucr x Volume in 24 hours/Pcr,
leads to the more familiar Cockcroft - Gault formulation, i.e.
Formula 3) Clcr = ((140 - age) x wt kg) / (72 x Scr)
The 1976 report by Cockcroft and Gault noted several factors which could
interfere with the predictive power of their formulation: female sex,
differences in muscle mass, dietary factors, etc.(1)
The abstract by Goldwasser examined creatinine production in "black" and
"non-black" male patients. After measuring 24 hours urine creatinine
excretion, Cr24/kg was calculated. Cr24/kg was 14% higher among blacks
than non-black patients in a retrospective study of 69 patients. In
another prospective study of 28 patients Cr24/kg was 36% higher in blacks
than non-black patients. They noted that Formula 1 correlated well with,
but underestimated, measured Cr24/kg in black patients.
Comment: One confounding difference between these groups of black and
non-black patients is age; the latter were significantly older that the
former. Cockroft and Gault described the decrement in Cr24/kg with
increased age. If there is indeed an increased creatinine production per
kilogram in black male patients compared to non-black, what would be the
impact on the measurement of kidney function? Given the data in this
abstract it would follow that in a group of patients with identical renal
function, the black patients would have a higher serum creatinine and
therefore a lower Cockcroft estimate of creatinine clearance. Neither
serum creatinine levels nor other data which allow comparison of GFR are
given. Without this data it is not possible to assess the predictive value
of the Cockcroft - Gault formula per se.
(Greg Cowell, M.D., University of Illinois at Chicago)
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Am Soc Nephrol
Assessing renal function :
Creatinine clearance
H: Special problems :
Ethnic populations