July 30, 2016 : Creatinine Clearance (Cockcroft-Gault) for the Medical Calculator
© 安岡喜晴 (JoyShine)
I added Creatinine Clearance (Cockcroft-Gault) functions to the
Medical Calculator.
Creatinine clearance is estimated with the Cockcroft-Gault equation.
Age, weight, and serum creatinine, then multiply by 0.85 for women.
That 0.85 comes from the fact that women carry less muscle.
Serum creatinine comes from muscle, so at the same weight a woman produces less of it.
Without that correction, the equation puts her clearance higher than it really is.
But that figure was not derived from female data.
When the equation was published in 1976, it was built on 249 patients, and every one of them was a man.
The 0.85 was added afterwards without measuring anything, it was just an estimate.
Even now, that estimate is still deciding how much drug a woman gets.
static const CalcInput CRCL_CG_INPUTS[] = {
{ L"Age (years)", INPUT_NUMBER, NULL },
{ L"Weight (kilograms)", INPUT_NUMBER, NULL },
{ L"Serum Creatinine (mg/dL)", INPUT_NUMBER, NULL },
{ L"Sex", INPUT_CHOICE, L"Male|Female" },
};
inline void calc_crcl_cockcroft_gault(const double* in,
wchar_t* disp, size_t dsz,
wchar_t* pri, size_t psz,
wchar_t* det, size_t esz) {
double age = in[0], w = in[1], scr = in[2];
bool female;
if (!val_age_adult(age) || !val_pos(w) || !val_pos(scr) ||
!val_bool01(in[3], &female)) {
calc_err(disp, dsz, pri, psz, det, esz,
L"Cockcroft-Gault is for adults (age 18-120). Age, weight, creatinine must be > 0. For pediatric estimation use Schwartz/CKiD-U25.");
return;
}
double crcl = ((140 - age) * w) / (72 * scr);
if (female) crcl *= 0.85;
wchar_t b[32];
fmt_g(b, 32, crcl);
swprintf(disp, dsz, L"%ls", b);
swprintf(pri, psz,
L"CrCl (Cockcroft-Gault) : %ls mL/min\r\n"
L"Drug-dosing band : %ls\r\n"
L"Uses actual body weight: in obesity this overestimates CrCl and in low body weight underestimates it; consider ideal / adjusted body weight per drug labeling.\r\n"
L"Note: CrCl in mL/min (not BSA-normalized). Do NOT interpret directly as a KDIGO CKD G-stage (which uses GFR mL/min/1.73 m^2 + albuminuria).",
b, crcl_dosing_band(crcl));
(void)esz; det[0] = 0;
}