Creatinine is a byproduct of creatine phosphate in muscles. The creatinine is released into the blood stream, but is not reabsorbed by the body. The kidneys subsequently filter the creatinine out of the blood. By measuring creatinine levels in the blood and urine, you can estimate the creatinine clearance, which gives a reasonable estimate of kidney function, or the glomerular filtration rate. The values of the GFR or the creatinine clearance could indicate healthy or distressed kidneys. If 24-hour urine and blood analysis are not available, the creatinine clearance can be estimated using the level of creatinine level in the blood.
Calculate the base creatinine clearance by considering weight, age and plasma creatinine levels of the patient. The formula is:
Base Creatinine Clearance = [[1.2 * (140 - Age(yrs)) * Weight(kg)] / Plasma Creatinine(µmoles/L)]
As an example, your patient is 40 years old, weighs 70 kg with a Plasma Creatinine level of 85 micromoles/liter:
Creatinine Clearance = [[1.2 * (140 - 40) *70] / 85]
Creatinine Clearance = 98.8
Multiply the base creatinine clearance by any adjustment values:
Women: Multiply by 0.85
Black ethnicity: Multiply by 1.18
If the example patient is a female, the creatinine clearance is:
Creatinine Clearance = Base Creatinine Clearance * Adjustment
Creatinine Clearance = 98.8 * 0.85
Creatinine Clearance = 84.0
If the patient is a white male, the adjustment is just 1.0, so the creatinine clearance would equal the base amount calculated earlier.
Compare creatinine levels to determine kidney function:
40-75: Kidney function some what reduced, although patient will be asymptomatic.
15-40: Kidney function reduced and requires further tests
under 15: Kidney function critically low and patient needs to see a kidney specialist.
In the example, your patient's creatinine clearance was 84.0, which falls within the normal range.