Blood creatinine levels cannot be used to determine the glomerular filtration rate with complete accuracy because they are not a fully reliable measure of the glomerular blood flow rate, explains Mayo Clinic. For this reason, glomerular filtration results obtained through assessment of blood creatinine levels should be interpreted with caution.
Creatinine levels are assessed in order to determine kidney health, states Mayo Clinic. The compound is metabolized by muscles from creatine phosphate and creatine, filtered from the blood by a network of renal capillaries known as glomeruli, and eventually excreted through urine. Apart from muscular sources, a small amount of urinary creatinine originates from kidney tubules, and this causes inaccuracies of 10 percent to 20 percent when estimating the glomerular filtration rate.
The Modification of Diet in Renal Disease Study equation accurately establishes the glomerular filtration rate from blood creatinine levels, states Mayo Clinic. The equation is particularly reliable for African American and Caucasian adults of between 18 years and 70 years of age with dysfunctional kidneys.
However, when used on adults with unimpaired kidney function, this equation gives inaccurate results, warns Mayo Clinic. For this and other reasons, this method is not recommended for estimating the glomerular filtration rate of pregnant women, patients who are not between the ages of 18 years and 70 years, patients with additional disorders, and patients with muscular or nutritional extremes.