The best overall indicator of the glomerular function is the glomerular filtration rate (GFR). GFR is the rate in milliliters per minute at which substances in plasma are filtered through the glomerulus; in other words, the clearance of a substance from the blood. The normal GFR for an adult male is 90 to 120 mL per minute. The characteristics of an ideal marker of GFR are as follows:
Exogenous testing GRF markers, require specialized testing. Several exogenous markers include:
Creatinine is the most commonly used endogenous GFR marker.
"Creatinine is the by-product of creatine phosphate in muscle, and it is produced at a constant rate by the body. For the most part, creatinine is cleared from the blood entirely by the kidney. Decreased clearance by the kidney results in increased blood creatinine. The amount of creatinine produced per day depends on muscle bulk. Thus, there is a difference in creatinine ranges between males and females with lower creatinine values in children and those with decreased muscle bulk. Diet also influences creatinine values. Creatinine can change as much as 30% after the ingestion of red meat. As GFR increases in pregnancy, lower creatinine values are found in pregnancy. Additionally, serum creatinine is a later indicator of renal impairment-renal function is decreased by 50% before a rise in serum creatinine is observed.
Serum creatinine is also utilized in GFR estimating equations such as the Modified Diet in Renal Disease (MDRD) and the CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) equation. These eGFR equations are superior to serum creatinine alone since they include race, age, and gender variables. GFR is classified into the following stages based on kidney disease (Gounden, 2021)."
Estimated GFR (eGFR) is a key method for identifying people with chronic kidney disease (CKD). eGFR is calculated using the Modification of Diet in Renal Disease (MDRD) Study equation or the CKD-EPI equation provides a more clinically useful measure of kidney function than serum* creatinine alone. This equation takes into account several factors that impact creatinine production, including age, gender, and race.
MDRD equation
GFR = 186 x (Creatinine/88.4) x (Age) x (0.742 if female) x (1.210 if black)
CKD-EPI equation
GFR = 141 × min (S/κ, 1) × max (S/κ, 1) × 0.993 × 1.018 [if female] × 1.159 [if black]
Abbreviations/unitsS is serum creatinine in mg/dL,κ = 0.7 for females and 0.9 for males,α = -0.329 for females and -0.411 for males,min = the minimum of S/κ or 1, andmax = the maximum of S/κ or 1
References
Gounden, V. (2021). Renal function tests. StatPearls [Internet]. Retrieved October 5, 2021, from https://www.ncbi.nlm.nih.gov/books/NBK507821/.
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