creatinine clearance (CC, Estimated glomerular filtration rate [eGFR])
المؤلف:
Kathleen Deska Pagana, Timothy J. Pagana, Theresa Noel Pagana.
المصدر:
Mosbys diagnostic and laboratory test reference
الجزء والصفحة:
15th edition , p309-311
2025-12-02
130
Type of test Urine (24-hour); blood
Normal findings
Adult (< 40 years)
Male: 107-139 mL/min or 1.78-2.32 mL/s (SI units)
Female: 87-107 mL/min or 1.45-1.78 mL/s (SI units)
Newborn: 40-65 mL/min
Values decrease 6.5 mL/min/decade of life because of decline in GFR.
eGFR: > 60 mL/min/1.73 m2
Test explanation and related physiology Creatinine is a catabolic product of creatine phosphate, which is used in skeletal muscle contraction. The daily production of creatinine depends on muscle mass, which fluctuates very little. Creatinine is entirely excreted by the kidneys and therefore is directly proportional to the glomerular filtration rate (GFR; i.e., the number of milliliters filtered by all the nephrons in the kidneys per minute). The creatinine clearance (CC) is a measure of the GFR.
The CC depends on the amount of blood present to be filtered and the ability of the nephron to act as a filter. The amount of blood present for filtration is decreased in renal artery atherosclerosis, dehydration, or shock. The ability of the nephron to act as a filter is decreased by such diseases as glomerulonephritis, acute tubular necrosis, and most other primary renal diseases.
When one kidney becomes diseased, the opposite kidney, if normal, has the ability to compensate by increasing its filtration rate. Therefore with unilateral kidney disease or nephrectomy, a decrease in CC is not expected if the other kidney is normal.
Several nonrenal factors may influence CC. With each decade of age, the CC decreases 6.5 mL/min because of a decrease in the GFR. Urine collections are timed, and incomplete collections will falsely decrease CC. Muscle mass varies among people. Decreased muscle mass will give lower CC values.
The CC test requires a 24-hour urine collection and a serum creatinine level. The uncorrected CC is then computed using the following formula:
Creatinine clearance = 
where
U = Number of milligrams per deciliter of creatinine excreted in the urine over 24 hours
V = Volume of urine in milliliters per minute
P = Serum creatinine in milligrams per deciliter
The corrected CC calculation takes into account the average body surface area.
The 24-hour urine collections used to measure CC are too time-consuming and expensive for routine clinical use. The GFR can be estimated (eGFR) using the Modification of Diet in Renal Disease (MDRD) Study equation. This is an equation that uses the serum creatinine, age, and numbers that vary depending on sex and ethnicity to calculate the GFR with very good accuracy. The prediction equation for GFR is as follows, with Pcr being serum or plasma creatinine in mg/dL: The GFR is expressed in mL/min/1.73 m2.
More and more, institutions across the country are beginning to report an eGFR on patients 18 years and older with every serum creatinine ordered. The eGFR calculation can be programmed into most laboratory information systems. As a result, chronic renal disease is being recognized more frequently in its early stages. Chronic kidney disease can be treated and progression to renal failure slowed or prevented. The eGFR can also be used to calculate medication dosage in patients with decreased renal function.
Table 1 shows population estimates for mean (average) eGFR by age. There is no difference between races or sexes when eGFRs are expressed per meter squared body surface area. For diagnostic purposes, most laboratories report eGFR values above 60 as greater than 60 mL/min/1.73 m2, not as an exact number.
Table1. Mean estimated glomerular filtration rates (eGFRs)
Interfering factors
• Exercise may cause increased creatinine values.
• Incomplete urine collection may give a falsely lowered value.
• Pregnancy increases CC.
• A diet high in meat can transiently elevate CC.
• The eGFR may be inaccurate in extremes of age and in patients with obesity, severe malnutrition, paraplegia, quadriplegia, or pregnancy.
* Drugs that may cause increased levels include aminoglycosides, cimetidine, heavy-metal chemotherapeutic agents, and nephrotoxic drugs such as cephalosporins.
* Drugs that may cause decreased eGFR are drugs that interfere with creatinine secretion (e.g., cimetidine or trimethoprim) or creatinine assay (cephalosporins).
Procedure and patient care
• See inside front cover for Routine Urine Testing.
* Note that some laboratories instruct the patient to avoid cooked meat, tea, coffee, or drugs on the day of the test.
• Make sure a venous blood sample is drawn in a red-top tube during the 24-hour urine collection.
• Mark the patient’s age, weight, and height on the requisition sheet.
Abnormal findings
Increased levels
- Exercise
- Pregnancy
- High cardiac output syndromes
Decreased levels
- Impaired kidney function (e.g., renal artery atherosclerosis, glomerulonephritis, acute tubular necrosis)
- Conditions causing decreased GFR (e.g., congestive heart failure, cirrhosis with ascites, shock, dehydration)
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