Diagnostic use
Serum creatinine
Measuring serum creatinine is a simple test, and it is the most commonly used indicator of renal function. A rise in blood creatinine level is observed only with marked damage to functioning nephrons. Therefore, this test is unsuitable for detecting early-stage kidney disease. A better estimation of kidney function is given by calculating the estimated glomerular filtration rate (eGFR). eGFR can be accurately calculated using serum creatinine concentration and some or all of the following variables: sex, age, weight, and race.
Urine creatinine
Creatinine concentration is also checked during standard urine drug tests. Normal creatinine levels indicate the test sample is undiluted, whereas low amounts of creatinine in the urine indicate either a manipulated test or low individual baseline creatinine levels. Random urine creatinine levels have no standard reference ranges. They are usually used with other tests to reference levels of other substances measured in the urine. Diuretics, such as coffee and tea, cause more frequent urination, thus potently decreasing creatinine levels. A decrease in muscle mass will also cause a lower reading of creatinine, as will pregnancy.
Interpretation
The typical human reference ranges for serum creatinine are 0.5 to 1.0 mg/dl (about 45-90 µmol/l) for women and 0.7 to 1.2 mg/dl (60-110 µmol/L) for men. While a baseline serum creatinine of 2.0 mg/dl (150 µmol/l) may indicate normal kidney function in a male body builder, a serum creatinine of 1.2 mg/dl (110 µmol/l) can indicate significant renal disease in an elderly female. Creatinine levels may increase when ACE inhibitors (ACEI) or angiotensin II receptor antagonists (or angiotensin receptor blockers, ARBs) are taken. Using both ACEI and ARB concomitantly will increase creatinine levels to a greater degree than either of the two drugs would individually. An increase of <30% is to be expected with ACEI or ARB use.
Normal Results
Urine creatinine (24-hour sample) values can range from 500 to 2000 mg/day. Results depend greatly on your age and amount of lean body mass. Another way of expressing the normal range for these test results are:
1. 14 to 26 mg per kg of body mass per day for men
2. 11 to 20 mg per kg of body mass per day for women
Abnormal Results Mean
Abnormal results of urine creatinine are nonspecific, but may be due to any of the following conditions such as, glomerulonephritis, high meat diet, kidney infection (pyelonephritis), kidney failure, muscular dystrophy (late stage), myasthenia gravis, prerenal azotemia, reduced kidney blood flow (as in shock or congestive heart failure), urinary tract obstruction.
