Creatinine is a break-down product of muscle metabolism in the body. It is produced in the body at a constant rate and is excreted through urine. Creatinine is not reabsorbed into the body from the kidneys. Hence, any failure on the part of the kidneys to excrete creatinine results in rise of creatinine levels in the blood. Variations from normal creatinine levels could indicate kidney dysfunction and muscle problems (like rhabdomyolysis). Hence, tests are conducted to find out creatinine levels in blood and the amount of creatinine expelled through urine. These tests are usually performed as screening tests for evaluating kidney function.
Why to Check Urine Creatinine Level
As mentioned above, variations in normal creatinine levels may indicate some problem with the functioning of kidneys. So, urine creatinine levels are checked to evaluate the functioning of kidneys and to detect the underlying causes. Level of creatinine in urine is also checked as a part of standard drug tests. This is done to find out whether the sample has been diluted for tampering the results. If the level of creatinine in the sample is normal, then, it is considered undiluted. If the level is low, then, it is concluded that the person may have a very low creatinine level or the sample was diluted.
How is Urine Creatinine Level Checked
We all know that in order to find out the level of creatinine in urine, a sample of urine has to be tested. Random urine creatinine tests are usually used with other tests (like urine protein test). This is because, there is no standard reference ranges for random urine creatinine test, as the level of creatinine may fluctuate throughout the day. Urine creatinine levels may vary with intake of certain foods, medication and beverages. Even intake of large amounts of fluids may reduce the concentration of creatinine in urine, for some time.
So, serum (blood test) creatinine test and/or creatinine clearance test is conducted, for evaluating kidney functioning. Both blood and urine samples, collected over a period of 24 hours, are required to conduct creatinine clearance test. Creatinine clearance value refers to the volume of blood that is cleared of creatinine, per unit of time (like a minute). The concentration of creatinine in blood and urine sample, along with the rate of urine flow is used to calculate creatinine value. Even the body surface area (calculated with body weight and height) and amount of muscle mass may be taken into consideration, while calculating the accurate value. As it is cumbersome to collect the urine excreted over a period of 24 hours, creatinine clearance test may not be preferred by many. Even if you collect a 24-hour urine sample, the test may get void, if the clearance value is abnormally low or high. But, if the serum creatinine level is found to be unreliable, then, creatinine clearance test is conducted.
Normal Creatinine Levels in Urine
The normal urine creatinine level may vary with age, muscle mass and gender. It is also said that increased intake of dietary protein as well as strenuous physical activities may increase the levels of urine creatinine. Men tend to have slightly elevated creatinine levels in urine, as compared to women. This is because of the presence of more skeletal muscle mass in men, as compared to the fairer sex. The rate of muscle metabolism slows down with age, and so, elderly people have low creatinine levels in urine. Some medicines are also known to affect the levels of creatinine. As there is no standard reference range for random urine creatinine levels, a 24-hour urine sample test is often relied upon, to find out creatinine levels.
- The normal level of urine creatinine in case of a random test may range between 40 to 300 mg/dL in males and 37 to 250 mg/dL in females.
- In case of a 24-hour urine sample test, the normal creatinine level could be anywhere between 500 to 2000 mg/day.
- Urine creatinine level (from a 24-hour sample) may also be given on the basis of body mass. In that case, the normal value for men may range between 14 to 25 milligrams per kilogram of body mass, for a day. For women, the value may be between 11 to 20 milligrams per day.
- In case of creatinine clearance test, clearance value may range between 97 to 140 ml per minute (in men) and 88 to 128 ml per minute (in women).
(In case of normal healthy women, the blood creatinine levels may range between 0.5 to 1.1 milligrams/deciliters. For healthy men, it will be between 0.7 to 1.3 mg/dL. The blood creatinine levels can be between 0.5 to 1.0 mg/dL in teenagers, 0.3 to 0.7 mg/dL for children and 0.3 to 1.2 mg/dL in newborns. In people with a single kidney, the normal range may be around 1.8 or 1.9 mg/dL.)
Interpretation of Results
Abnormal urine creatinine levels may be due to any of the following medical conditions that affect the kidneys or muscles. Drastic variations in normal creatinine level may indicate urinary tract obstruction, kidney failure, glomerulonephritis, rhabdomyolysis, muscular dystrophy, reduced blood flow to the kidneys, prerenal azotemia, myasthenia gravis and pyelonephritis.
Abnormal creatinine clearance value may indicate dehydration, kidney failure, severe kidney disease, shock, renal outflow obstruction, acute tubular necrosis and congestive heart failure. Intake of certain drugs and consumption of huge amounts of meat, are other factors that may affect the creatinine levels in urine. While low creatinine levels in blood can be caused by muscular dystrophy, myasthenia gravis or aging, it could also be a symptom of some liver disease or due to a low-protein diet. Pregnant women may also have low blood creatinine levels. A blood creatinine level above 2.0 mg/dL in children and above 10 mg/dL in adults indicate severe kidney impairment.