Creatine is synthesized from amino acids in the kidney, liver and pancreas. The creatine is then transported in the blood to other organs where it is synthesized into creatinine.
In the absence of kidney disease, the urinary creatinine is excreted in rather constant amounts and represents glomerular filtration and active tubular excretion of the kidney.
Because the creatinine is excreted from the body at a constant rate, there are expected values for creatinine in normal human urine. Specimen validity testing is the evaluation of the specimen to determine if it is consistent with normal human urine (creatinine values greater than 20 mg/dL). When abnormally large quantities of fluids are consumed, the urine becomes diluted and the creatinine levels are substantially reduced. At the same time, the dilution of the urine reduces the amount of drugs and their metabolites that may be present. Alternately, a donor may try to beat a test by adding water to the urine cup to dilute the drug level. San Diego Reference Laboratory offers the test for creatinine as part of the routine drug panels. The creatinine result is reported as mg/dL and each result will have one of the following messages attached:
- Consistent with normal human urine
(If the creatinine value is greater than 20mg/dL.)
- Possible diluted urine sample.
(If the creatinine value is between 6 and 20mg/dL.)
- Possible substituted urine sample.
(If the creatinine value is 5mg/dL or less.)
- Joseph E. Graas, Ph.D., Technical Director
- Carolyn Hammock, MT(ASCP), CLS, QA/QC Officer