Creatinine is derived from the metabolism of creatine phosphate in skeletal muscle and to a smaller degree from dietary meat intake. Is is filtered out of the blood by the kidneys. It is released into the circulation at a relatively constant rate and has a stable blood plasma concentration. If the filtering of the kidney is deficient, blood levels rise.
Why Test Serum Creatinine?
Kidney function is best measured by testing the serum creatinine, sometimes called serum creatine. Healthy kidneys filter creatinine and other waste products from your blood and these waste products exit your body in the form of urine. According to mayoclinic.com, if you have diabetes, kidney disease, or an illness that affects your kidneys, you should have serum creatinine tests done according to the illness that you have.
Normal Values
Serum creatinine levels depend on the Glomerular Filtration Rate (GFR) of the kidneys. If the kidneys are not filtering the blood as they should, the serum creatinine rises. There are ranges of normal values for serum creatinine. According to rnceus.com, adult males range from 0.8 - 1.4 mg/dl, adult females range from 0.6 - 1.1 mg/dl and children range from 0.2 - 1.0 mg/dl. Muscle mass makes a difference in values of serum creatinine because those with more muscle break down more creatine phosphate, increasing circulating creatine in the blood.
Procedure for Testing
Serum creatinine levels are tested by drawing blood from a vein by a needle or by using a lancet to puncture the skin to make it bleed and collecting in a pipette. According to nlm.nih.gov, the site is cleaned with alcohol or antiseptic. An elastic band is then placed around the upper arm to make the vein swell with blood. Next, the needle is inserted into the vein, and a collection tube is attached to the needle to collect the blood. The band and needle are then removed and a pressure dressing is applied to the site.
Test Preparation
Preparation for serum creatinine testing depends on whether you are taking any medications that may affect the values of the test. According to nlm.nih.gov, certain drugs like aminoglycosides, cimetidine,
heavy metal chemotherapy drugs, and select antibiotics may affect the results of the creatinine level.
Serum Creatine and BUN
Serum creatinine is usually used along with the BUN (blood urea nitrogen) test to assess kidney function. According to labtestsonline.org, BUN and creatinine are usually ordered as part of a metabolic panel, but may be done separately to assess kidney function. The principle behind this ratio is the fact that both BUN and creatinine are freely filtered by the glomerulus, however urea reabsorbed by the tubules can be regulated, whereas creatinine reabsorption remains the same.
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