Creatinine is a chemical waste molecule that is synthesised from muscle metabolism. The kidneys filter out most of the creatinine and dispose of it in the urine. Almost 2% of the body's creatine is transformed to creatinine every day. Creatinine is transported through the bloodstream to the kidneys.

The creatinine blood test is used to measure the amount of blood creatinine. The production of creatine and creatinine, depends on muscle mass, which fluctuates as creatinine is a nonprotein end-product of creatine phosphate, which is further used in skeletal muscle contraction. The normal value is 7-20 mg/100 ml. Men have a higher value than women. Value decreases by 25% during pregnancy.

Creatinine

Creatinine clearance is the elimination or clearance of creatinine from the body. Creatinine clearance (CCr) is the volume of blood plasma that is cleared of creatinine per unit time. The creatinine clearance calculation is a useful indicator in estimating the glomerular filtration rate (GFR) of the kidneys. Creatinine clearance (CCr) can be calculated on the availability of urine concentration (UCr), urine flow rate (V), and creatinine's plasma concentration (PCr). Since the product of urine concentration and urine flow rate yields creatine's excretion rate, creatinine clearance is also said to be its excretion rate (UCr×V) divided by its plasma concentration. This is represented mathematically as, Ccr = Ucr x V / Pcr

Increase in creatine levels is noticeable after meals, especially after intake of meat. Creatinine is excreted entirely by the kidneys, and therefore is directly related to renal function. When the kidneys are functioning normally, the serum creatinine level should remain constant and normal. Serious renal disorders, such as Pyelonephritis, glomerulonephritis and urinary obstruction, causes abnormal elevations in the creatinine levels.

Normal levels of creatinine in the blood are approximately 0.6 to 1.2 milligrams (mg) per deciliter (dl) in adult males and 0.5 to 1.1 milligrams per deciliter in adult females. The kidneys maintain the blood creatinine in a normal range. Creatinine is a reliable indicator of kidney function. Impairment or failure in the kidneys result in an increase in the creatinine level.

Urea is formed when protein is broken down in the body and is produced in the liver. A blood urea nitrogen (BUN) test measures the amount of nitrogen in the blood that comes from the waste product urea. BUN test is done to estimate the functioning of the kidneys. The BUN level increases, when the kidneys are unable to remove urea from the blood. Dehydration, a high protein or heart failure increases BUN level. Liver disease decreases A decreased BUN level occurs normally in the second or third trimester of pregnancy.

Blood urea nitrogen (BUN) test is done to determine the functioning of kidneys, to monitor treatment, to check out for dehydration and to identify the condition of the kidneys. An increase in the BUN level is known as azotemia and this is attributed to Dehydration, Impaired renal function, Excessive protein intake, Congestive heart failure, Acute Myocardial Infarction, Shock, Hemorrhage and Stress.