Creatinine

 Creatinine

Chemistry- It is the anhydride of creatine.

Source- It is mostly formed from breakdown of creatine phosphate in the body. This process is not catalysed by any enzymes and is irreversible.

Effects of Creatinine feeding-When orally administered nearly 80% is promptly excreted in the urine. Hence, it is considered to be a waste product. It is a no-threshold substance. It is filtered by the glomeruli and is also actively secreted by the tubular cells in the urine. Amount in blood-Normally it is present about 0-7-2-0 to be pathological when its value increases about 2 mg. Creatinine is also found in bile, sweat and in secretion of stomach and intestine.

Excretion-about 1.2-2.0 gm in adult males and 0.8-1.5 gm in adult females are excreted in 24 hours. The amount excreted is remarkably constant for a particular individual. Creatinine is related to the muscle bulk and is higher in muscular persons. This stands in great contrast with creatine excretion, which bears no relation to muscular development. The excretion increases during work and exercise but is immediately followed by a fall, so that the daily output remains constant.

Significance- Creatinine represents the waste products of creatine metabolism and it arises in the body from the spontaneous breakdown of creatine phosphate. It serves practically no function in the body apparently. As its excretion is not related with food protein so its variations in the excretion indicate some of the metabolic disorders. Appearance of creatinine in urine is known as creatinuria when a small amount of creatine is also excreted along with creatinine. The creatine value gradually decreases as the maturity is advanced. Its excretion increases in fevers, starvation, on a carbohydrate-free diet and in diabetes mellitus. It may increase due to excessive tissue destruction releasing creatine or due to failure of creatine being properly phosphorylated. So creatinine excretion is independent of food proteins and is to be considered as an index of endogenous protein metabolism.

Creatinine coefficient

It is the creatinine and creatine coefficient which represents the ratio of amount of creatinine and creatine excreted in mg per Kg of body weight per day and the value normally averages 20-26 for men and 14-22 for women.

BUN to Creatinine Ratio

Both urea (BUN) and creatinine are freely filtered by the glomeruli; however, urea reabsorbed by the tubules can be regulated -increased or decreased, whereas creatinine reabsorption remains the same-minimal reabsorption. BUN-to-creatinine ratio is the ratio of two serum laboratory values, the blood urea nitrogen (BUN) (mg/dL) and serum creatinine (Cr) (mg/dL). The reference interval for normal BUN/creatinine serum ratio is 12:1 to 20:1.