Creatinine

• 2-imino- 1- methylimidazolidine -4-one
• 2-imino- 1 -methyl-1 ,5-dihydro -4H -imidazol- 4-one
• 2-imino- N- methylhydantoin

White solid

305 ° C ( decomposition)

• Moderately in water ( 90 g · l-1 at 20 ° C), soluble in ethanol
• Insoluble in diethyl ether

-238.5 KJ / mol

Template: Infobox chemical / molecular formula search available

Creatinine - in the internationalized spelling creatinine - is a metabolic product. It forms as a strongly basic amide ( lactam ) from the acid creatine in aqueous solution and in muscle tissue irreversible. In the body there is a harnpflichtiges metabolic product, so it must be excreted in the urine.

Creatinine as a metabolic parameters

Creatinine is an important renal retention parameters in laboratory medicine. The urinary excretion occurs at a relatively constant rate of 1.0-1.5 g per 24 h, most of the glomeruli, at high plasma levels partly by active tubular. However, the rate of excretion is an individual constant, in particular depending on the muscle mass and age, and thus more suitable for medical follow-up. Typical values ​​for the excretion rate are 21-27 mg/kg/24h for an age of between 20 and 30 years, 6-13 mg/kg/24h for an age of above 90 years, in children to a first approximation, the formula 15.4 0, 46 * Age ( mg/kg/24h ).

Numerous specific urinary parameters are related to the amount of creatinine excreted. This Kreatininbezug but is not suitable for all fabrics.

The blood plasma level is about 0.7 mg/100 ml ( 50 to 120 micromol / l ), but also depends on factors such as muscle mass, physical activity, age, gender, and renal function. Important for the evaluation of renal function is that of creatinine only at a restriction of the glomerular filtration rate ( GFR) greater than 50 % increase, or only becomes significant. This includes a "normal" creatinine incipient renal insufficiency not.

In laboratory medicine one takes the determination of creatinine clearance (CrCl ) advantage in order to calculate the GFR can. Creatinine is not reabsorbed tubular design, which means that virtually every molecule filtered ultimately appears in the urine. Since the plasma concentration of creatinine is not constant (see above), in addition to the 24 - h urine also requires a venous blood sample in order to make precise statements about the GFR can.

A simpler, but less accurate estimation of GFR is given by the sole determination of plasma creatinine concentration. It makes use of a nonlinear relationship between GFR and the concentration in the blood plasma advantage. Both in the formula of Donald W. Cockcroft and Gault Henry ( Cockcroft -Gault formula ), as well as in the more recent of Mawer, Björnsson, Hull and Martin walk a further yet gender, age and body weight. The 1999 was developed by the Modification of Diet in Renal Disease Study Group ( MDRD ) MDRD formula not consolidated in body weight. In children, the Schwartz formula is well suited for the determination of GFR.

Even medicines can affect your creatinine level, so this is, for example, increased by opiates and diuretics. In contrast to creatinine creatine for muscle building is completely meaningless.

Creatinine excretion

The excretion of creatinine takes place through the kidneys. A measure of the excretion by the kidney (Latin ren ) is the renal clearance. In determining means of urine collection for creatinine clearance is calculated as follows:

With

The Cockcroft -Gault formula provides an estimate of the creatinine clearance:

With

In the following cases, the creatinine clearance may be too low:

• Kidney disease
• By fluid loss (diarrhea, vomiting, thirst, shock), kidney damage
• Excessive meat supply
• Prolonged physical work before venipuncture

And in this too high:

• In the early stage of diabetes mellitus
• Pregnancy