Creatine blood levels

Most doctors use the plasma concentrations of creatinine, urea and electrolytes to determine renal function. These measures are adequate to determine whether a patient is suffering from kidney disease. Protein and amino acid catabolism results in the production of ammonia, which in turn is converted via the urea cycle into urea, which is then excreted via the kidneys. Creatinine is a breakdown product of creatine phosphate in muscle, and is usually produced at a fairly constant rate by the body (depending on muscle mass). Creatinine is mainly filtered by the kidney, though a small amount is actively secreted. There is little to no tubular reabsorption of creatinine. If the filtering of the kidney is deficient, blood levels rise. 

B-10) Creatinine as a test of renal function. Creatinine, which is derived from creatine phosphate, normally is excreted almost totally by the kidney. Blood levels of serum creatinine, as well as urea, are useful indices of renal function, their elevation often being a sign of renal insufficiency. 

Creatine is a nitrogenous organic acid normally present in muscle and other tissues. When muscle is injured, creatine leaks out and can be measured in the blood as creatine kinase (CK). Blood levels of CK are increased when heart muscle is damaged, but also in muscle trauma, polymyositis, rapidly worsening cases of muscular dystrophy, vigorous exercise, or for no apparent reason. 

Creatine— A nitrogenous, organic acid found in the muscle tissue of many vertebrates. Blood levels increase when muscle is damaged. 

Enzymes, which are normally produced in cells, are released into the blood when cells are injured. For example, after a heart attack, there is an increase in blood levels of creatine phosphokinase (CPK) and other enzymes such as lactate dehydrogenase (LDH). The extent of damage and the rate of recovery can be estimated by periodically measuring the levels of these enzymes. Measurement of the MB isozyme of CPK is also used as an aid in diagnosis. 

Creatine is an amino acid but is not a component of proteins. It is made from arginine and is metabolised to creatinine prior to excretion in the urine (Chapter 44). Blood levels of creatinine and the creatinine clearance test are used to evaluate glomerular filtration in renal disease. NB Do not be confused between creatine, creatinine and carnitine. 

A number of clinical tests are available to detect kidney damage. The clinician examining a patient or the toxicologist monitoring an animal toxicity stndy collects urine and blood samples. Indications of kidney damage (which, of course, for the human patient could be related to many factors other then chemical toxicity) include urinary excretion of excessive amonnts of proteins and glucose, and excessive levels in the blood of unexcreted waste products such as urea and creatine. A number of additional kidney function tests are available to help pin down the location of kidney dysfunction. 

The synthesis of creatine. In the kidney, guanidinoace-tate is produced from arginine and glycine, then released into the blood to be taken up by the liver and methylated to form creatine (Figure 8.20(a)). The creatine is, in turn, taken up by the muscle where it is phosphorylated to produce phosphocreatine, which can maintain the ATP level, especially in explosive exercise. Creatine and phosphocreatine are converted in muscle to creatinine, which is important in clinical practice (Figure 8.20(b)) (Box 8.3). 

Apply the same reasoning to this as to the level (concentration) of any other substance in the blood -be it a drug or an endogenous chemical. An unchanging plasma creatinine means, if volume of distribution is unchanged, that input equals loss from the plasma into the urine. Creatinine comes from creatine released continuously from our muscles. In old age muscle mass is less, and the input of creatine... 

Finally, creatine supplements may be useful in the treatment of heart problems. Creatine has improved exercise capacity in patients suffering from congestive heart failure, and lowered blood cholesterol in animal studies. Limited study of creatine s effect on blood cholesterol levels in healthy humans has had mixed results, with one study reporting a positive impact and another reporting no effect at all. Further research is needed to determine if creatine is beneficial in improving blood cholesterol and preventing atherosclerosis. 

It is relevant to ask how often the routine measurement procedures currently used in laboratory medicine provide results that are traceable to high-level calibrators and reference measurement procedures (Lequin personal communication). It turns out that primary reference measurement procedures and primary calibrators are only available for about 30 types of quantity such as blood plasma concentration of bilirubins, cholesterols and sodium ion. International reference measurement procedures from the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) and corresponding certified reference material from BCR are available for the catalytic activity concentration of a few enzymes such as alkaline phosphatase and creatine kinase in plasma. For another 25 types of quantity, such... 

The patient, a 63-year-old Caucasian female, was hospitalized on 4 April 2002 though 10 April 2002 for a non-ST segment elevation myocardial infarction (non-Q-wave MI per chart documentation). She had a negative adenosine stress test after the initial event. Her serum cardiac-specific troponin I (cTnl) concentration 24 hours after her onset of chest pain was 1.4 pg/L (upper limit of normal is 0.3 ng/mL), and her creatine kinase (CK) MB level was 12.5 pg/L (upper limit of normal 6.0 ng/mL). Three days post-event her cTnl level was 0.5 pg/L and her CK-MB level was 4.5 pg/L (Fig. 5-1). MB refers to one of the isoenzyme forms of CK found in serum. The form of the enzyme that occurs in brain (BB) does not usually get past the blood-brain barrier and therefore is not normally present in the serum. The MM and MB forms account for almost all of the CK in serum. Skeletal muscle contains mainly MM, with less than 2% of its CK in the MB form. MM is also the predominant myocardial creatine kinase and MB accounts for 10%-20% of creatine kinase in heart muscle. 

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