DESCRIPTION: The metabolism of creatine and creatinine takes place in the kidneys, muscles, liver and pancreas. By structure, creatine is methylguanidoacetic acid. Creatine is a substance that makes up 98% of the total muscle mass and plays an important role in muscle contraction. It is excreted in the form of anhydride, i.e. as creatinine. Serum creatine concentration is elevated in muscle atrophy and dystrophy, and after limb amputation. Increased creatinuria is the result of impaired reabsorption of creatine in the tubules. Determining creatinine has diagnostic value only if it is a matter of muscle atrophy and regeneration in myopathies. Creatine phosphate breaks down spontaneously in muscle cells, producing creatinine. Creatinine is formed by the loss of a water molecule from creatine. Creatinine is transported through the blood plasma to the kidneys, where it is removed from the body by glomerular filtration and partial excretion in the tubules. Serum creatinine concentration depends primarily on glomerular filtration. The amount of creatinine in the plasma as well as in the urine is a fairly constant value and is related to the total muscle mass. Since creatinine is generated endogenously and is not reabsorbed in the tubules, serum creatinine is a reliable indicator of glomerular function. DETERMINATION: Creatinine concentration is determined photometrically by the Jaffe method using picric acid. The sample for analysis is serum, plasma (EDTA or heparin) and urine (24-hour or portion). Serum/plasma stability: 20°C to 25°C is 7 days, 2°C-8°C is 7 days, -20°C is one month. Urine stability: 20°C-25°C is two days, 2°C-8°C is 6 days, -20°C is six months. CLINICAL SIGNIFICANCE: In serum 1) Physiological changes in serum creatinine concentration A) After ingestion of creatinine (e.g. roasted meat) 2) Pathological changes in serum creatinine concentration A) Increased values of serum creatinine concentration in: Acute and chronic myeloid leukemia / Acute myocardial infarction / Acute pancreatitis / Acute pyelonephritis / Acute poststreptococcal glomerulonephritis / Acute renal failure / Acute and chronic leukemia / Amyloidosis / Arterial embolism and thrombosis / Bacterial endocarditis / Benign prostatic hypertrophy / Cystinosis / Diabetes mellitus / Eclampsia / Renal artery embolism / Essential hypertension / Gout / Liver failure / Hepatolenticular degeneration / Herpes Zoster infection / Hydronephrosis / Hyperparathyroidism / Hypothyroidism / Hodgkin’s disease / IgA nephropathy / Colon cancer / Bladder cancer / Prostate cancer / Testicular cancer / Uterine cancer / Cholangitis / Congestive heart failure / Chronic kidney failure / Leptospirosis / Malaria / Membranoproliferative glomerulonephritis / Multiple myeloma / Nephrotic syndrome / Polycystic kidney disease / Vomiting / Pre-eclampsia / Progressive glomerulonephritis / Progressive systemic sclerosis / Psittacosis / Reye’s syndrome / Sarcoidosis / Sepsis / Septic shock / Septicemia / SLE / Acquired hemolytic anemia (autoimmune) / Eye / Urethritis B) Reduced values of serum creatinine concentration in Anorexia nervosa / Liver cirrhosis / Eclampsia / Hyperthyroidism / Pre-eclampsia In urine 1) Physiological changes in creatinine concentration in urine: Daily excretion of creatinine in urine is constant and directly proportional to total muscle mass. Creatinine excretion in the urine increases after eating foods rich in creatinine (e.g. roast meat). 2) Pathological changes in urinary creatinine concentration A) Increased values of urinary creatinine concentration in: Acromegaly / Gigantism / Hypothyroidism / Infection / Renal vascular hypertension B) Decreased values of urinary creatinine concentration in: Active dermatomyositis / Alzheimer’s dementia / Amyotrophic lateral sclerosis / Anemia / Hyperthyroidism / Leukemia with return to normal values in remission / Muscular dystrophies / Atrophic myotonia / Paralysis / Pre-eclampsia / Progressive muscular dystrophies / Protein malnutrition / Advanced kidney diseases, before the terminal stage RISK FACTORS: Decreased values: – Daily rhythm: morning – Pregnancy (first and second trimester) Increased values: – Daily rhythm: afternoon – Fever – Increased muscle mass – Stress – shock – Trauma – Physical exertion – Starvation UTEFFECT OF DRUGS: Decreased values: amikacin, ammonium heparin, ascorbic acid, cefaclor, cephalothin, cefamandole, cefazolin, cefradine, cefuroxime, citrates, dipyrone, dopamine, etamsylate, phenacemid, methyldopa, N-acetylcysteine, norphenephrine, sarcosine Increased values: acetaminophen, acetohexamide, aminohippuric acid, ascorbic acid, azlocillin, cefaclor, cephalexin, cephaloridine, cephalothin, cefamandole, cefazolin, cefixime, cefoxitin, cefoperazone, cefotiam, cefpirome, cephradine, cefsoludin, cefuroxime, dopamine, phenolsulfophthalein, flucytosine, glycerol, glycocyamidine, lactulose, levodopa, lidocaine, lithium, methyldopa, moxalactam, nitrofurantoin, nitromethane, novaminsulfone, resorcinol, sarcosine, sulbactam, sulfamethoxazole, sulfasalazine, sulfobromphthalein, alpha-ketoglutarate, beta-Hydroxybutyrate, Creatinine in urine: ascorbic acid, asparagine, cephalothin, cefoxitin, phenolsulfophthalein, glycocyamidine, histidine, indole, levodopa, nitrofurantoin, nitrofurazone, reserpine RESULT: The reference interval depends on sex, age and work method. The reference interval is displayed with each validated result
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