Creatinine blood test – biochemical analysis aimed at measuring one of the main products of nitrogen metabolism – 1-methylglycocyamidine, which reflects the state of protein metabolism in the body. The study of creatinine concentration in the blood is performed in conjunction with other biochemical parameters and in the Rehberg sample. Creatinine blood test is carried out to detect renal dysfunction, evaluate the effectiveness of treatment of diseases of internal organs and acute conditions, as part of a preoperative examination. Venous blood is used for analysis, and the photokinetic method (Jaffe reaction) is most often used in laboratory practice. In a healthy adult, the creatinine level in the blood ranges from 50 to 111 mmol/l. The timing of the analysis is no more than a day.
Creatinine is formed in the muscles during the contraction of muscle fiber, being the end product of the breakdown of creatine phosphate. In the future, it diffuses into the blood and is excreted by the kidneys with urine. Creatinine belongs to the group of waste substances (nitrogenous slags) and, with an increased content in the blood, has a toxic effect on organs and tissues. The rate of creatinine formation in the muscles and excretion by the kidneys in the urine determines the degree of its concentration in the blood. Measurement of creatinine in the blood is used in clinical diagnostics, primarily to assess the excretory function of the kidneys and the degree of damage to muscle tissue.
Creatinine blood test is the “gold” standard in such areas of medicine as therapy (nephrology, cardiology, gastroenterology, endocrinology, neurology, genetics) and pediatrics – its study is necessary for the diagnosis of diseases, determining the severity of the pathological process, evaluating the effectiveness of treatment. In the medicine of “critical conditions” (anesthesiology-resuscitation, surgery, traumatology), this analysis is used to determine indications for urgent surgical intervention and efferent methods of treatment (hemodialysis). To more accurately determine the glomerular filtration rate and assess kidney function, the Rehberg test is used, based on determining the ratio of creatinine concentration in blood and urine, taking into account the gender, weight and age of the patient.
Indications and contraindications
Creatinine blood test can be prescribed with a decrease in the amount of urine excreted, swelling of the face, legs, lumbar region, an increase in the volume of the abdomen – these symptoms may indicate fluid retention in the body as a result of impaired excretory kidney function, the development of peripheral edema and ascites. The study of creatinine in the blood is performed for dysuric disorders: frequent urination at night, unpleasant sensations during urination (pain, itching, burning, intermittent jet), altered color and transparency of urine (red, brown, cloudy), high blood pressure; fever, pain in the kidney area (lumbar region, under the ribs along the spine), which may indicate obstructive diseases of the urinary tract and kidney tissue damage, leading to impaired blood supply to the kidneys and their ability to filter urine qualitatively.
Creatinine blood test is indicated for unexplained complaints of weakness, fatigue, dizziness, nausea, absent-mindedness, memory impairment, decreased appetite, sleep disorders, pain and muscle weakness, which may indicate possible poisoning with poisons, overdose or toxic effects of drugs leading to the “slagging” of the body with protein breakdown products.
In polyclinics, outpatient clinics and dispensaries, the study of creatinine in the blood is prescribed during the annual medical examination of the population, before the upcoming planned hospitalization, computed tomography and MRI with contrast. The analysis is carried out within the framework of diagnostics and in order to monitor the effectiveness of treatment of diseases of the urinary, muscular, endocrine and cardiovascular systems, drug diseases; to assess the degree of renal insufficiency. In the antenatal clinic, the creatinine level in the blood is assessed during pregnancy.
In hospitals and hospitals, the study of creatinine in the blood is used for screening examination during planned and emergency admission of patients, including before surgery; to determine the degree of decrease in glomerular filtration in acute and chronic renal failure caused by both renal and extrarenal causes; in severe injuries and burns with a large percentage of skin and muscle damage, septic conditions; in shocks of any etiology; during courses of hemodialysis and other efferent methods of treatment to analyze their effectiveness.
There are no contraindications to prescribing a creatinine blood test.
Preparation and blood collection
For the study, blood taken before 11:00 am is used. Blood sampling is performed in the laboratory, the treatment room of a polyclinic or inpatient department from the ulnar or any central vein. In many cities there are medical services that can go to the patient’s home for blood collection.
In order for the results of the analysis to be as reliable as possible, it is necessary to follow several recommendations. 24 hours before taking the analysis, do not expose yourself to exhausting physical exertion, do not eat heavy protein foods in large quantities; 12 hours before – stop eating, drink only clean water; 30 minutes before the study, do not smoke and try to avoid stress.
Blood collection is carried out in a regular dry clean test tube or a vacuum tube with a lid. The identification number, time and place of blood collection are indicated on the test tube. Before transferring the test tube to a courier or laboratory assistant, the blood is stored in the refrigerator at a temperature of (+2)–(+4)°With or in special containers. The blood should be delivered to the laboratory on the same day. In the laboratory, protein particles are removed from the blood serum, and then a reagent is added – picric acid, which binds to serum creatinine and turns the solution orange-red. Further, its concentration is determined by the photokinetic method.
The determination of creatinine by the Jaffe reaction is not strictly specific, since picric acid can bind some nonsteroidal anti-inflammatory drugs, ascorbic acid, excess glucose and fructose in the blood, acetone, antibiotics of the cephalosporin group, antiparkinsonian agents, nitrofurans. Taking these drugs can give a “false” increase in creatinine levels, so this specificity should be taken into account when interpreting the results.
The study is carried out within 6-24 hours after taking the analysis, in the hospital in emergency cases – within 1-2 hours. Creatinine blood test is usually prescribed in combination with a urea test. The joint interpretation of the two indicators makes it possible for a medical professional to assess the degree of renal dysfunction and muscle tissue damage as accurately as possible.
Normally, a certain amount of creatinine is always in the blood, since the breakdown of protein molecules in the human body is a constant process. The unit of measurement of creatinine is micromol/l (micromol per liter).
In children under one year, the creatinine level in the blood is 30-48, from 1 to 6 years – 31-52, from 6 to 11 years – 36-63, from 11 to 15 years – 46-72, from 15 to 20 years – 51-92 mmol / l. In women aged 20 and older, creatinine in the blood is determined at the level of 50-98, in men – 64-111 mmol / l. Due to less pronounced muscle mass, creatinine concentration in women is usually lower than in men; in hypersthenics it is higher than in asthenics. In the population over 60 years of age, due to concomitant diseases leading to a decrease in glomerular filtration, the creatinine level becomes slightly higher.
A slight (physiological) change in the level of creatinine in the blood may be associated with intense physical exertion; emotional experiences immediately before blood collection; eating a large amount of protein (meat, eggs, fish, dairy products, protein shakes); pregnancy, taking certain medications.
Increased creatinine levels
With significant changes in the level of creatinine in the blood to a greater extent, first of all, the insufficient possibility of removing creatinine from the body as a result of kidney diseases, due to a decrease in their filtration function, is excluded. Such pathologies include: acute and chronic glomerulonephritis, pyelonephritis, tuberculosis and amyloidosis of the kidneys, primary benign and malignant kidney tumors, urolithiasis.
Conditions and diseases associated with massive breakdown of muscle tissue (rhabdomyolysis) can increase the concentration of this metabolite: extensive muscle damage from injuries, crash syndrome (prolonged compression syndrome), dermatomyositis. The reason for the increase in creatinine in these cases is the accelerated breakdown of protein molecules. Taking statins, well-known drugs for lowering cholesterol levels in the blood, can lead to rhabdomyolysis. Creatinine in the blood increases with extensive myocardial infarction, arterial hypertension, myocarditis, acute and chronic heart failure.
An increase in indicators can occur against the background of a malignant neoplasm, leukemia, a benign tumor of the thymus. In these processes, the cause of hypercreatininemia is high protein catabolism. The causes of an increase in creatinine levels in the blood can be bleeding of their gastrointestinal tract, intestinal obstruction, injuries and burns, accompanied by a state of shock against the background of a large loss of blood and dehydration. In all these cases, the production of cortisol increases, as a result of which the process of protein breakdown increases and kidney perfusion decreases.
Hypercreatininemia is possible with thyrotoxicosis and treatment of hypothyroidism with thyroxine. A change in the indicators in a big way can occur against the background of a kushingoid condition associated with hyperplasia of the adrenal cortex or prolonged intake of adrenal cortex analogues (dexamethosone, prednisole). Taking antibiotics (tetracyclines, cephalosporins), aspirin, some diuretics, cytostatics, and anabolic steroids can increase the concentration of this compound in the blood. The reason for the increase in creatinine in the blood with the development of renal insufficiency in the 3rd trimester of pregnancy may be a deterioration in kidney perfusion as a result of compression by the fetus and activation of cortisol production.
Reduced creatinine levels
The reasons for the decrease in creatinine in the blood may be anorexia (complete refusal to eat), a low-protein vegetarian diet, hereditary and acquired myodystrophy with concomitant muscle atrophy, conditions after limb amputation. A transient decrease in creatinine levels in the blood can be observed during pregnancy due to an increase in blood volume and renal filtration, especially in the 1st and 2nd trimester, as well as after a hemodialysis session.
The reasons for the decrease in creatinine in the blood may be diseases associated with impaired production of vasopressin (antidiuretic hormone) in the hypothalamic-pituitary zone, as a result of which the amount of urine produced decreases and pathological hyperhydration develops.
Treatment of abnormalities
It should be remembered that the detected deviation of the creatinine level in the blood from the norm cannot be regarded as a diagnosis. The doctor should analyze the results of the study on the basis of cumulative laboratory data, symptoms, anamnesis and additional examination methods. Based on the data obtained, the doctor will decide in which conditions it is more desirable to be examined, monitored and treated.
With a prolonged and persistent increase in creatinine, especially in the case of primary detection of hypercreatininemia, hospitalization to one of the specialized departments is indicated, where a more thorough examination will be carried out and specific treatment will be prescribed. If the creatinine concentration is more than 500-600 mmol / l, then there are all indications for hemodialysis (“artificial kidney”).
To reduce the level of creatinine in the blood, it is important to follow a diet that should include a large amount of vegetables and fruits, vegetable oils. The amount of protein consumed (meat, fish, sausages, dairy products, mushrooms) is limited. It is necessary to exclude from the diet everything salty, fried, spicy and strong (alcohol, coffee). If a renal pathology is diagnosed, then the drinking load should be reduced to 1-1.2 liters per day. In other conditions, drinking enough water will help reduce creatinine levels. Depending on the general condition of the patient, walking in the fresh air and light physical activity are not contraindicated.