Biochemical blood test: preparation, table of normal values, decoding

A biochemical blood test is a detailed examination of a patient's venous blood to evaluate the function of internal organs, detect deficiencies in vitamins, enzymes, macro- and micronutrients, and diagnose metabolic abnormalities. Blood biochemistry is more indicative than the general clinical analysis, and the results of the analysis allow detecting many diseases at an early stage. That is why this examination is recommended not only by doctor's prescription, but also for preventive purposes at least once a year. The results of the biochemical blood test include many related indicators and should be interpreted by a doctor - self-medication is dangerous to your health! 

How to prepare for the procedure?

• Blood sampling for a biochemical test is always done on an empty stomach, most often between 8 a.m. and 11 a.m. Non-carbonated water is allowed on the day, and the day before the procedure you should exclude heavy food, carbonated drinks, strong coffee, tea, and alcohol from your diet.
• In the last hour before the blood test you should not smoke.
• Immediately before the procedure, try to avoid physical and emotional stress, the last 10-20 minutes is better to just sit near the manipulation room.
• If the date of the biochemical blood test falls on the period of medical treatment or physiotherapy, it is worth to consult a doctor - perhaps he will recommend to postpone the study to another time or to interrupt the course of treatment for a few days.

Decoding of the results of the biochemical blood test

New generation laboratory analysers are able to provide results as early as two hours after a blood sample has been taken. Typically, the patient receives the results within 2-3 days in the form of a printed or electronic table listing the parameters studied, their values and the reference (average) ranges of the norm. Different laboratories offer different amounts of data, and this article will describe the most commonly tested blood values.

Proteins 

Total protein characterises the status of protein metabolism and reveals dysproteinemia (changes in the quantitative ratio of protein fractions in the blood serum). Low values may indicate malnutrition, liver disease, burns, trauma, and surgery, while elevated values may indicate infectious disease, non-infectious hepatitis, autoimmune disease, dehydration, or may be caused by diarrhea and vomiting. 

Protein albumin occupies up to 65% of blood plasma volume, is produced by the liver and performs the most important function of transporting many biologically active substances. The reasons for a decrease in albumin concentration are the same as those for total protein. The value rises quite rarely, for example, during dehydration, hemoconcentration or due to anabolic steroids. 

The iron-containing protein myoglobin is tested primarily for the early diagnosis of myocardial infarction. High concentration of myoglobin may indicate myocardial infarction, heart failure, acute kidney injury, consequences of thermal burns, electric shock. Low myoglobin accompanies the course of rheumatoid arthritis and poliomyelitis. 

The value of glycated or glycosylated hemoglobin is very important for patients with diabetes and is also used for its diagnosis. Glycated hemoglobin gives an idea of the average blood glucose level over a long period of time (1-2 months). If the concentration of this protein fraction does not exceed 5.7% of the total hemoglobin in the blood, we can talk about a compensated state. Values in the range of 5.7-6.4% indicate the risk of developing diabetes mellitus, and values above 6.4% indicate severe decompensated diabetes. 

C-reactive protein acts as an indicator of inflammation in the body. Exceeding the threshold of 0.5 g/l indicates acute inflammation or malignancy. This parameter is also important in evaluating the effectiveness of antibacterial and anti-inflammatory therapy. 

The values of transferrin, ferritin, and serum iron-binding capacity are used to diagnose abnormalities of iron metabolism in the blood. Transferrin is the main carrier of iron, and elevated concentrations are usually indicative of iron deficiency anemia and decreased concentrations are indicative of infections, cirrhosis, other anemias, or protein starvation. Conversely, in iron deficiency anemia, ferritin decreases and increases indicate inflammation, liver disease, or oncopathology. 

Lipids

Total cholesterol is used to detect primary and secondary lipid metabolism disorders, to assess the likelihood of atherosclerosis development, and to evaluate the effectiveness of treatment of atherogenic lipid metabolism disorders. Low values are caused by cachexia, starvation, malabsorption, severe acute diseases, liver failure, hyperthyroidism, and increases are caused by primary and secondary dyslipoproteinemia. Dangerous consequences of low cholesterol are psychophysiological disorders and reproductive dysfunction, high - diabetes and atherosclerosis. Biochemical blood tests for triglycerides (products of carbohydrate metabolism in the liver) have the same objectives, and the causes of their rising and falling concentrations are also the same as for total cholesterol. 

High- and low-density lipoprotein cholesterol (HDL and LDL, respectively) are examined and interpreted in conjunction with total cholesterol and triglycerides for a more accurate diagnosis. HDL is elevated in primary biliary cirrhosis, hepatitis, alcoholism, or its increase may be genetically determined. In patients with atherosclerosis, decompensated diabetes, chronic kidney disease, cholestasis, the value of HDL decreases. Low-density lipoproteins are involved in the processing and excretion of fats, and a decrease in their concentration may indicate the development of chronic anemia, Raynaud's syndrome or myeloma, and an increase - hypothyroidism, nephrotic syndrome, diabetes, porphyria, Cushing's syndrome, the risk of atherosclerosis. 

Carbohydrates 

Glucose is the main source of energy for all cells and tissues of the human body and, in particular, the only source of energy for the brain. The value of glucose in the results of a biochemical test reflects the level of sugar in the blood. If this value is elevated, there is a possible risk of diabetes mellitus, central nervous system damage, and hormonal disorders. Glucose "drops" when tumors form in the pancreas, when there is hepatic and adrenal insufficiency, hypothyroidism, malnutrition or due to insulin intake. 

The value of fructosamine reflects fluctuations in blood glucose levels in the period of 2-3 weeks preceding the test. If its concentration exceeds 280-285 μmol/l, the doctor considers the possibility of developing diabetes mellitus. 

Inorganic substances and vitamins 

Vitamin B12 in the human body is involved in, among other things, the production of red blood cells. High levels of this vitamin can indicate liver or kidney disease or leukemia. Diseases of parasitic etiology, inflammatory processes in the gastrointestinal tract and following a vegetarian (vegan) diet, by contrast, lead to lower levels of vitamin B12 in the blood. 

It was mentioned in a previous paragraph that iron is involved in the transport of oxygen. Its deficiency is usually due to poor diet or metabolic disturbances, and its overabundance is due to functional disorders of the intestine. 

Potassium is responsible for the regulation of water balance and normalizes heart rhythm. Potassium deficiency occurs due to improper or insufficient diet, vomiting, renal failure, Cushing's syndrome, osmotic diuresis, chronic kidney disease, as well as accompanying prolonged use of steroid drugs. Potassium increases in acute dehydration, extensive trauma and burns, chronic adrenal insufficiency, diabetic coma or due to potassium-saving diuretics. 

Calcium is involved in the formation of bone tissue and is essential for normal muscle, nerve, heart muscle, and vascular function. Low blood calcium values indicate vitamin D deficiency, functional kidney disease, pancreatitis, impaired magnesium metabolism or hypoparathyroidism. Elevated calcium levels accompany hyperparathyroidism or are a symptom of oncopathology. 

Magnesium performs the function of intracellular metabolism and transmission of impulses from nerve endings to muscles. Malnutrition, impaired absorption, prolonged diarrhea, colitis, enterocolitis and dyspepsia lower the concentration of magnesium in the blood. Functional kidney disorders, hypothyroidism, lactate acidosis and neoplasms lead to an increase. 

In addition to magnesium, sodium, which also participates in calcium metabolism, is responsible for transferring impulses to muscles. Hypothyroidism, Addison's disease, diabetes mellitus, kidney and gastrointestinal diseases, congestive heart failure, intake of gentamicin, and less frequently, Parchon's syndrome or hypercalciuria may be the cause of sodium reduction. High sodium values in biochemistry results indicate dehydration, salt oversaturation, non-sugar diabetes, or kidney disease with oliguria. 

Normal function of the nervous and musculoskeletal systems is impossible without sufficient phosphorus in the body. Blood phosphorus content increases with hypoparathyroidism, excessive vitamin D, rhabdomyolysis, bone disease or improper diet, less often with acromegaly. On the other hand, hypovitaminosis D, hyperparathyroidism, kidney transplantation, intravenous glucose infusions, and respiratory alkalosis cause decreased blood phosphorus concentrations. 

Chlorine functions to maintain blood acid-base balance and osmotic pressure. The most obvious causes of decreased chlorine levels are profuse sweating, vomiting, diarrhea, improper treatment with diuretics, less often the decrease is caused by nephrotic syndrome and hypokalemic metabolic syndrome. Excess chlorine in the blood can be a consequence of dehydration, edema, alkalosis and decompensation of cardiac activity. 

Low molecular weight nitrogenous substances 

Urea and creatinine are tested together, and their values reflect the functional state of the patient's kidneys, in particular the degree of impairment of filtration and excretory functions. High values indicate kidney problems, but may be due to excessive exercise, a high-protein diet, prolonged fasting, or thyroid disease. Low urea values may be due to a low-protein diet, pregnancy, and liver disease. 

Uric acid levels, as an auxiliary parameter, reflect the body's ability to eliminate waste products of nucleic acid and purine metabolism processes. It is of particular diagnostic interest for patients with gout. The main causes of elevated uric acid are gout and alcoholism, less often - kidney and liver pathology. Low values of uric acid in the results of biochemical blood tests are much less common and usually indicate an improper or insufficient diet. 

Pigments

The yellow pigment bilirubin begins to accumulate in the blood in diseases and hereditary pathologies of the liver, biliary tract, for example, in Gilbert syndrome. Indirect bilirubin may also be elevated in some anemias and malaria. 

Enzymes

A liver enzyme with the difficult-to-pronounce name alanine aminotransferase is involved in amino acid metabolism. It is elevated in myocardial infarction, acute hepatitis A and B, and other liver diseases. 

The enzyme amylase is produced by the salivary glands and pancreas and is responsible for the digestion of carbohydrates. An excess of 3-5 times the normal value may indicate acute appendicitis, peritonitis, gastric and duodenal ulcer, and cholecystitis. In acute pancreatitis or exacerbation of its chronic form the amylase value increases by 10-30 times. Elevated pancreatic amylase value allows timely detection of complications of abdominal surgery and pancreatic diseases. 

The concentration of aspartate aminotransferase enzyme in human blood increases greatly in case of liver or cardiac muscle damage, due to alcohol abuse the values may increase twice as much as normal. 

High values of gamma-glutamyltransferase enzyme are observed in patients with acute hepatitis, extra- and intrahepatic cholestasis, alcoholism, pancreatic and prostate cancer, and primary liver tumors. 

Increased concentration of creatine kinase in blood may indicate myocardial infarction, muscle damage of different genesis, and renal failure. Lactate dehydrogenase is elevated in diseases of the cardiovascular system, liver and kidneys, and in pregnant women. High values of lipase are observed in patients with acute pancreatitis, intestinal infarction, biliary colic, wounds, fractures, and breast cancer. Phosphorus metabolism in the body is directly related to alkaline phosphatase - its increase accompanies acute viral and alcoholic hepatitis, cirrhosis, mononucleosis, liver cancer or liver metastases. Cholinesterase is decreased in cirrhosis, liver failure, hepatitis, and myocardial infarction. Cholinesterase values are also indicated in patients taking muscle relaxants.