A blood test is one of the basic tests most often recommended by doctors. Its results allow assessment of the patient’s general health condition and, if necessary, allow to plan an appropriate treatment.
Peripheral blood is taken from the blood vessels, mainly capillaries, arteries and veins. Peripheral blood is collected from the blood vessels, mainly from the capillaries, arteries and veins, and analyzed for the formed blood elements such as red and white blood cells, platelets and plasma.
The tests of the formed elements of the blood include:
- Peripheral blood count – this is a basic diagnostic test that involves qualitative and quantitative evaluation of blood elements. This test determines indicators such as:
- RBC – an indicator that determines the number of red blood cells,
- MCV – the mean volume of red blood cells,
- MCH – an indicator that determines the average mass of hemoglobin in a red blood cell,
- MCHC – an indicator that measures the average concentration of hemoglobin in erythrocytes,
- WBC – an indicator that determines the number of white blood cells,
- PLT – an indicator that measures the number of platelets per mm3 of blood,
- HGB or Hb – hemoglobin concentration,
- Hct – hematocrit, which is the ratio of the volume of coagulated erythrocytes to the total blood volume,
- RDW – red blood cell volume variation,
- many other, less frequently assessed indices.
- Peripheral blood smear, also referred to as leukocytogram – determines the number of individual white blood cells,
- Tests that evaluate the properties of specific types of blood elements:
- red blood cells, such as the activity of enzymes within the cells or the resistance of the cell membrane to changes in osmolality,
- white blood cells, e.g., intracellular enzyme activity, migration capacity, phagocytic activity, or the presence of specific antigens on specific cell types
- platelets, e.g. platelet adhesion and aggregation capacity, platelet factor activity,
- cytogenetic examination of nucleated blood cells.
A test involving the analysis of plasma components is referred to as a blood biochemical test. It provides valuable information on:
- concentration of metabolic end products, such as nitrogen, uric acid, ammonia, urea,
- electrolytes: sodium, magnesium, calcium, chlorine, potassium and others,
- glucose levels,
- lipids – total cholesterol, triglycerides,
- protein, albumin and globulin,
- activity of many enzymes, among others: alanine aminotransferase, alkaline phosphatase,
- blood coagulation system,
- pituitary and peripheral endocrine hormones,
- presence of specific antibodies,
- tumor markers,
- the concentration of drugs, metals and alcohols,
- presence of chemical and plant toxins,
- concentration of compounds accumulating in the blood as a result of metabolic congenital disorders, e.g. phenylalanine in phenylketonuria,
- presence and concentration of other substances, e.g. vitamins.
In addition, frequently performed tests in the analysis of blood properties are:
- Biernacki’s reaction, or ESR – this is a laboratory test measuring the path of descent of red blood cells in uncoagulated blood over a period of 1 hour, is an indicator of cancer, inflammatory and rheumatic processes,
- bleeding time – it is a diagnostic test that determines the time between the moment of damage to the skin, which causes the outflow of blood and the moment when the outflow stops, bleeding time shows the ability of platelets and small blood vessels of the skin to form a clot,
- Thrombin time – is an indicator of the clotting time of citrated plasma with the addition of a standard solution of thrombin, which has the ability to convert soluble fibrinogen into insoluble fibrin, thrombin time testing is important in controlling anticoagulant or fibrinolytic treatment.Blood analysis can also be used to assess the acid-base balance of the blood. With the help of this test, the following parameters are evaluated: blood pH, carbon dioxide concentration in the blood, free hydrogen ion concentration, bicarbonate ion concentration in the blood, sum of the concentrations of all the buffer anions in the blood. Sometimes the blood oxygen pressure is also measured, and possibly several other parameters. Blood may also be tested for microbiology, to determine the presence of bacteria or viruses.
Before the blood test the patient should not take any liquids or food for 12-15 hours, and is only allowed to drink water or lightly sweetened tea. It is best to report for the examination in the morning, after a good night’s sleep. The patient should be well rested, and several hours before the examination he or she should not perform strenuous exercise, because of the possibility of falsification of the results. Unless instructed otherwise by the attending physician, the patient should take all usual medications. For some blood analyses it may be necessary to follow a suitable diet for a few days.
In a single venous blood draw, the vein of the upper limb is usually punctured at the elbow bend; less commonly, blood is drawn from the back of the hand or foot. The patient is asked to place the arm straight in the elbow joint, with the palm facing upwards. The person taking the blood puts a tourniquet on the hand above the venipuncture site. In order to better expose the vein, the patient is often advised to clench his/her hand into a fist. In the place of the planned puncture, the skin is disinfected, e.g. with ethyl alcohol solution, and then the vein is immobilized by pulling the skin tight. The needle is usually attached to a syringe and blood is drawn by pulling the syringe plunger. It is also possible to draw blood using only the needle, in which case the blood that leaks from the other side of the needle is collected in a test tube. When enough blood has been drawn, the examiner presses on the puncture site with a cotton swab and removes the needle from the vein. It is recommended that the patient presses on the bleeding site with a cotton swab for a few minutes to stop the bleeding more quickly.
Capillary blood is usually drawn from an earlobe or fingertip. The site from which the blood is to be drawn is punctured and then gently pressed to constrict the skin. The site is then wiped with a disinfectant solution, and after this solution evaporates, the prepared site is punctured to a depth of about 3 millimeters. The examiner removes the first drops with a gauze pad, and then collects the freely flowing blood with a micropipette or appropriate capillary.
Arterial blood collection is most often done from the radial or femoral artery. The puncture site is thoroughly disinfected before blood is drawn. Sometimes, before the artery is punctured, the examiner anesthetizes the area from which the blood will be drawn and then gently cuts the skin over the artery.
Indications and use
Due to the wide variety of uses for blood tests, the type and extent to which they are performed are determined by the physician. Blood tests are recommended in particular to establish the diagnosis of the disorder from which the patient suffers, to monitor the progress of treatment, as well as the prognosis of the disease. In addition, blood tests should be performed regularly for preventive purposes:
mandatory for all occupational workers – periodic blood tests to assess health,
screening tests – for example, examination of the concentration of total cholesterol, cholesterol of individual lipoprotein fractions and triglycerides to determine the risk of atherosclerosis of the vessels.
There are no absolute contraindications to the blood test. However, relative contraindications include severe coagulation disorders, which may result from the use of anticoagulants.
Complications and side effects
The blood test is not likely to be followed by serious complications. However, minor bruising or hematomas at the injection site are quite common.
Interpretation of blood test results
The normal blood test results for each component should be:
- red blood cells (RBC): for women 4.2-5.4 million/mm3, for men 4.5-5.9 million/mm3 – an increase in erythrocyte values above normal may be associated with true redness, heart defects, chronic lung disease, cancer, Cushing’s syndrome, or renal cystic fibrosis; it may also result from steroid treatment, shock, dehydration, burns, and peritonitis; values below normal are most often associated with anemia, conductivity, or sudden blood loss,
- MCV: female: 81-99fl, male: 80-94fl – elevated MCV may be due to vitamin B12 or folic acid deficiency, diseases such as hepatitis or liver failure, alcoholism, chemotherapy, hemolysis or acute hemorrhage; below-normal values are usually associated with iron deficiency anemia, sideroblastic anemia and thalassemia,
- MCH: 27-31pg – elevated values may be associated with spherocytosis, while decreased values are associated with water-electrolyte disturbances and deficient anemia,
- MCHC: 33-37g/dl – elevated values may be associated with spherocytosis or hypertonic dehydration, and decreased values with water-electrolyte disturbances and iron deficiency anemia,
- Haemoglobin: for females 12-16g/100ml, for males 14-18g/100ml – haemoglobin above normal may be indicative of dehydration, primary hyperaemia and secondary hyperaemia, an increase in haemoglobin above normal may also be associated with hypoxia; haemoglobin deficiency is usually due to anaemia or conductivity,
- Hematocrit: for women: 0.40-0.51, for men: 0.40-0.54 – values above normal may indicate purpura vera, tissue hypoxia, heart defects, tumors, and renal cysts, while values below normal may indicate anemia or conductivity,
- White blood cells: from 4500 to 10000/mm3 – leukocytes above normal may indicate stress, pregnancy, appear during childbirth, after a meal and after exercise, in pathological states an increase in leukocytes occurs with acute and chronic inflammatory processes, infections, tumors, severe hemorrhages and proliferative diseases of the hematopoietic system, an increase in leukocytes also occurs with tissue damage, acute liver necrosis, metabolic disorders and myocardial infarction; On the other hand, subnormal values are seen in cases of bone marrow aplasia and hypoplasia, severe bacterial infection, viral infection, collagen diseases and proliferative syndromes such as leukemia or myeloma. The values are below the normal range,
- Granulocytes: 1.8-8.9 x 109/l,
- Neutrophils: 1.5-7.4 × 109/l – Neutrophil counts above normal are indicative of infections, metabolic, haematological and neoplastic diseases, and occur after trauma, in women in the third trimester of pregnancy, and in smokers; lower neutrophil counts occur with fungal, viral, bacterial and protozoan infections,
- Basophilic granulocytes: 0-0.13×109/l – elevated basophil counts are associated with allergic diseases, chronic inflammation of the gastrointestinal tract, chronic leukemia, ulcerative colitis, and hypothyroidism; decreased basophil counts are associated with acute infections, acute rheumatic fever, acute pneumonia, stress, and hyperthyroidism,
- Acid-filtered granulocytes: 0.02-0.67 × 109/l – elevated eosinophils are present in allergic and parasitic diseases, blood disorders, psoriasis, and certain medications; decreased eosinophils are present in infections, dysentery, septicemia, trauma, burns, and excessive physical exertion,
- Lymphocytes: 1.1-3.5×109/l – a lymphocyte count above normal may indicate chronic leukemia, lymphoma, whooping cough, measles, mumps, syphilis, tuberculosis, rubella, and immunologic diseases, while a lymphocyte count below normal occurs during chronic corticosteroid treatment, severe chronic stress, leukemia, and malignant granulomatosis,
- B lymphocytes: 0.06-0.66×109/l – an excess of B lymphocytes occurs during periods of recovery from infectious diseases, in the course of chronic lymphocytic leukemia, in diseases such as multiple myeloma, Waldenstrom’s macroglobulinemia, and DiGeorge syndrome; decreased numbers of B lymphocytes appear in infectious diseases and stressful situations, in acute lymphoblastic leukemia, and in congenital or acquired immunoglobulin deficiency; B lymphocyte deficiency can also be a symptom of diseases such as: uremia, radiation syndrome, shock syndrome, tuberculosis, hypermagnesemia, Hodgkin’s disease, and AIDS,
- T lymphocytes: 0.77-2.68×109/l – T-lymphocyte content above normal may indicate diseases such as multiple myeloma, chronic lymphocytic leukemia, lymphoma, cytomegalovirus, pertussis, infectious mononucleosis, or hepatitis; A below-normal lymphocyte count, also referred to as lymphopenia, occurs with immunodeficiency, which is associated with diseases such as AIDS, pancytopenia, and kidney failure; the lymphocyte count also declines with circulatory failure; T-lymphocyte deficiency can also be associated with congenital T-lymphocyte deficiencies, as seen in DiGeorge syndrome, Nezelof syndrome and Wiskott-Aldeich syndrome; reduced T-lymphocyte counts are also seen with long-term corticosteroid treatment,
- Monocytes: 0.21-0.92×109/l – their elevated blood levels may indicate tuberculosis, syphilis, endocarditis, infectious mononucleosis, cancer, and protozoan infection, while decreased blood levels indicate infection, and are also found with certain medications,
- Platelets: 140000-450000/mm3 – thrombocyte content above normal occurs with chronic myeloproliferative syndrome, infection, cancer, recovery from hemorrhage and hemolysis; below-normal thrombocyte count may be indicative of plastic anemia, lymphoma, acute myelogenous leukemia, bone marrow fibrosis, megaloblastic and iron deficiency anemia, viral infections, renal failure, and also occurs with ionizing radiation and myelosuppressive drugs.
Plasma test results show the levels of hormones, enzymes, proteins, electrolytes and trace elements in the human body. With their help it is possible to determine the clinical condition of specific organs, glands and systems. It is also possible to determine the state of hydration, nutrition, as well as to determine the progress of a disease.
For some components of plasma, the norm for blood tests is:
- glucose: 70-100mg/dl (3.9-5.6mmol/l) – glucose concentration increases in insulin-dependent diabetes mellitus type 1 and insulin-dependent diabetes mellitus type 2, in gestational diabetes mellitus, in pituitary and adrenal disorders, in Cushing’s syndrome, or in pancreatic diseases, among others; Decreases in glucose levels occur with insulin overdose or failure to eat a meal after the hormone dose, overdose of oral antidiabetic drugs, pituitary or adrenal insufficiency, alcoholism, or toxic liver damage, among other conditions,
- Total cholesterol: 140-200mg/dl (3.6-5.2mmol/l) – total cholesterol levels increase in familial hypercholesterolemia, combined familial hyperlipidemia, common hypercholesterolemia, extrahepatic jaundice and in liver diseases such as: primary biliary cirrhosis, benign hepatitis, von Giercki disease, as well as in chronic renal failure, nephrotic syndrome, chronic pancreatitis, diabetes mellitus, hypothyroidism, obesity, pregnancy, and during the use of certain medications; a decrease in cholesterol occurs with certain liver diseases, including advanced cirrhosis, subacute hepatic necrosis, toxic liver damage, as well as starvation, sepsis, anemia, and hyperthyroidism,
- triglycerides: 60-165mg/dl (0.55-2.0mmol/l) – increased plasma triglycerides may be associated with complex hyperlipidemia, familial dysbetalipoproteinemia, excessive alcohol consumption, diabetes mellitus, hypothyroidism and renal insufficiency, pancreatitis, nephrotic syndrome, taking oral contraceptives, gout, and pregnancy; while decreased levels appear in mentally ill and chronically hospitalized patients,
- uric acid: 0.15-0.45mmol/l (2.5-8.0mg/dl) – increased levels may be associated with gout, psoriasis, cancer, tissue hypoxia, excessive intake of purines in the diet; decreased levels may result from inhibited tubular reabsorption ,
- urea: 2.5-6.4 mmol/l (15-39mg/dl) – an increase in urea concentration may be associated with a diet high in proteins and excessive catabolism of body proteins, which occurs in fever and sepsis; excessive urea concentration also occurs in renal insufficiency and extra-renal insufficiency, while a decrease in urea concentration has no significant clinical significance,
- total protein: 60-80mg/dl – increased total protein may be associated with excessive fluid loss – vomiting, diarrhea; whereas decreased protein often results from conductivity or intensive loss or impaired synthesis in the liver; decreased total protein also accompanies kidney disease, gastrointestinal disease and burns,
- albumin: 3.5-5.0g/dl – an increase in plasma albumin concentration is led by dehydration, while a decrease is observed with decreased albumin synthesis, malabsorption, malnutrition, burns, bleeding, sepsis, conductivity, cancer, nephrotic syndrome, liver disease, and gastrointestinal disease,
- total bilirubin: 0.3-1.2mg/dl – an increase in total bilirubin is observed during pregnancy and in newborns, as well as in pathological conditions such as jaundice, biliary cirrhosis, bile duct cancer, sclerosing cholangitis, Gilbert’s disease, alcoholic liver disease, or in toadstool poisoning ; In addition, bilirubin levels are elevated when many drugs are taken that damage the liver parenchyma; below-normal bilirubin levels are of little clinical value,
- creatinine: 62-124mmol/l (0.7-1.4mg/dl) – an increase in creatinine concentration occurs in gigantism, acromegaly and after physical exertion, whereas a decrease in concentration is usually associated with kidney failure, intoxication with organic and inorganic compounds, and the use of drugs whose side effects are detrimental to the kidneys; a decrease in plasma creatinine may also occur with starvation.