Blood Laboratory Tests
Full Blood Examination
Full blood examination also known as complete blood count or cell blood count is a lab study that counts the cells of the peripheral blood: Red Blood Cells (erythrocytes), White Blood Cells (leukocytes), Platelets (thrombocytes). The number of cells is given in absolute numbers per liter. Regarding red blood, the test provides the physician information on the amount of blood hemoglobin, hematocrit, mean corpuscular volume, mean corpuscular hemoglobin, mean corpuscular hemoglobin concentration, and red blood cell distribution width. Regarding white blood, the test gives information on differentials: neutrophil granulocytes (with attention to their types of maturity), lymphocytes, monocytes, eosinophil granulocytes, basophil granulocytes. As for the platelets, mean platelet volume is given. The full blood examination is compulsory in most clinical situations, it shows essential information on possible anemia, infections, blood disorders and thrombocytopenia.
Reticulocyte count test is a part of the full blood examination. In this test, the number of reticulocytes (young erythrocytes) is counted. Thus, the test estimates how erythropoiesis intensive is. This is an important tool to appreciate anemia treatment progress.
Erythrocyte sedimentation rate is the speed of Red Blood Cells falling down in a tube, measured in mm/h. The test is useful in appreciating inflammation.
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Coagulation profile includes prothrombin time, activated partial thromboplastin time, fibrinogen and thrombin clotting time. Prothrombin time measures the ‘extrinsic’ part of the coagulation, with this lab oral anticoagulants (like Coumadin) are controlled. Activated partial thromboplastin time is used to control efficacy of heparin treatment. Biologically, activated partial thromboplastin time studies the ‘intrinsic’ coagulation pathway. Fibrinogen is a protein essential for clotting. Thrombin clotting time is the time clotting takes in the presence of an anticoagulant. Thrombin clotting time is used to check fibrinolysis. Coagulation profile is used to manage common bleeding disorders, severe infections, liver failure, disseminated intravascular coagulation and therapeutic anticoagulation.
D-Dimer is a product of clot breakdown. The test shows body clotting/fibrinolysis activity. Blood film malaria is a microscopic investigation of blood aiming at detecting Malaria parasites. The idea of the test is to take thick films of blood, which allows to screen larger volumes of blood with a greater chance to make a diagnosis. With the recent advance of polymerase chain reaction, the blood film test became a cheap screening method.
Peripheral blood smear is a thin layer of blood on a microscope glass. The smear is specially stained so that blood cells are studied microscopically. This is the basis for complete blood count.
Infectious Mononucleosis test also known as the Monospot Test is agglutination of the horse Red Blood Cells by patient’s serum antibodies. The human heterophile antibodies are responses to the Epstein Barr virus.
Liver function test consists of bilirubin (both direct and indirect), albumin, prothrombin time and liver transaminases (AST and ALT, alkaline phosphatase, gamma glutamyl transpeptidase), lactate dehydrogenase. The tests appreciate detoxification (bilirubin), synthesis (albumin, prothrombin time), excretion (bilirubin), cell damage (bilirubin, transaminases, lactate dehydrogenase, gamma glutamyl transpeptidase), cholestasis (alkaline phosphatase), suggests history of alcohol abuse (gamma glutamyl transpeptidase).
Kidney function test consists of urea, creatinine, glomerular filtration rate and electrolytes. These chemicals must be excreted by the kidneys (urea, creatinine) with a sufficient rate (glomerular filtration rate), while salts must be supported at a physiological balance (sodium, potassium, chlorides, bicarbonate).
Cardiac markers are normal components of cardiac cells. Should the myocardium be damaged, their level rises promptly (troponins, myoglobin) or with some delay (creatine kinase –MB, lactate dehydrogenase cardiac type, AST). The stretch of cardiac chambers also leads to release of some chemicals (pro-brain natriuretic peptide) indicating heart failure.
Therapeutic drugs level is an essential part of the patient’s body when prescribing medicines with high toxicity potential. Digoxin is used in heart failure, intoxication with Digoxin causes arrhythmias. Gentamicin is toxic to ears and kidneys. Vancomycin may cause injuries to the kidneys. Paracetamol may damage the liver badly.
Alcohol level measures the amount of ethanol in blood. The test is used in medical and legal situations to measure alcohol intoxication in an objective form. Blood ethanol is graded as absent, positive (varying levels of intoxication) and lethal.
Serum bilirubin level appreciates how well the liver detoxification unconjugated (indirect) bilirubin through bounding it with glucuronic acid to produce safe type of bilirubin, conjugated (direct). The test not only checks for liver function and hepatocyte integrity, but also differentiates different types of jaundice.
Uric acid test determines the level of uric acid in the blood. Uric acid is the by-product of decay rich in purine food products (meat, liver, wine, beer, beans). The elevated level of uric acids suggests gout.
Electrolyte tests. Potassium: low level due to excessive diuresis, high level suggests kidney failure, both low and high levels affect cardiac function. Sodium: low levels suggest hypervolemia (as in congestive heart failure), high levels indicate hypovolemia (water loss in vomiting, water starvation). Chloride: high levels suggested in cystic fibrosis, diarrhea, and low levels in excessive water loss. Bicarbonate: high levels suggest alkalosis (respiratory in tachypnea or metabolic in alkaline medicines overdose), low levels indicate acidosis (respiratory in bradipnea, metabolic in shock, and critical conditions).
Calcium, Magnesium, Phosphorus. Calcium is essential for cardiac function and bone metabolism. Low calcium indicates parathyroid malfunction or vitamin D deficiency, and in critical conditions (burns, pancreatitis). High calcium may indicate malignancies, renal failure, endocrine disorders. Magnesium is a natural antagonist of calcium. Low magnesium if found in excessive diuresis and infusions. High magnesium is seen in acidosis and hemolysis. Phosphorus level decreases in diuresis, alcoholism and redistribution, and elevates in trauma, renal failure, and skeletal disorders.
Alkaline phosphatase is an enzyme that removes phosphate groups from molecules. The enzyme is elevated in cholestasis. Bones also contain alkaline phosphatase, the fact that needs to be accounted for in the differential diagnosis.
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Beta-HCG Test is a pregnancy test. Human chorionic gonadotropin is an enzyme that the developing embryo produces very soon after conception. Gonadotropin is excreted with the urine. Urine test strips are an easy, fast and reliable test to detect pregnancy in the early phase.
Troponin test is a marker of cardiac damage. Troponins are essential molecules that provide contractility of the cardiac muscles. In cardiac insult, such as necrosis of the cardiomyocytes during the myocardial infarction, the cells disrupt and release troponins into the bloodstream. The troponin levels elevated as soon as a couple of hours after the onset of heart attack. This test is very useful in confirming myocardial infarction, especially when other tests (complaints, electrocardiogram, echocardiography) are doubtful.
Blood grouping tests state what group this blood sample belongs to. There are many approaches to blood groups. Traditionally, the ABO system is used worldwide most commonly. It is assumed that Red Blood Cells have antigens on their surface, called A or B. When the RBC has no antigens (neither A nor B), the group is I(O), when only type A it is referred to group II(A), B corresponds to group III(B), and when both A and B are present, this is group IV(AB). Technically, the physicians know which type of antigen is present by using reactions with appropriate antibodies. The second most common grouping test is the Rh-test. All RBCs are divided into those that have an Rh, called Rh(+) positive, and those that don’t, called Rh(-) negative.
Cross-matching tests are essential in transfusion medicine. In classical cross-matching, a drip of packed RBCs is placed. The patient’s serum is taken and mixed with the drip at a 10:1 ratio. The mixture is placed in warmth and exposed. Finally, the sample is microscopically checked for compatibility – no agglutination must be present. Only after the cross-matching test is complete, transfusion may start.
Direct antiglobulin test, also known as Coombs test is an immune reaction based on antigen-antibody adhesion. The kit for a given antibody (human IgG or IgM of a certain disorder) is added to the patient’s blood. The immune set is an antibody attached to an animal’s RBC. As a result, the immune reaction will be visible and easy to read. The Coombs test is used to diagnose hematological and immune disorders.
Kleihauer test measures how much of fetal hemoglobin transfused from the fetus to the mother. Hemoglobin in the fetus is different from hemoglobin in the adult. Normally, within the first months of life fetal hemoglobin is replaced by adult type. In the Kleihauer test, a blood smear is exposed to acid so that adult hemoglobin is eliminated and only the fetal remains. The test provides information on fetal–maternal hemorrhage.
Antibodies screening test aims at detecting unexpected antibodies to RBCs, especially the non-ABO system: Kidd, Kell, Duffy, P and MNS. These antibodies can be both IgM and IgG. They may cause adverse reactions in transfusion, such as hemolysis.
Body fluid cell count. Body fluids other than blood include cerebrospinal fluid, peritoneal, pleural, pericardial and synovial fluid. All these fluids normally contain electrolytes, cells, and glucose. As in complete blood count, the fluids can be assessed microscopically and their differential accounted. As with blood smears, various cell patterns may indicate certain local conditions (mostly inflammatory).
Urine analysis is a set of tests performed on urine. These include cell count, protein, pH, osmolarity, electrolytes, glucose, ketone bodies, gravity, bacterial cultures. Sometimes, hormones and human chorionic gonadotropin are checked for if indicated.