Blood Tests

General Description

Blood tests are a useful tool to assess a patient’s health status and detect abnormalities that may indicate the presence of a disease or dysfunction in the body’s organs. They are also an important procedure to evaluate the effectiveness of treatments for managing illnesses.

Blood tests are typically tailored to the specific needs of each situation, meaning not all aspects are always studied. A complete blood test usually includes:

• Complete Blood Count (CBC): This examines various components of the blood that influence many aspects of the body's function, making it the most common test, particularly during routine check-ups.
  • Red Blood Cell Count: Measures the number of red blood cells responsible for transporting oxygen from the lungs to the rest of the body.
  • White Blood Cell Count: Determines the number of white blood cells (basophils, eosinophils, lymphocytes, neutrophils, monocytes), which are part of the immune system.
  • Platelet Count: Counts the number of platelets, which help the blood clot and stop bleeding.
  • Hemoglobin Concentration: Indicates the amount of hemoglobin (iron-rich proteins) in the red blood cells.
    • Mean Corpuscular Hemoglobin (MCH): Average amount of hemoglobin in a single red blood cell.
    • Mean Corpuscular Hemoglobin Concentration (MCHC): Measures how concentrated hemoglobin is in red blood cells, as well as their size and volume.
• Hematocrit Levels: Refers to the amount and size of red blood cells, indicating the proportion of blood composed of red blood cells.
• Red Cell Distribution Width (RDW): Determines the production of blood cells.
• Mean Corpuscular Volume (MCV): Determines the average size of red blood cells.
• C-Reactive Protein (CRP) Test: Measures the levels of this protein in the blood. High sensitivity CRP tests detect even minimal variations.
• Biochemistry or Metabolic Profile: Analyzes various elements that make up plasma, the liquid portion of the blood. It is used to measure calcium, electrolytes, glucose, and to assess kidney function, as kidneys filter and purify the blood.
• Enzymes: These substances help control chemical reactions in the body. The purpose of the test is to identify the presence or excess of enzymes or proteins released into the blood when there is an illness or disruption in the body.
• Lipoproteins: A lipid profile studies levels of triglycerides and LDL cholesterol (known as "bad" cholesterol because it clogs arteries) and HDL cholesterol (referred to as "good" cholesterol because it helps reduce accumulated LDL).
• Coagulation: Focuses on the study of proteins that help the blood clot to prevent excessive bleeding.

When is it indicated?

Blood tests are indicated to diagnose various diseases, check the functioning of different organs (liver, kidneys, thyroid, heart), monitor the progress of chronic conditions, or evaluate whether the patient is responding appropriately to specific treatments.

• Complete Blood Count:
  • Red Blood Cell Count: Abnormal levels may indicate anemia, bleeding, leukemia, malnutrition, or dehydration.
  • White Blood Cell Count: Excess or deficiency in white blood cells suggests infection, immune system disorders, or hematologic cancers like leukemia, lymphoma, and multiple myeloma.
  • Platelet Count: An improper number of platelets may indicate coagulation disorders like antiphospholipid syndrome or disseminated intravascular coagulation, or bleeding disorders such as hemophilia.
  • Hemoglobin Concentration: Low levels can indicate anemia, liver disease, or thalassemia. High levels are associated with polycythemia vera or lung disease.
  • Hematocrit Levels: Fewer red blood cells than expected could signal anemia. More may indicate dehydration.
  • Mean Corpuscular Volume (MCV): Large red blood cells may be due to folic acid deficiency, hypothyroidism, liver disease, or excessive alcohol use. Smaller red blood cells could be caused by iron-deficiency anemia, thalassemia, or chronic infections.
  • C-Reactive Protein (CRP) Test: Elevated levels suggest infection or chronic inflammatory diseases. High-sensitivity CRP tests are commonly used to determine the risk of heart diseaseHeart DiseaseHeart Disease or recurrent heart attacks.
  • Biochemistry: Provides information on the function of the kidneys, heart, and liver, and helps diagnose conditions like diabetes or dyslipidemiaDyslipidemiaDyslipidemia (high cholesterol or triglycerides).
    • Enzymes: Useful for studying heart or liver function and detecting conditions like myocardial infarction or liver damage.
    • Gamma-Glutamyl Transferase (GGT): Evaluates liver, gallbladder, and bile duct function.
    • Glutamate-Pyruvate Transaminase (GPT) or Alanine Aminotransferase (ALT): Provides insights into drug or alcohol abuse, liver injury, or muscle disorders.
    • Aspartate Aminotransferase (AST or GOT): Helps detect myocardial infarction, pancreatitis, or liver and heart damage.
    • Lactate Dehydrogenase Isoenzymes (LDH): Tests for tissue damage.
    • Lipoproteins: Typically used to diagnose atherosclerosis or cardiovascular disease.
    • Coagulation: Studies the risk of clot formation or excessive bleeding. Often used to monitor patients on anticoagulant therapy.

How is it performed?

A blood test involves taking a serum sample, usually from a vein in the arm. Depending on the tests to be done, the amount of blood drawn may vary. A complete test typically requires three 10-milliliter tubes.

These tubes are labeled with the patient's name, sample code, and extraction date, and are sent to the laboratory. There, the blood is processed to prepare it for the required test, often undergoing centrifugation to separate the cells. The yellow serum is at the top, used for most tests, while the cells settle at the bottom of the tube.

Laboratories now have technology that allows for multiple tests to be conducted simultaneously, providing organized reports of all requested analyses.

Risks

A blood test is generally not risky for health.

Some patients may feel slight dizziness, especially if a large amount of blood is drawn, but this typically resolves quickly if they lie down with their feet elevated. A bruise may form at the puncture site.

What to expect from a blood test

Blood extraction is performed with the patient seated and the arm extended, so it’s advisable to wear sleeveless clothing or easily removable garments. Those who are prone to fainting during blood draws should inform the staff so they can lie down on a bed during and after the procedure.

After disinfecting the area, typically the inner elbow, a tourniquet is placed to facilitate the blood draw. A needle is inserted into the vein (at which point a slight pinch is felt, which is not very painful), the tourniquet is removed, and the necessary tubes are filled using a syringe.

To reduce bruising, a bandage is applied to the puncture site, which should be pressed for a few minutes.

Once the process is complete, the patient should drink plenty of fluids to help replenish the blood that was taken.

Some tests take longer than others in the laboratory, but results are usually available within a week.

Specialties that request blood tests

Blood tests are ordered in all medical specialties as an initial step to assess a patient's health or diagnose diseases.