What You Need to Know About Blood Testing

What You Need to Know About Blood Testing

Blood testing is an important tool in medical diagnosis and management. It is used to detect disease, measure a patient’s general health, or monitor the effects of treatment.


Most blood tests are very simple and require no special preparation. For certain tests, your doctor may advise you to fast for several hours before a test. It is important to drink plenty of fluids and to follow your doctor's instructions for preparing for a test.


A sample of blood is taken either from a vein in the arm or a fingertip, depending on the nature of the test. A lab technician performs the test, usually within 20 minutes. The results are sent to the requesting doctor or clinic for assessment.

Types ofBlood Tests

  • Complete Blood Count (CBC): This is a commonly ordered test to measure the general health of the patient. It looks at the number and types of cells present, the hemoglobin concentration, and the hematocrit.
  • Comprehensive Metabolic Panel (CMP): This test looks at organ function such as the kidneys, liver, and pancreas. It also looks at electrolyte and protein levels.
  • Lipid Profile: This test looks at cholesterol and triglyceride levels.
  • Thyroid Function Tests: These tests measure levels of hormones secreted by the thyroid gland.
  • Blood Typing: This test is used to determine a person’s blood type. Knowing the blood type can be critical during a medical emergency.
  • Diabetes Monitoring: This test measures the level of glucose in the blood. It is used to detect diabetes or to monitor glucose levels in people with diabetes.
  • HIV Test: This test looks for antibodies to the human immunodeficiency virus, which can lead to acquired immunodeficiency syndrome (AIDS).
  • Vitamin Levels: Various vitamins and minerals can be measured with a blood test.

Risks and Side Effects

Blood tests are usually very safe, but there can be some risks and side effects. The most common complication is pain, bruising, or swelling at the draw site due to the needle puncture. People with bleeding disorders or those taking anticoagulant medications are at higher risk of bleeding.

Why Are Blood Tests Done?

Your doctor may order blood tests for a variety of reasons including: diagnosis of an illness or condition, monitoring the effectiveness of a treatment, checking for side effects of a medication, or to get a baseline measurement before starting a new medication or therapy.

When Are Blood Tests Done?

Blood tests may be done as part of a routine checkup or when a person has certain symptoms, such as fatigue, unexplained weight loss, or fever. Tests may also be done if a doctor suspects a condition, such as anemia or diabetes. Your doctor may also order tests based on results from a physical examination or other diagnostic tests.