What is a blood test?

Blood tests refers to a blood sample taken and and tested in a lab to evaluate your health. A complete blood count, or CBC, measures the cells that make up your blood, such as red blood cells, white blood cells and platelets, often detecting disorders such as anemia, infection and leukemia. A blood panel identifies the level of glucose and lipids in your blood and can indicate your risk for chronic disease.

Why is a blood test done?

Your doctor may order a complete blood count, or CBC, to identify an illness or determine the underlying cause of symptoms by looking at the quantity, concentration and shape or size of blood cells. Occasionally, a CBC is ordered during regular check-ups.

CBCs measure the following:

  • White blood cells (WBCs) – White blood cells help fight infections in the body. High or low white blood count levels could indicate different types of infections in your body. Normal range of white blood cells is 4,500 cell/mcL to 10,000 cells/mcL.
  • Red blood cells (RBCs) – Red blood cells carry oxygen through the body and filter carbon dioxide. If the red blood cell count is low, you could have anemia or another condition. The normal range of red blood cells in men is 5 million to 6 million cells/mcL, and for women it is 4 to 5 million cells/mcL.
  • Hemoglobin (Hbg) – Hemoglobin is the oxygen carrying protein in the red blood cells. Men should have 14 to 17 gms/dL, and women should have 12 to 15 gm/dL of hemoglobin in the blood.
  • Hematocrit (Hct) – Hematocrit is the amount of blood in the red blood cells. If you have too little hematocrit, you may not have enough iron in the blood. Normal range for men is typically between 41% to 50% and for women between 36% and 44%.
  • Platelets  Platelets help blood cells clot, the amount and size of platelets in your blood can help determine health issues. A normal range is between 140,000 to 450,000 cells/mcL.

Another blood test you may have done is a blood panel, which will usually include lipid and glucose tests, rather than measuring the specifics of your blood cells. In most cases, your primary care doctor will order a blood panel each year during your annual physical. It is normal to fast before this kind of blood test.

Blood panels check the levels of your:

  • Total cholesterol – Cholesterol is a type of fat found in the blood that can be determined by genetic factors and modified by what you eat, with a direct impact on your health. You need cholesterol to keep your blood cells healthy, but too much can lead to disease in the heart or arteries. Normal level for total cholesterol should be under 200 mg/dL.
  • Low-density lipoprotein (LDL) – "Bad" cholesterol in the blood which can lead to heart or blood vessel disease if too high. Foods that are high in saturated fat, such as processed oils and butter, increase your LDL. Normal LDL level should be less than 100 mg/dL.
  • High-density lipoprotein (HDL) – "Good" cholesterol should indicate a reduced risk of heart disease and can be found in foods like fish and nuts. Normal HDL level should be 60 mg/dL or higher.
  • Triglycerides – Calories from eating that aren't needed right away for energy are turned into triglycerides and stored in the body. Triglycerides can increase your risk of obesity and heart disease. Normal level of triglycerides is less than 150 mg/dL.
  • Hemoglobin (Hbg) A1C – A1C is used to calculate your risk for diabetes. Normal level of A1C is between 4-5.6%. A1C levels of 5.7-6.4% indicate an increased risk of diabetes and may result in a pre-diabetes diagnosis. Those with diabetes typically have at least 6.5% A1C and strive to keep their levels below 7% to prevent further health complications.

What to expect during a blood test

Blood tests require a draw from a vein in your arm or hand. You will likely have a band tourniquet to increase blood flow to an accessible vein. The needle will be attached to a thin tube and small vile that will fill once inserted into the vein. Occasionally, a minor blood test can be collected from a finger prick.

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