You often hear the term when you are in your doctor’s office…CBC—a complete blood count. But you probably don’t know exactly what it measures and what the results say about your health.

When should you have one? A CBC test should be part of your yearly wellness visit. It is especially important when you are having symptoms such as fatigue, unintentional weight loss, fever or signs of infection, generalized muscle weakness or easy bruising or bleeding. The results can provide clues about a range of conditions—benign or malignant. A CBC also can measure progress from medical treatments such as chemotherapy, follow-up on medications that can affect blood counts (for example, medications for autoimmune conditions and certain antibiotics) and monitor existing conditions.

If you have had a CBC recently…or will be getting one in the future…here’s what the results might mean…

Basics of blood: Your blood is made up of plasma—a mix of water, salts and proteins—and cells. The latter can be measured by a CBC. The results give your doctor a blueprint of your health and help to catch serious diseases early. Blood components measured by CBC…

Red blood cells (RBCs) deliver oxygen from your lungs to your tissues and organs. Normal range: 4 million to 5.2 million cells/microliter (mcL) for women…4.5 million cells/mcL to 6 million cells/mcL for men.

Hemoglobin is an iron-rich protein in red blood cells. Normal range: 12 grams per deciliter (g/dL) to 16 g/dL for women…13.5 to 17.5 g/dL for men.

Hematocrit shows the percentage of red blood cells in your total blood. Normal range: 36% to 46% for women…41% to 53% for men.

Mean corpuscular volume (MCV) measures the average size of your red blood cells. Normal range: 80 to 100 femtoliters.

Mean corpuscular hemoglobin (MCH) measures the average amount of hemoglobin in a single red blood cell. Normal range: 26 to 34 picograms per cell.

Mean corpuscular hemoglobin concentration (MCHC) shows the hemoglobin content in relation to its volume in each red blood cell. Normal range: 32 g/dL to 36 g/dL.

White blood cells (WBCs) are your primary infection fighters and first responders to any acute or chronic inflammation and stress. Normal range: 3,730 to 10,800 per cubic millimeter (mm3).

Platelets are blood cell fragments that help your blood to clot and stop bleeding. Normal range: 150,000 to 450,000 million cells/mcL.

Sometimes your doctor will order a CBC with differential. This will also measure the percentage of each of the five types of white blood cells and look for any immature forms that should not be present in the peripheral blood.…

Neutrophils, the most numerous subset of white blood cells, are your first line of defense against invaders. When bacteria or viruses enter the body, neutrophils are one of the first immune cells to respond. Normal range: 50% to 70%.

Monocytes fight off microbes including bacteria to fend off infection. They are the key players of the innate immune system. Normal range: 3.5% to 9%.

Lymphocytes are another subset of immune cells. There are two groups— T cells directly attack and kill infected cells and tumor cells…B cells create antibodies to fight bacteria, viruses and other invaders. Normal range: 18% to 42%.

Basophils go into action when you’re under threat. They play an active role in the development of allergic reactions and prevention of blood clots. Example: They release histamine during an allergic reaction as part of your body’s immune response. Normal range: 0% to 1%.

Eosinophils combat multicellular parasites and certain infections. Along with basophils, they also control mechanisms associated with allergic reactions. Normal range: 1% to 3%.

How your doctor deciphers the results: The reasons for a low or high number of any blood component are vast, and CBC results are one factor that your doctor will consider when assessing your health. But there are medical conditions related to certain blood measures…

High RBCs, hemoglobin and hematocrit may indicate severe dehydration…heart or lung diseases…or be a side effect of taking certain medications (for example, testosterone). These parameters also could be elevated because of specific cancers (for example, kidney or liver diseases) or increased due to malfunction of the bone marrow itself.

Low RBCs, hemoglobin and hematocrit may show anemia due to acquired or inherited reasons. Examples: Those parameters are low in sickle cell disease (low hemoglobin and usually normal MCV) or thalassemia (low hemoglobin and low MCV). Acquired conditions could include solid or blood cancers such as leukemias, lymphomas or multiple myeloma or various cancer treatments…chronic inflammatory conditions such as ulcerative colitis or rheumatoid arthritis…problems with the thyroid gland, liver or kidneys and/or diet deficiencies. RBCs, hemoglobin and hematocrit can be low due to increased cell destruction by the body—patients feel fatigued, short of breath and their skin can turn yellow.

Low platelet count may suggest a bleeding disorder or a transient or permanent condition associated with autoimmune diseases, infections, medication side effects, malignancies or liver disorders.

High platelet count may be the body’s way of expressing a blood-clotting problem due to bone marrow malfunction or be part of a reactive process such as iron deficiency or active infection. Your doctor might order specific DNA tests to evaluate your predisposition to increased clotting, early heart attacks or strokes. If you are taking a blood thinner, CBC and platelet count, in particular, become a part of your routine safety drug monitoring along with your regular clotting studies (such as INR and anti-factor Xa).

Low WBCs may be evidence of a lowered ability to fight infection…alcohol abuse and liver damage…some ­autoimmune diseases…bone marrow issues…or it could be a side effect of medications such as antibiotics and ­chemotherapy. Low total WBCs also can be a norm in certain populations (African Americans and Mediterranean-descent groups are prone to this) and, in these cases, does not predispose patients to higher infection risks.

High WBCs may imply an acute or chronic infection…some autoimmune diseases or other cause of inflammation…blood cancers or other bone marrow diseases…severe emotional or physical stress…or tissue damage…or it can be a side effect of certain medications such as corticosteroids or smoking.

Putting your results in perspective: CBCs and other blood tests complement your medical history and physical exam. Your doctor will look for trends. Examples: If your WBCs are just below 3,700/mm3 and your medical history shows it has been at that level for 10 years and you have no symptoms, it’s likely that is the number you’ve been living with and isn’t cause for concern. If your hemoglobin is slightly lower than the normal range but not causing shortness of breath or fatigue, it could just be low at that moment. But if a number is drastically off or moving in the wrong direction—say your platelets today are 10,000 million cells/mcL of blood instead of the 150,000 from one year ago—your doctor will order follow-up tests.

Tests Beyond the CBC

There are other tests that will help your doctor get a more complete picture of your health…

Comprehensive metabolic panel measures levels of 14 naturally occurring chemicals in blood plasma, including glucose, calcium, sodium, potassium, carbon dioxide, chloride, albumin, total protein, ­bilirubin, BUN (blood urea nitrogen) and creatinine. Abnormal levels can be a sign of a problem involving key organs, such as the heart and lungs, liver or kidneys or, in the case of ­glucose, diabetes or prediabetes.

Lipoprotein panel measures cholesterol (total cholesterol, HDL, LDL and VLDL/very low density lipoprotein) and triglycerides in your blood. A relatively new measure is non-HDL cholesterol—total cholesterol minus good HDL. Some experts believe that this number is a simple way to assess heart disease risk.

If results of metabolic and lipoprotein panels are borderline or abnormal, consider lifestyle changes to help improve your numbers.

Testing for nutrient deficiencies. A CBC can indicate deficiencies in nutrients such as iron, vitamins B-12 and folic acid, and minerals copper and zinc. This is particularly important for patients who have had weight-reduction surgeries or other procedures on the stomach or bowel.

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