In this next quick reference guide, I want to review the CBC (complete blood count). This is one of the most common routine blood tests that we order in primary care. It is a collection of lab values that helps us to evaluate your blood cells. There are many components that the CBC looks at, and I would like to discuss the 4 most important with you below:

WBC: White Blood Cell

Hgb/Hct: Hemoglobin and Hematocrit

MCV: Mean Corpuscular Volume

Plt: Platelet

The lab ranges I have listed below are only averages. Some laboratories may use different ranges based on the assays they use.

WBC: White Blood Cell

Range: 4,000-11,000 per microliter

White blood cells are a major part of your body’s immune system. They are a good marker to use to evaluate your immune system’s functional status.

Leukocytosis

An elevated white blood cell count usually indicates that your body is fighting some kind of infection or is responding to a significant stressor. Sometimes, taking steroids can artificially increase your white blood cell count even when you are not fighting any infection. However, a persistent and large increase in white blood cells may be the first sign of leukemia. A common follow-up blood test to confirm this is a peripheral smear. A smear is a test in which a blood sample is inspected by a pathologist under a microscope. This can be helpful to determine if any abnormal looking lymphoma cells are present in the blood.

Leukopenia

A low count can come from infection as well. Sometimes certain infections will consume white blood cells rapidly causing a sudden drop in the count. This is ok as long as other parts of the immune system take over to fight the infection. Another common cause of low white blood cell count is chemotherapy. The WBC level must be closely monitored in patients receiving chemotherapy. A significant drop can indicate that your body is immunocompromised.

Hgb/Hct: Hemoglobin and Hematocrit

Hgb range: 13-17 g/dL

Hct range: 36%-50%

Hemoglobin is the protein that carries oxygen within your red blood cells. As your red blood cells travel throughout your arteries, the oxygen is unloaded from the hemoglobin and delivered to all tissues of the body. The hemoglobin level is a direct measurement of the hemoglobin in your blood sample, and the hematocrit is the percentage of red blood cells in your blood. We use both levels to evaluate your blood for anemia and other disorders.

Generally, you can multiply your hemoglobin count by 3 to get your hematocrit.

Polycythemia

Polycythemia is the condition of having an elevated hemoglobin and hematocrit level. This generally comes from either of 3 causes. Polycythemia vera, a rare genetic disorder, causes over production of red blood cells in the bone marrow with no checks or balances to turn the production off. Polycythemia vera is treated with phlebotomy or blood-letting.

The second cause can come from dehydration. As I discuss in my article, No Test Is Perfect, some tests can have false positives. Dehydration is one condition that can temporarily and falsely elevate your Hgb/Hct.

The third, and much more common cause of polycythemia, is chronic hypoxia, or low oxygen levels. When your body senses low oxygen levels, your kidneys increase the production of a hormone called erythropoeitin. Erythropoeitin then stimulates your bone marrow to increase your red blood cell production. Your body assumes that if you are not delivering enough oxygen to your cells, then you should increase your oxygen delivery capacity by producing more red blood cells. Chronic hypoxia can come from chronic lung disease or undiagnosed sleep apnea.

Anemia

A low hemoglobin and hematocrit means that you are anemic. Anemia can come from either not producing enough red blood cells, or can come from losing too many red blood cells. To evaluate the cause of anemia, we use the mean corpuscular volume, or MCV for short. See below:

MCV: Mean Corpuscular Volume

Range 80-100 cubic microns

The mean corpuscular volume is the actual size of the red blood cells. The size of your RBCs helps us to determine why you have anemia.

Microcytic anemia

Having small red blood cells <80 cubic microns indicate is called microcytic anemia. It can indicate your anemia is coming from iron deficiency. As I mentioned above, this can come from not getting enough iron in the diet or it can come from acute or chronic blood loss.

The most common cause of chronic blood loss is occult bleeding in the gastrointestinal tract. Standard work-up for iron deficiency anemia is to perform an upper and lower endoscopy of the GI tract to look for a source of bleeding.

The second most common cause of a microcytic anemia is menorrhagia, or heavy periods. Many women with heavy periods will require iron supplementation in order to prevent the development of iron deficiency anemia.

Thalassemia is a rare inherited blood disorder that can also cause microcytic anemia. Patients with thalassemia have a chronic anemia that is usually asymptomatic. A test called a hemoglobin electrophoresis can tell us whether or not you have thalassemia.

Macrocytic anemia

Macrocytic anemia is the presence of large red blood cells >100 cubic microns. This commonly comes from vitamin B12 deficiency, folate deficiency, or can come from excessive alcohol use. Rarely, this can be caused by a bone marrow disorder, but the previous 3 reasons are much more common.

Plt: Platelet count

Range 150,000-450,000 per microliter

Platelets are the tiny blood cell fragments that stop bleeding. If you start bleeding, then your platelets clump together to form blood clots to keep your body from losing too much blood.

Thrombocytosis

Thrombocytosis is a condition in which your body has too many platelets. The most common cause of platelet level elevation above 450,000 is not dangerous. It’s usually elevated temporarily due to acute inflammation in the body. Cells and proteins that temporarily elevate in response to inflammation are called acute phase reactants. Other examples of acute phase reactants include ferritin, C-reactive protein, and erythrocyte sedimentation rate.

The other cause of platelet elevation is more rare. It is called essential thrombocytosis and this is cause by a genetic mutation in the platelet producing cells of your bone marrow. This can be controlled with medication.

Thrombocytopenia

Thrombocytopenia is the name of the condition when your blood stream is platelet deficient. The severity of thrombocytopenia depends on your platelet level. Most patients won’t notice any ill effects while the platelet level remains above 50,000. If the platelet level drops below 50,000, then you should generally avoid invasive procedures, including operations. Once the platelet level drops below 10,000, then patients can experience spontaneous bleeding from anywhere without provocation.

Common causes of thrombocytopenia include alcohol abuse, liver cirrhosis, and an enlarged spleen. Rare causes of thrombocytopenia include an autoimmune condition called idiopathic thrombocytopenic purpura (ITP), viral illnesses like HIV and hepatitis, and certain medications (especially chemotherapy).

The Cures Act gives patients immediate access to their lab results via their electronic medical record. While this does give patients more control over their health information, it can cause problems. Trying to interpret lab results without the help of a healthcare professional can lead patients to make the wrong conclusions. This can cause unnecessary anxiety, panicked calls to the doctor, and perhaps, patients may take the wrong course of action before speaking with a doctor.

I want all of my Wise Patients to have access to their results. My hope is that with these quick reference guides, you will have a basic idea of what these tests are and what the results are looking for.

Interested in reading more quick reference guides? This link will take you to all of the Quick Reference Guides published so far.