White blood cells, platelets, and result interpretation

White blood cell tests

The white blood cell tests included in the CBC are the WBC count and a WBC differential. The following sections discuss these tests.

White blood cell count

The WBC count gives an estimate of the total number of leukocytes in circulating blood. The count is performed to help the provider determine whether an infection is present or to aid in the diagnosis of leukemia. It also may be used to follow the course of a disease and indicate if the patient is responding to treatment.

The normal WBC count varies with age. It is higher in newborns and decreases throughout a lifetime. The average adult range is 3400 to 9600 cells/mm3. Many factors can affect the WBC count.

An increase in the number of normal WBCs is a condition called leukocytosis. Increased WBC counts may normally be seen with pregnancy, stress, anesthesia, exercise, and exposure to temperature extremes, and also after treatment with corticosteroids. Pathologic causes of leukocytosis include many bacterial infections, leukemia, appendicitis, and pneumonia.

A decrease in the WBC count is called leukopenia. This condition may be caused by a viral infection, by exposure to radiation and chemotherapy, or by certain chemicals and drugs.

White blood cell differential

A CBC with differential (or diff) analyzes and counts the number of each type of WBC found in a sample of blood. In the POL, an automated instrument performs the differential. Automated cell counters have the ability to analyze the WBCs and gather information about cell size, internal structures, and density . (In the reference laboratory, the differential can be manually performed using a stained blood smear and a microscope.)

There are five major types of WBCs:

• Granular WBCs
• Neutrophils (polymorphonuclear cells, PMNs, segs, or polys): They are the most abundant WBC in the blood, with a normal adult range of 55% to 70% of the WBC’s. Bands are young neutrophils, and the normal range is 0% to 7% in an adult.
• Eosinophils (eos): They make up about 1% to 4% of the WBCs in an adult.
• Basophils (basos): They make up about 0.5% to 1% of the WBCs in an adult.
• Agranular WBCs
• Monocytes (monos): Monocytes make up about 2% to 8% of the WBCs in an adult. Monocytes are found in the blood, but once they migrate into the tissues, they are called macrophages.
• Lymphocytes (lymphs): Include two types: B cells and T cells. B cells destroy foreign substances (e.g., bacteria, toxins, or viruses) by producing antibodies . T cells target and destroy foreign substances, particularly intracellular pathogen s. Thus, T cells destroy the body’s own cells that have become infected with a disease-causing organism or cancer cells. B and T cells combined are the second most abundant WBC in the blood, making up about 20% to 40% of the WBCs.

Normal values for a WBC differential vary with age. A WBC differential test is used to diagnose a variety of conditions, including autoimmune diseases, inflammatory diseases, leukemia, infections, and anemia. It is a common screening test used as part of a general physical examination.

Platelet count

Platelets are small and irregularly shaped and may vary considerably in size. They have a life span of about 10 days. Platelets are involved with blood clotting. Platelet tests done as part of a CBC include a platelet count, mean platelet volume, and platelet distribution width. These will be described in the following sections.

A platelet count measures how many platelets are in the blood sample. The normal platelet count for an adult is 150,000 to 450,000/mm3. The number of platelets can indicate certain conditions, and it can also be used to monitor the effects of treatments, such as chemotherapy.

Thrombocytopenia is a lower-than-normal platelet count. Low platelet numbers can be related to not enough platelets being made in the bone marrow. It can also be related to the platelets being destroyed in the bloodstream, liver, or spleen. Drugs, medications, cancer treatments, and autoimmune disorders can cause thrombocytopenia.

Thrombocytosis is a higher-than-normal platelet count. Too many platelets can be the result of the following:

• Conditions: Including iron deficiency, infections, cancer, bone marrow disease
• Situations: After surgery, such as a splenectomy, and trauma
• Certain medications

Thrombocytosis can increase a person’s risk for blood clots or other bleeding conditions.

Normal and abnormal test results

It is important for medical assistants to understand the hematology laboratory reports. They should be able to distinguish between normal and abnormal results.

When laboratory test values are at a level that can be life threatening, they are considered critical values. Most ambulatory care facilities have policies and procedures regarding critical values. These values require the laboratory staff to take prompt action and notify the provider of the results. If critical values are called to the provider, the medical assistant may be involved in answering the call, documenting the values, and notifying the provider. When answering the call, usually at least two patient identifiers (e.g., name, date of birth [DOB], or health record number) must be obtained. The medical assistant must document the patient identifiers and the laboratory results and read the information back to the laboratory staff member to ensure the accuracy. The medical assistant must then notify the provider immediately of the results. Both the laboratory staff member and the medical assistant should document the actions they took regarding the critical results.

The medical assistant should never tell patients the laboratory results before the provider is notified of them. The provider will tell the medical assistant what to say to the patient.