Your healthcare provider will diagnose lymphopenia based on your medical and family health histories, a physical exam, and test results. Newborn screening may lead to early diagnosis of diseases that can cause life-threatening lymphopenia.
A low lymphocyte count alone may not cause any symptoms. The condition often is found during a routine checkup or when your healthcare provider tests you for other diseases or conditions. In other cases, your provider may order tests to diagnose lymphopenia after noticing that you have unusual infections, repeat infections, or infections that do not heal quickly.
Medical history and physical exam
Your provider will do a physical exam to look for signs of infection, such as fever. They may check your stomach for signs of a that is larger than normal and your neck or armpits for signs of that are larger than normal.
Your provider also will look for symptoms of diseases and conditions that can affect your lymphocyte count, such as HIV and blood cancers.
Your provider may ask:
- About your risk for HIV infection such as intravenous (IV) drug use, sexual partners, exposure to infectious blood or bodily fluids at work, or blood transfusions
- Whether you've ever had treatments such as radiation, chemotherapy or immunotherapies
- Whether you've ever been diagnosed with a blood disease or immune disorder, or whether you have a family history of such illnesses
- About your diet and other lifestyle habits
Your healthcare provider may recommend tests to help diagnose a low lymphocyte count. Some of these tests may need to be repeated.
- A complete blood count with differential checks the numbers of lymphocytes, as well as , , and other types of in your blood.
- Flow cytometry measures the levels of the different types of lymphocytes — T cells, B cells, and natural killer cells. This helps healthcare providers find the underlying cause of lymphopenia.
- Immunoglobulin level tests check the levels of antibodies called immunoglobulins, made by B lymphocytes. The total levels may be low due to low counts of B lymphocytes, or some groups of B cells, although present, may be dysfunctional and not produce normal amounts or some fractions of antibodies.
- Other tests can check for different diseases that cause lymphopenia such as HIV, COVID-19 or other viruses, tuberculosis, or other blood or immune conditions. Your provider may also test your bone marrow or your .
What the numbers mean
Healthy levels of lymphocytes are different for adults and children, and may vary more based on your age or overall health.
- Adults: A normal lymphocyte count usually is between 1,000 and 4,800 lymphocytes per microliter of blood. Your provider may diagnose you with lymphopenia if you have less than 1,500 lymphocytes per microliter of blood for adults.
- Children: A normal lymphocyte count is variable depending on the child’s age. The percentage and absolute lymphocyte counts are higher in very young children. Your child age 6 and younger may have lymphopenia if they have less than 2000 lymphocytes per microliter of blood.