CD19 B cells, absolute count

This test measures the absolute number of CD19 positive B lymphocytes in your blood using flow cytometry. CD45 is a marker that identifies white blood cells, and CD19 identifies B cells, the immune cells that help make antibodies.

The result tells your care team how many B cells you have per microliter of blood, which helps assess the status of your immune system and guides diagnosis and monitoring of conditions that affect B cells.

B cells are key for protecting you against infections by producing antibodies. Doctors order this test if you have frequent or unusual infections, poor responses to vaccines, or if you are being evaluated for an immune deficiency. It is also used to monitor recovery or suppression of B cells during and after treatments that target B cells, such as anti CD20 medicines, stem cell transplant, or chemotherapy.

Low counts may suggest reduced B cell production or increased loss due to inherited or acquired conditions, certain medications, or severe illness. High counts can occur during immune reconstitution, reactive states, or certain blood cancers. Understanding your B cell number alongside other labs and your symptoms helps your clinician decide next steps.

Your result will be compared with the laboratory’s reference interval and interpreted with your age, clinical history, medications, and other immune tests. A lower than expected value does not by itself confirm a diagnosis. Your clinician may review your medications, check antibody levels or vaccine responses, repeat the test, or refer you to an immunology specialist.

If your count is higher than expected, your clinician may correlate with other blood counts, examine a broader lymphocyte subset panel, and consider additional tests if there are symptoms or abnormal findings. Most decisions are based on patterns over time and the whole clinical picture, not a single number.