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Blood Test Tracker

CD19+ B Cells, absolute

How many B cells are in a microliter of blood. B cells are the white blood cells that grow into antibody-making cells.

AI-verified against cited sources. Awaiting expert reviewAlso called Abs CD19LOINC 8116-6

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What it is

B cells are lymphocytes, a type of white blood cell. When they meet a germ, they mature into plasma cells that make antibodies. Labs count them with flow cytometry by looking for the protein CD19 on their surface. Some labs report CD20 instead, which marks most of the same cells but is a separate test. This page covers the absolute count, shown as cells per microliter of blood.

Why it matters

B cells are the source of your antibodies, so this count helps show whether the body can make them. It is part of a lymphocyte subset panel with T cells and NK cells. Clinicians use it when someone has repeated infections, when an antibody problem is suspected, and to follow treatments that remove B cells. It is read together with antibody (immunoglobulin) levels and your symptoms.

If it’s low

A low B-cell count means fewer of these cells than usual in the sample. It is expected during treatment that targets B cells, such as anti-CD20 antibodies. Otherwise it can follow illness or other immune-suppressing medicines. Less often, it is linked to an inherited antibody condition.

Common causes

  • B-cell-targeted treatment such as anti-CD20 antibodies (for example rituximab)
  • Other immune-suppressing medicines or chemotherapy
  • Recent illness
  • A low total lymphocyte count
  • Inherited antibody conditions such as X-linked agammaglobulinemia, where B cells are usually below 1% of lymphocytes

What can help

  • If you are on B-cell-targeted treatment, ask your clinician what level they expect and how they use this count
  • Ask whether antibody (immunoglobulin) levels should be checked alongside it

If it’s high

A mildly high B-cell count is often temporary, for example during or after an infection. A count that stays high, or comes with other changes in your blood counts, is something a clinician may look into further.

Common causes

  • Normal variation between people
  • Recent or ongoing infection
  • Less often, a blood condition that makes too many B cells, usually found together with other blood count changes

What can help

  • Ask your clinician whether to repeat the test after any recent illness has passed
  • Bring your complete blood count so the results can be read together

Usual ranges

What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.

The usual range depends on age. Choose an age to see the one that applies.

Children and teens 9 ranges
  • under 0.01940–1,100 cells/µL

    Source: Labcorp

  • 0.019–-0.833600–1,900 cells/µL

    Source: Labcorp

  • 0.167–-0.583600–3,000 cells/µL

    Source: Labcorp

  • 0.417–-0.25700–2,500 cells/µL

    Source: Labcorp

  • 0.75–0.25600–2,700 cells/µL

    Source: Labcorp

  • 1.25–1600–3,100 cells/µL

    Source: Labcorp

  • 2–4200–2,100 cells/µL

    Source: Labcorp

  • 5–9200–1,600 cells/µL

    Source: Labcorp

  • 10–15200–600 cells/µL

    Source: Labcorp

See B cells (absolute) by age and sex, with the U.S. survey numbers where they exist.

What can affect your result

  • Recent infection or illness
  • B-cell-targeted treatment such as anti-CD20 antibodies, other immune-suppressing medicines and chemotherapy
  • Age: children have much higher counts than adults
  • Time of day
  • Method: bead-based counts versus counts calculated from a separate CBC lymphocyte count
  • Whether the lab counts CD19+ or CD20+ B cells (separate tests that mark most of the same cells)
  • The sample must stay at room temperature and reach the lab quickly: Labcorp asks for arrival within 48 hours, and ARUP lists 72 hours in EDTA tubes and 48 hours in heparin tubes. Refrigerated, frozen, hemolyzed or clotted samples are rejected (Labcorp, ARUP).
  • B-cell-targeted treatment, other immune-suppressing medicines, chemotherapy and recent infection can change counts.
  • Counts calculated from a separate CBC lymphocyte count inherit that count's variation.

Counts can shift over the day, so a similar time of day helps when you compare repeat results. Counts can change over days to weeks with illness. B-cell-targeted treatment lowers them, and they can take months to return.

When to talk to a clinician

Talk with your clinician if you have repeated, severe or unusual infections, or if your B-cell count is well outside your lab's range. Get urgent care for a high fever with shaking chills, trouble breathing, confusion or an illness that is getting worse fast.

Questions you could ask

  • Why was this panel ordered for me, and what are you looking for?
  • How should I read this alongside my T-cell and NK-cell results?
  • Could a recent infection explain this count?
  • Should we repeat the test or review my other blood counts?
  • Could my treatment or a recent illness explain this result?
  • Should my antibody (immunoglobulin) levels be checked as well?

Questions people ask

My report says CD20 instead of CD19. Is that the same?

Both proteins mark B cells, and the two counts are usually close, but they are separate tests. Your report shows which one your lab used. If you are on a treatment that targets B cells, ask your care team which count they follow.

Why would my B cells be counted during treatment?

Some treatments are designed to remove B cells. The count shows whether they are cleared and when they start to return. How the result is used depends on your condition and your care team.

Show the science and sources

Units

  • 1 cells/µL = 1 cells/µL
  • 1 cells/µL = 0.001 ×10³/µL
  • 1 cells/µL = 0.001 ×10⁹/L
  • 1 cells/µL = 1 ×10⁶/L

Open the B cells (absolute) unit converter

For clinicians and researchers

CD19 is a pan-B-cell surface marker. Some labs report CD20 instead, which marks most of the same circulating B cells but is a separate assay. Absolute counts come from single-platform bead-based flow cytometry or are calculated as the B-cell percentage times the CBC absolute lymphocyte count (dual platform), which carries the CBC's variation. Reference intervals are lab- and method-specific. Labcorp's adult interval was set by the lab, and its pediatric rows come from Comans-Bitter et al. (J Pediatr 1997). ARUP's adult interval is higher at the low end. In X-linked agammaglobulinemia, T and NK counts are normal while B cells are usually undetectable or below 1% of lymphocytes (Salzer 2019). B-cell depletion is expected on anti-CD20 therapy. Because those antibodies bind CD20 itself, some centers follow B cells by CD19 during that treatment. Specimen: whole blood at room temperature (Labcorp: lavender EDTA plus yellow ACD tubes, received within 48 hours; ARUP: EDTA, stable 72 hours, or heparin, stable 48 hours).

LOINC 8116-6 (primary), 15195-1. Specimen: whole-blood.

Sources

  1. T- and B-Lymphocyte and Natural Killer Cell Profile (test 505370), Labcorp
  2. Flow Cytometry in the Diagnosis and Follow Up of Human Primary Immunodeficiencies, EJIFCC (International Federation of Clinical Chemistry and Laboratory Medicine) (2019)
  3. Lymphocyte Subset Panel 5 - Total Lymphocyte Enumeration (test 0095892), ARUP Laboratories

AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.

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