Laboratory Evaluation of B cell Function
What laboratory tests are performed to evaluate the integrity of the humoral immune system (B-cell function)?
A simple initial screen for hypogammaglobulinemia is to subtract the albumin from the total protein and see if it is <1.5 g/dL. A reasonable screen for the evaluation of B-cell function is to determine the serum IgA level and perform the inexpensive in vivo functional tests. If all these tests are normal, clinically significant B-cell dysfunction may be reasonably excluded. If IgE is normal, a class-switching defect is unlikely. If any of these tests are abnormal, further testing to characterize B cell development and referral to clinical immunology is appropriate. As with rheumatologic evaluations, further testing to diagnose a disease requires objective evidence for tissue or end-organ involvement.
Laboratory Evaluation of B cell Function
| Category | Specific Tests | Comments |
|---|---|---|
| In vivo functional tests (routine screening tests) | Isohemagglutinin titers (anti-blood group A and B) | Naturally occurring; predominantly IgM |
| Diphtheria and tetanus booster immunization | Serum antibodies assayed prior to and 2 weeks later; assesses capacity to synthesize IgG antibodies against protein antigens | |
| Pneumococcal immunization | Serum antibodies assayed prior to and 3 weeks later; assesses capacity to synthesize antibodies against polysaccharide antigens. Currently no formal consensus on the reference ranges for normal. | |
| Immunoglobulin quantitation | IgM, IgG, IgA levels | Various immunoassays may be used; readily available |
| IgG subclass, IgE levels | ELISA and RIA available (expensive) | |
| In vitro tests (expensive) | Peripheral blood total B cells | Flow cytometry, CD19+ B cell numbers |
| B cell subsets | Class-switched memory B cells (CD27+ + IgD-) versus non-switched memory B cells (CD27+ + IgD+) and immature or transitional B cells | |
| Genetic testing BTK (XLA), CVID, CID with monogenetic cause | In vitro immunoglobulin synthesis | Peripheral blood mononuclear cells stimulated in vitro with pokeweed mitogen (not frequently for clinical decisions) |
ELISA, enzyme-linked immunosorbent assay; RIA, radioimmunoassay.
