2025 – PAGE 117 – 118 – ALLERGY & IMMUNOLOGY

IMMUNOLOGY TESTS, A RECAP

SKIN TESTING

Skin testing WITH PURIFIED PROTEIN DERIVATIVE (AKA PPD, AKA TUBERCULIN SKIN TEST), CANDIDA, MUMPS, and TETANUS can all be used to diagnose Delayed-type hypersensitivity ANERGY. This checks for Type IV, CELL-MEDIATED IMMUNITY. T-cell mediated immunity includes activation of antigen-specific cytotoxic T-lymphocytes, macrophages, and natural killer (NK) cells. This includes CD4 cells and problems that arise from HIV/AIDS.

TITERS

If you suspect a B-cell (AKA Humoral) deficiency, test for it by obtaining antiBody TITERS for something the child was already immunized against, such as TETANUS. (Testing for tetanus titers in patients with Agammaglobulinemia, a B-cell deficiency, is an ABP favorite way of testing your knowledge.) You could also test for titers against Diphtheria and Streptococcus/Pneumococcus. Do not get confused with getting SKIN TESTING for tetanus/Candida/Mumps/PPD, which all test for T-cell mediated (AKA cellular) immunity.

PEARLS: 

• Infections related to B-cell deficiencies rarely occur before 6 months of age because the maternal antibodies are present.
• ANTIBODY SUBCLASSES: If IgG levels are in the normal range, but you still have a high suspicion for a B-cell/Humoral defect, consider checking for the presence of Ig subclasses for Tetanus, Pneumococcus, etc.

CH50

CH50 is a great screen to test the entire complement system. Order this if a patient has repeated, serious pyogenic/bacterial infections.

NITROblue TETRAZOLIUM (NBT)

NITROblue Tetrazolium (NBT) test is to test for Chronic Granulomatous Disease (CGD). Dihydrorhodamine (DHR) Fluorescence can also be used.

MNEMONIC: “NEUTROblue” referring to “ChroniX GranulomatuX Disease” being a NEUTROphil disorder. NITROblue is a reminder of the “NITROglycerine” oxidative burst defect. BLUE is a reminder that this disease has an association with colors (RED = the color that SERRATIA makes).