Which investigations are used in combined T and B cell defects?

• A. NBT test
• B. Measurement of chemotaxis
• C. CBC, lymphocyte subsets determination and antibody response to vaccine
• D. Measurement of phagocytosis

Answer: (C)

The key idea is evaluating combined T and B cell defects by assessing both the numbers of lymphocyte subsets and their functional ability to respond to antigens. A CBC gives a general picture of leukocytes, but to identify a combined immunodeficiency you need to know the specific T and B cell compartments. Lymphocyte subset analysis by flow cytometry determines the numbers of T cells (CD3+, with CD4+ helper and CD8+ cytotoxic subsets), B cells (CD19/CD20+), and NK cells, showing whether humoral and cellular arms are affected. Testing antibody responses to vaccines then demonstrates whether those B cells can mount a specific, measurable humoral response, indicating functional humoral immunity.

Tests that focus on neutrophil or phagocyte function, such as the nitroblue tetrazolium test (oxidative burst), chemotaxis, or phagocytosis measurements, assess innate/phagocytic pathways rather than adaptive T and B cell compartments, so they’re not the primary investigations for detecting combined T and B cell defects.