Question

What is the major clinical clue that suggests the diagnosis of X-linked agammaglobulinemia (Bruton agammaglobulinemia) in a patient, and which laboratory test result supports this diagnosis?

A. Recurrent viral and fungal infections, low CD19+ cell count
B. Low CD4+ T cell numbers, low CD8+ T cell numbers
C. Presence of preformed antibodies to donor ABO blood group antigens
D. Chronic rejection involving donor endothelial cells

Answer 1

X-linked agammaglobulinemia is diagnosed by recurrent infections with certain bacteria and supported by lab tests showing low CD19+ B cell counts and low or absent serum immunoglobulins.

Step-by-step explanation:

The major clinical clue that suggests the diagnosis of X-linked agammaglobulinemia (Bruton agammaglobulinemia) in a patient is the occurrence of recurrent infections, especially by extracellular bacteria like Haemophilus influenzae, Streptococcus pneumoniae, S. pyogenes, and S. aureus. These infections are primarily due to a lack of specific antibody production. Laboratory tests that support this diagnosis include a low count of CD19+ B cells, which indicates a defect in B cell maturation due to insufficient production of Bruton tyrosine kinase (Btk). Additionally, an absence or very low levels of immunoglobulins in the serum would corroborate the finding since patients with X-linked agammaglobulinemia lack mature B cells that produce these antibodies.