A clinical history of recurrent, chronic, or atypical infections (and failure to thrive in children) should prompt the measurement of serum immunoglobulins and other tests for immunodeficiency. The presence of hypogammaglobulinaemia should be confirmed on repeat testing. Any underlying secondary causes should be excluded before referral to a consultant immunologist for investigation of primary immunodeficiency (PID). The referral centre will establish whether there is a known genetic cause, and if there is impaired antibody function in addition to the low immunoglobulin levels. The extent of organ involvement and chronic damage should also be assessed.

In some cases, the presence of hypogammaglobulinaemia may be an incidental finding on a screening blood test. Under such circumstances, a similar approach (of confirming the result, assessing infection history, and excluding secondary causes) should be used, with subsequent referral to an immunologist.

Severe combined immunodeficiency (SCID) is a medical emergency, and patients should be urgently referred to specialist centres for confirmed diagnosis and treatment as soon as it is suspected (i.e., if patients have low absolute lymphocyte counts and low immunoglobulins).

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