If you think that you or your child may have an undiagnosed PID, you should ask your GP to test for immunoglobulin levels. The UKPIPS Medical Advisory Panel have written a leaflet on diagnosing a PAD which can be found here xxxxx. If these tests come back in any way suspect, your GP should discuss the results with their nearest clinical immunologists. A list of clinical immunologists can be found here xxxxxx
People whose basic immunoglobulin test appears normal but who continue to have repeated infections should ask their GP to refer them to a Consultant Clinical Immunologist, as some Primary Immune Deficiencies can only be diagnosed with more complex tests which are not available to GPs.