I85PREP
⌘ K
Egyptian Board Clinical Pathology study materials
Egyptian Board Clinical Pathology study resources

Egyptian Board Clinical Pathology: Clinical Immunology and Immunopathology

Egyptian Board Clinical Pathology · Work through your exam, one topic at a time.

All guide sections

Clinical Immunology and Immunopathology

Clinical immunology questions test pattern recognition plus assay behaviour: which autoantibody to request, what the result means, and when the assay itself is misleading.

Core rules

  • ANA by indirect immunofluorescence on HEp-2 cells gives a titre and a pattern (homogeneous, speckled, nucleolar, centromere, cytoplasmic); titre and pattern guide but do not diagnose.
  • Anti-dsDNA is specific for SLE; Crithidia luciliae immunofluorescence is specific but insensitive, while ELISA is sensitive and useful for monitoring.
  • The ENA panel (anti-Sm, RNP, Ro/SSA, La/SSB, Scl-70, Jo-1) supports classification of connective tissue disease, not population screening.
  • ANCA: c-ANCA with anti-PR3 is associated with granulomatosis with polyangiitis; p-ANCA with anti-MPO with microscopic polyangiitis; p-ANCA also occurs in inflammatory bowel disease.
  • Anti-CCP is more specific than rheumatoid factor for rheumatoid arthritis; RF occurs in healthy elderly people and in chronic infection.
  • Low C3 and C4 suggest active classical pathway consumption; isolated low C4 may be congenital deficiency.
  • Serum protein electrophoresis alone can miss light-chain disease; add immunofixation and the free light chain ratio (approximately 0.26–1.65).
  • Flow cytometry: report CD4 count with percentage on a single platform; CD4 below 200/µL defines advanced immunosuppression.
  • Primary immunodeficiency work-up: immunoglobulins, lymphocyte subsets, CH50/AH50, dihydrorhodamine test for chronic granulomatous disease.

Worked example

A 60-year-old with sinusitis, pulmonary nodules and haematuria has c-ANCA with anti-PR3. This supports granulomatosis with polyangiitis, but the diagnosis needs compatible clinical or histological criteria, and infection must be excluded first because untreated infection can mimic vasculitis. The antibody is evidence, not the diagnosis.

Traps

  • Using ANA to rule out lupus in a low-probability patient; it is positive in a proportion of healthy people that rises with age.
  • Missing the prozone effect, which gives a falsely low or negative sandwich immunoassay result.
  • Letting IgM rheumatoid factor cause false-positive IgM results in unrelated assays.
  • Reporting an autoantibody without the method and reference range.