FRCPath Haematology Part 1 MCQs - Gen Haematology 438

A 51-year-old man is referred to the haematology clinic with a 9-month history of fatigue, night sweats, intermittent diarrhoea, and a 7-kg weight loss. Examination reveals moderate splenomegaly but no lymphadenopathy.

Full blood count shows:

• Hb 118 g/L

• WBC 28.5 ×10⁹/L

• Neutrophils 10.2 ×10⁹/L

• Eosinophils 11.8 ×10⁹/L

• Platelets 520 ×10⁹/L

Blood film confirms marked eosinophilia without significant dysplasia. Bone marrow examination demonstrates a hypercellular marrow with eosinophilic proliferation and increased spindle-shaped mast cells. Cytogenetic analysis reveals a normal karyotype.

Further investigations show:

• Vitamin B12: markedly elevated

• Serum tryptase: 42 ng/mL (normal <11)

• Stool microscopy ×3: negative

The most appropriate next investigation to establish the diagnosis and guide therapy is:

A. KIT D816V mutation analysis on bone marrow aspirate

B. T-cell receptor gene rearrangement studies

C. Peripheral blood FISH or RT-PCR for FIP1L1-PDGFRA

D. JAK2 V617F mutation analysis

E. Serum IgE measurement