What are the indications for referring a patient with macrocytosis to a haematologist?

Indications for referring a patient with macrocytosis to a haematologist include:

• Presence of unexplained macrocytosis after initial assessment and exclusion of common causes such as vitamin B12 or folate deficiency, liver disease, or alcohol excess.
• Macrocytosis associated with additional abnormal blood counts, such as leukopenia or thrombocytopenia, which may suggest bone marrow pathology.
• Clinical features or blood test results suggestive of myeloma or other haematological malignancies, such as persistent bone pain, raised plasma viscosity, abnormal serum protein electrophoresis, or serum free light chain abnormalities.
• Macrocytosis with neurological symptoms or signs that are not explained by vitamin B12 deficiency alone, warranting specialist haematological evaluation.

Referral should be considered when initial investigations do not clarify the cause of macrocytosis or when there is suspicion of serious underlying haematological disease requiring specialist management.

Vitamin B12 deficiency is a common cause of macrocytosis, but absence of anaemia or macrocytosis does not exclude deficiency, and clinical judgement is required to decide on testing and referral ².

Referral pathways for suspected haematological malignancies such as myeloma should follow the suspected cancer pathway if indicated by clinical features and laboratory findings ¹.