How should I manage a patient with macrocytosis who is also presenting with neurological symptoms?

Management of a patient presenting with macrocytosis and neurological symptoms should prioritise prompt assessment and treatment of possible vitamin B12 deficiency.

• Do not delay vitamin B12 replacement while waiting for test results if megaloblastic anaemia and neurological symptoms, especially those suggestive of sub-acute combined degeneration of the spinal cord, are suspected.

• Offer an initial diagnostic test for vitamin B12 deficiency if the patient has at least one common symptom or sign (such as macrocytosis or neurological symptoms like paraesthesia, impaired gait, or balance issues) and at least one risk factor for deficiency.

• Interpret vitamin B12 test results using established thresholds: a total B12 concentration less than 180 ng/L (133 pmol/L) or active B12 less than 25 pmol/L confirms deficiency; intermediate results require further evaluation.

• Start vitamin B12 replacement immediately if deficiency is suspected, especially in the presence of neurological symptoms, to prevent irreversible damage.

• Provide information and support to the patient, explaining that symptoms can vary and treatment is effective but may need to be lifelong depending on the cause.

In summary, immediate vitamin B12 replacement should be initiated in patients with macrocytosis and neurological symptoms while awaiting confirmatory tests, followed by appropriate monitoring and support.