Macrocytic anaemia (MCV 103) with neurological features (tingling/paraesthesia, absent reflexes, weakness, poor concentration) is vitamin B12 deficiency: demyelination causes subacute combined degeneration, peripheral neuropathy and neuropsychiatric change. Folate deficiency is the tempting alternative because it is also megaloblastic, but it has no symptoms beyond the anaemia itself. Iron deficiency is microcytic.