Use of plasma ferritin concentration to diagnose iron deficiency in elderly patients.

AIMS To determine a concentration of ferritin below which the possibility of iron deficiency should be considered in elderly patients. METHODS Consecutive new referrals to a geriatric unit (n = 472) were studied prospectively. Full blood count, ferritin, serum vitamin B12 and red cell folate were measured for all patients. A blood film was assessed independently by three haematologists for features of iron deficiency. For those with ferritin of 12-45 ng/ml, bone marrow aspirates were performed and examined for the presence of stainable iron. When possible, a trial of oral iron was given to those with ferritin of < or = 45 ng/ml and response was determined by re-measurement of full blood count and ferritin after a minimum of three weeks of treatment. RESULTS Bone marrow examination was performed in 32 patients with ferritin of 12-45 ng/ml, of whom 27 (84%) had absent stainable iron, suggesting that most elderly patients with ferritin in this range have iron deficiency. Compared with those with ferritin of 100-299 ng/ml, in whom iron stores were presumed to be normal, patients with ferritin of 12-45 ng/ml had a significantly lower mean haemoglobin and mean red blood cell volume. Furthermore, patients with ferritin up to 75 ng/ml had a significantly higher mean red cell distribution width, and were more likely to have an iron deficient blood film. CONCLUSION Iron deficient erythropoiesis can occur in elderly patients with ferritin up to 75 ng/ml. This is much higher than the lower limit of the "normal" range usually quoted for younger subjects; this difference should be taken into account when ferritin concentrations are interpreted in elderly patients.