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

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Abstract
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.