To re-evaluate the red cell diameter width distribution (RDW) to help predict iron, vitamin B12 and folic acid deficiency in the older person (>65years old).

Cross-sectional analysis of haematological parameters in old subjects with iron, vitamin B12 and folic acid deficiencies.

District General Hospital in Harrow, Middlesex, United Kingdom.

Subjects (both inpatient and outpatient) where haemoglobin and haematinics (ferritin, vitamin B12 and red cell folate) were undertaken as part of investigative work-up.

We evaluated the RDW, microcytosis, macrocytosis and haemoglobin (Joosten anaemia) in subjects with the above deficiencies.

Two hundred and forty-eight older subjects were retrospectively identified and categorised as definite iron, probable iron, vitamin B12, B12 and probable iron and folate deficiency.

Raised RDW was superior to microcytosis in predicting iron status in both definite iron (χ²=21.3, P<0.0001) and probable deficient group (χ²=30.0, P<0.0001). RDW was also superior to macrocytosis in predicting B12 (χ²=12.2, P=0.0005) and folate status (χ²=10.6, P=0.001). Similarly, RDW was better than Joosten anaemic criteria for iron deficient (χ²=4.08, P=0.04), probable iron deficient (χ²=9.3, P=0.002), combined B12 and probable iron deficiency (χ²=4.7, P=0.03), folate deficiency (χ²=5.9, P=0.015) but not for B12 deficiency (χ²=0.05, P=0.83).

Although RDW lacked sensitivity, it is the most useful haematological parameter to alert clinicians to check the haematinics to determine anaemic type in the older person.