Microcytosis does not predict serum iron concentrations in anaemic dogs

To determine whether microcytosis can be used to predict hyposideremia in dogs, mean corpuscular volume (MCV), iron and total iron binding capacity (TIBC) were measured in 12 control and 45 anaemic dogs. Hyposideremia was found in all dogs with chronic haemorrhage and occasionally in other dogs but mainly associated with inflammation. An ROC curve analysis demonstrated that microcytosis did not discriminate hyposideremic dogs or hyposideremic dogs with normal TIBC from non-hyposideremic dogs. At the optimised cut-off value determined using the ROC curve (MCV=60.9 fL), diagnostic sensitivity, specificity, and positive and negative likelihood ratios were 44.4%, 84.6%, 2.89 and 0.66 for hyposideremia, and 60.0%, 83.0%, 3.53 and 0.49 for hyposideremia not associated with decreased TIBC. The results indicate that microcytosis may not be a hallmark of hyposideremia in dogs.