To the Editor.—
The excellent article by Drs Steinberg and Dreiling, which emphasized the significance and evaluation of RBC microcytosis, was incomplete in one respect. It failed to list among the possible causes those disorders involving RBC fragmentation. Although uncommon, this association has been reported by David Bessman in The Journal (1978; 239:2475). The specific case that Dr Bessman analyzed involved a severe burn, but he also noted in the literature the mention of a "low MCV [mean corpuscular volume] in the hemolytic-uremic syndrome." He went on to mention that RBC "fragmentation is rarely so severe as to cause" an MCV of 70 cu μm or less; "however, lesser degrees of fragmentation may depress the MCV less yet be detectable." I would only add that lesser degrees of RBC fragmentation do not necessarily denote the presence of diseases of lesser severity.