Spurious red blood cell parameters due to serum cold agglutinins: observations on Ortho ELT-8 cell counter.

The pattern of spurious red blood cell parameters caused by serum cold agglutinins has been well characterized for the Coulter counters but not the Ortho ELT-8. The pattern consists of a spurious increase in mean corpuscular volume (MCV), a discrepancy between the hemoglobin and the hematocrit, the latter falsely reduced and consequently a MCHC value greater than 36%. Since MCHC rarely exceeds 36% in health or disease, it is an important clue to the spurious nature of the macrocytosis caused by cold agglutinins. The authors have studied five examples of cold agglutinin induced artefact on the Ortho ELT-8 counter. Although a pattern similar to that for the Coulter counters was anticipated, three of the five patients failed to show the characteristics "internal discrepancy" and a MCHC value greater than 36%, despite a marked spurious elevation of MCV. In two of the three patients a classical pattern of cold agglutinin artefact was observed on a Coulter S Plus IV counter with only a modest elevation of MCV. Possible explanations for the observed pattern on the ELT-8 and its implications are discussed.