The unreliability of mean corpuscular volume and mean cellular hemoglobin determinations in the diagnosis of alpha-thalassemia in newborn infants

The erythrocyte indices of neonates, defined using data from over 12,000 patients in a multihospital health care system

OBJECTIVE

The erythrocyte indices (mean corpuscular volume (MCV), mean corpuscular hemoglobin concentration (MCHC) and mean corpuscular hemoglobin (MCH)) were originally reported using hand-calculated values, based on a centrifuge-spun hematocrit, a counting-chamber erythrocyte count and a hemoglobin concentration measured by any number of hemoglobinometry methods. Modern blood cell analyzers measure the MCV, and calculate the MCHC and MCH, on the basis of logs higher sample sizes than employed in the original methods.

STUDY DESIGN

With a single type of automated blood cell counter (Beckman Coulter LH 750; Fullerton, CA, USA), we determined the ranges of erythrocyte indices among neonates of 22 to 42 weeks gestation. Data were accumulated during a 3-year period from a multihospital health care system, using all indices reported on untransfused neonates during their first day of life.

RESULT

Erythrocyte indices were obtained from 17,634 tests performed on 12,016 neonates. The MCV and the MCH decreased with advancing gestational age. For instance, the MCV diminished from 119+/-7 fl (mean+/-s.d.) in neonates < or =25 weeks gestation to 106+/-4 fl at 40 weeks. The MCH diminished from 40+/-2 pg in neonates < or =25 weeks gestation to 36+/-2 pg at 40 weeks. The MCHC did not change appreciably with gestational age (34+/-1 pg dl(-1)).

CONCLUSION

The results describe the expected values for erythrocyte indices on the first day of life among untransfused neonates. Additional study is needed to determine the relevance of very high or low erythrocyte indices in this population and to understand any physiological advantage of these very large erythrocytes during fetal development.

The different types of alpha-thalassemia: practical and genetic aspects

From May 1985 to October 1987, 1,564 Southeast Asians living in Hawaii were screened for hereditary anemias. Microcytosis was determined by electronic red cell indices and morphology; iron deficiency was ruled out by normal red cell distribution width and normal protoporphyrin levels; Hb E was determined by electrophoresis; beta-thalassemia (thal) heterozygotes were identified by raised Hb A2 on column chromatography. alpha-Thalassemia heterozygotes were diagnosed by exclusion. Family studies helped identify or confirm diagnoses, especially for the alpha-thal-2 heterozygotes (-alpha/alpha alpha) and homozygotes (-alpha/-alpha). Provisional diagnoses are being checked by DNA analyses. Iron deficiency prevented detection of possibly coexisting alpha-thalassemias in 97 individuals. Technical problems included the obscuring of standard criteria for recognizing the alpha-thal variants by the presence of Hb E or beta-thal. In such cases, alpha-thal could only be detected by family studies or DNA analyses. Problems with hemoglobin (Hb) electrophoresis included Hb H migrating beyond the edge of the strip if incubation was not closely monitored, and difficulty in detecting the small amounts of unstable Hb Constant Spring. DNA analyses also had limitations, since the nondeletion alpha-thalassemias would not be detected by routine Southern blotting. DNA analyses suggested that about 50% of presumed alpha-thalassemias were alpha-thal-2 (-alpha/alpha alpha) variants, and a corresponding number of alpha-thal-2 variants were among the apparent normals. Gene frequencies in the unselected Lao subjects were approximately 0.2 for Hb E, at least 0.1 for (-alpha), usually a rightward (alpha -3.7) type, 0.04 for (-), and 0.01 for a beta-thal. Multistep screening for the alpha- and beta-thalassemias was an effective and efficient strategy.