CBC panel is one of the most common used diagnostic tests in medical practice. When we review it, we should consider that pediatric reference values are different than those for adults, and that they will vary with such factors as age, sex, and height. We should also consider that the reference values include 95% of the “normal” population: that is, the populational mean ± 1.96 standard deviations. Values outside this range do not always imply pathology. Studies have been conducted to determine the CBC reference ranges for the Mexican pediatric population, but there has been no study to determine these ranges for the population with Down syndrome.
Among the systemic alterations associated with Down syndrome are hematological problems. Newborns with Down syndrome have a greater risk for transient neonatal leukemia, known as transient abnormal myelopoiesis (TAM), characterized by circulating blasts with morphological and phenotypic characteristics of leukemic cells. TAM is estimated to occur in approximately 10% of newborns with Down syndrome. Although it is transient, a small number develop serious or even fatal complications such as hepatic fibrosis or edema, and 20% of those who recover from TAM develop acute megakaryoblastic leukemia.
Newborns with Down syndrome may have normal blood counts, although they can show subtle anomalies and dysplastic characteristics of the white corpuscles, platelets, and red corpuscles. These characteristics are often described as incidental findings. Although they are probably not clinically important, the early recognition of non-malignant alterations in these patients is important. To date there are no reference values for different age groups in this population; those reported for the general population have been used in an arbitrary way.
Other hematological alterations that have been found in newborns with Down syndrome include neutrophilia, thrombocytopenia, and polycythemia, with incidences of 80%, 66%, and 34%, respectively, reported by Henry et al. These anomalies generally have a benign clinical course and resolve spontaneously at three weeks of age. The neutrophilia is slight, rarely over 30.000/µL, and is not associated with an infection. The thrombocytopenia is also slight, the majority with platelet counts < 150 000/µL, and is not associated with hemorrhage. Kivivuori et al. carried out a prospective follow-up study of the platelet counts of twenty-five newborns with Down syndrome during their first year of life and found that thrombocytopenia is generally brief, resolves itself in the first few weeks, and is later replaced by thrombocytosis. Polycythemia is usually slight, and only some presented cyanosis, which is corrected with partial exchange transfusion. It is usually independent of the heart defects and hypoxia that are often associated with this condition.
Our study included only twenty-six newborns; none of them presented polycythemia, only one with neutrophilia (3.8%), and three with thrombocytopenia (11.5%), a contrast with the findings of Henry et al. However, the small size of our sample in this age group must be considered.
At later ages, anemia, macrocytosis, and leukopenia were common in our sample, at levels like those previously reported by Roizen and Kivivuori[8,9]. High levels of mean corpuscular volume have been reported in patients with Down syndrome at all ages. David et al. found no underlying cause for macrocytosis and postulated an altered folate remethylation path as an effect of greater cystathionine-β-synthase activity. Our findings coincide with these studies. Evaluation of a patient with anemia should consider its possible underestimation due to macrocytosis, and consider the use of other tools, such as analysis of folates, vitamin B12, and iron for greater diagnostic certainty.
Finally, we observed some hematological alterations not previously reported for patients with Down syndrome: lymphopenia, eosinopenia, basophilia, neutrophilia, and neutropenia. Although these have no clinical significance, they should be monitored.