Screening for hereditary spherocytosis by use of automated erythrocyte indexes,☆☆

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Abstract

Objective: To determine whether the mean corpuscular hemoglobin concentration (MCHC) or other erythrocyte indexes, as determined by automated cell counters, remains a useful screening test for identifying patients with hereditary spherocytosis (HS).

Methods: Erythrocyte indexes from 112 children with HS who had not undergone splenectomy were compared with those measured in an equal number of healthy, age-matched children. All indexes were derived from measurements obtained by aperture impedance.

Results: Mean corpuscular hemoglobin concentration in the HS group was 35.9 gm/dl, significantly higher than in normal control subjects (34.3 gm/dl; p <0.001). Mean erythrocyte distribution width also was significantly higher in patients with HS (19.3 vs 12.6; p <0.001). The MCHC distinguishes individuals with HS, with an area under the receiver operating characteristic curve of 0.86. Although not disease specific, an erythrocyte distribution width >14 has 85% sensitivity and 97% specificity and an area under the receiver operating characteristic curve of 0.92. An MCHC >35 gm/dl has a sensitivity of 70% and a specificity of 86%. Combining the MCHC and erythrocyte distribution width increases the area under the receiver operating characteristic curve to 0.97. Specificity is 100% and likelihood ratio is infinite when both the MCHC and erythrocyte distribution width are elevated.

Conclusions: The automated MCHC is an effective screening test to identify children with HS. An elevated erythrocyte distribution width adds additional specificity and is itself a powerful screening tool. The combination of the two tests is an excellent predictor for the diagnosis of HS. (J Pediatr;130:957-60)

Section snippets

Subjects

We reviewed the outpatient medical records of children followed up regularly between 1989 and 1995 at the Children's Hospital of Philadelphia Hematology Clinic for HS. Hereditary spherocytosis was diagnosed on the basis of clinical history, peripheral blood examination, and reticulocyte count, and was confirmed by RBC osmotic fragility. Hemoglobin, hematocrit, MCV, MCHC, RDW, and reticulocyte count were documented from the clinic visits of 128 patients. Data from patients younger than 12

RESULTS

Means and standard deviations of the age, hemoglobin level, RBC indexes, and reticulocyte counts are shown in Table I. Patients with HS who have not undergone splenectomy have a significantly lower mean hemoglobin concentration and a significantly higher MCHC and RDW than normal control subjects.

Hematologic characteristics of patients with HS who had splenectomy and those who did not are also shown in Table I . The group without splenectomy is significantly younger than the splenectomy group.

DISCUSSION

Although no extensive information is available on the use of the automated RBC indexes in the differential diagnosis of microcytic anemias, little attention has been given to their role in the diagnosis of other anemias. In a once active debate over the utility of the automated MCHC in the microcytic anemias, it was assumed that this index was helpful in the diagnosis of HS. 5, 6, 9 However, there is evidence that electronic cell counters underestimate the MCHC with increasing error as the MCHC

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Reprint requests: Catherine S. Manno, MD, Division of Hematology, Children's Hospital of Philadelphia, 324 S. 34th Street, Philadelphia, PA 19104.

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