Evaluation of Platelet Parameters in Children

Introduction: The underlying reason of thrombocytopenia in children should be clarified to initiate effective or to avoid unnecessary treatment. For differential diagnostics the measurement of some relatively new platelet parameters (mean platelet volume - MPV, relative and absolute immature platelet fraction - rIPF and aIPF, plateletcrit - PCT, platelet distribution width - PDW, platelet large cell ratio - P-LCR) may be useful but only limited data are available yet.

Aims: We determined reference values for these parameters in healthy children of different age groups and evaluated the parameters in pediatric thrombocytopenic patients.

Methods: Reference values were determined in 98 apparently healthy children without any medication (43 girls and 55 boys, mean age: 6.3 years, age range: <1 to 16 years) who were allocated to age groups (infants: <1 year, n=12; toddlers: ≥1 year to <6 years, n=41, schoolchildren: ≥6 years, n=44). Data from thrombocytopenic patients were collected retrospectively in 98 children with the following diagnoses: acute ITP (n=19), chronic ITP (n=17), acute leukemia (n=33; 25 with acute lymphoblastic leukemia - ALL, 4 with ALL relapse and 4 with acute myeloid leukemia), inherited impairment of hematopoiesis (n=23; 8 with thrombocytopenia-absent radius syndrome, 6 with inherited thrombocytopenia of unknown origin, 3 with inherited macrothrombocytopenia, 3 with Wiskott-Aldrich syndrome, 2 with Fanconi anemia and 1 with May-Hegglin anomaly) and acquired impairment of hematopoiesis (n=6; 5 with myelodysplastic syndrome and 1 with severe aplastic anemia). Parameters were determined in 200 µl EDTA-anticoagulated blood using the fully automated hematology analyser Sysmex XE 5000 (Sysmex, Kobe, Japan).

Results: In infants platelet count (PLT: 330,000±74,000/µl), rIPF (2.5±1.5%) and aIPF (8,300±5,100/µl) were significantly higher compared to toddlers (PLT: 291,000±52,000/µl; rIPF: 1.6±0.9%; aIPF: 4,700±2,900/µl) and schoolchildren (PLT: 276,000±63,000/µl; rIPF: 2.0±1.2%; aIPF: 5,300±2,500/µl). MPV was significantly lower in toddlers (9.9±0.7 fl) than in schoolchildren (10.6±0.8 fl). For the other platelet parameters no age dependency was detected. The rIPF and aIPF correlated with PDW, MPV and P-LCR. All platelet parameters did not show a gender dependency.

Patients with acute ITP showed significantly lower platelet counts and higher rIPF values compared to the groups of acute leukemia (PLT: 12,000±12,000/µl vs. 87,000±79,000/µl and rIPF: 23.1±9.5% vs. 7.6±4.5%) and of impaired hematopoiesis (75,000±67,000/µl and 12.6±13.6%). Children with chronic ITP displayed significantly elevated rIPF values in comparison with the acute leukemia group (18.5±12.0% vs. 7.6±4.5%) and a significantly increased MPV compared to leukemia patients (12.6±0.9 fl vs. 9.9±0.9 fl) and children with impaired hematopoiesis (10.4±1.5 fl). For aIPF and the other parameters no significant differences among the groups were detected.

Conclusions: Compared to already published pediatric data we detected lower reference values for rIPF and aIPF. In the context of the patient's individual history and a careful clinical examination, the determination of rIPF might be helpful in the thrombocytopenic child to distinguish acute ITP from acute leukemia and a disorder with impaired hematopoiesis. This hypothesis should be investigated in a prospective setting. The relevance of other platelet parameters remains unclear yet.