Reticulated Platelet Counts in the Diagnosis of Acute Immune Thrombocytopenic Purpura

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Abstract
Purpose: Bone marrow aspiration is often performed to diagnose childhood acute immune thrombocytopenic purpura (ITP) because no non-invasive investigation to confirm the diagnosis is routinely available. Reticulated platelets (RPs)—young platelets characterized by a high RNA content—increase with increased platelet production and may be useful in the diagnosis of ITP. Methods: To assess the role of RP counts in distinguishing ITP, we compared counts from 15 consecutive patients with ITP with counts from 20 patients with acute lymphoblastic leukemia (ALL), 10 with aplasia, and 27 healthy normal children. Whole blood in edetic acid (EDTA) was labelled with a platelet-specific monoclonal antibody and incubated with thiazole orange (TO). A standard gate was set to achieve a fluorescence value of 1.3 ± 0.5% for control lyophilized platelets. Results: Patients with ITP had a mean (± 1 standard deviation) RP level of 32.9 ± 10.2%; patients with ALL, 6.6 ± 3.1%; patients with aplasia, 3.4 ± 2.0%; and normal patients, 7.9 ± 2.9%. The difference in RPs between the ITP group and the ALL, aplasia, and normal groups was highly significant (p <0.0001 each), with no significant difference between the non-ITP groups (p = 0.12). Conclusions: Measuring RPs by this simple whole-blood cytometric technique discriminated very well between the acute ITP and non-ITP groups. This test has a strong positive predictive value and may prove very useful in the assessment of childhood acute ITP and the screening of candidates for bone marrow aspiration.