Immature platelets-also termed reticulated platelets (RP)-are platelets newly released into the circulation, and have been associated with a variety of pathological bleeding events including primary immune thrombocytopenia (ITP). They can be assessed by flow cytometry (FCM) after staining with thiazole orange (TO) at low concentration and expressed as a fraction of the total platelet count (RP%). The diagnosis of primary ITP is based on differential diagnosis and the measurement of RP% can serve as an alternative diagnostic test that are useful in daily practice. Our study aimed at distinguishing primary ITP from other thrombocytopenic disorders, especially aplstic (hypoplastic) or chemotherapy-induced thrombocytopenia by FCM. The sensitivity and specificity of the assay as well as agreement between RP% measurement and monoclonal antibody-specific immobilization of platelet antigen (MAIPA) were analyzed accordingly.

The investigators are undertaking a multi-center, prospective blind trial of 500 adults with thrombocytopenic disorders with a platelet count less than 60*10^9/L from 4 medical centers in China. In brief, 15 μl aliquots of anti-coagulated whole blood were incubated for 70 min with 5 μl of phycoerythrin-conjugated anti-CD42b monoclonal antibody (BD Pharmingen, Tokyo, Japan) and 1 ml of thiazole orange (Retic-COUNT; Becton-Dickinson, San Jose, CA, USA) diluted 10 times by phosphate-buffered saline. RP% was analyzed on a flow cytometer (FACScan, Becton-Dickinson) by measuring 10,000 events in the CD42b-positive fraction.

Clinical information of all participants including gender, age, platelet count and definitive diagnosis were recorded by an exclusive investigator. RP% results were revealed at the end of recruitment and after all FCM measurements were completed. The agreement between clinical diagnosis and RP% results were analyzed to identify primary ITP.

Inclusion Criteria:

1. Untreated adult patients of both gender between the ages of 18 and 75 years
2. Each participant showed a platelet count 60*10^9/L, with or without bleeding manifestations
3. Thrombocytopenic disorders including autoimmune-mediated, aplastic (hypoplastic) or chemotherapy-induced thrombocytopenia

Exclusion Criteria:

1. Received high-dose steroids or IVIG within 3 weeks prior to the test
2. Received second-line ITP-specific treatments (eg, cyclophosphamide, 6-mercaptopurine, vincristine, vinblastine, etc) within 3 months prior to the test
3. Current HIV infection, hepatitis B virus or hepatitis C virus infections
4. Severe medical condition (liver and kidney function impairment). Unstable cardiovascular disease or uncontrolled hypertension.
5. Patients who are deemed unsuitable for the study by the investigator

500 adults with thrombocytopenic disorders with a platelet count less than 60000/uL from 4 medical centers in China.