Clinical Utility of an Increased Pretreatment Immature Platelet Fraction in the Early Diagnosis of TAFRO Syndrome, Especially in Patients with Late-onset Thrombocytopenia: A Case Series and Literature Review.

Objective The immature platelet fraction (IPF) reflects the thrombopoietic activity and it is useful for diagnosing thrombocytopenic disorders. TAFRO syndrome is a fatal disease that requires an accurate diagnosis and urgent treatment. Thrombocytopenia is essential for the diagnosis of TAFRO syndrome; however, it can develop later during the course of the disease. The significance of IPF and the frequency of late-onset thrombocytopenia in TAFRO syndrome remains unclear. This study investigated the relationship between the platelet count and IPF as well as the absence of thrombocytopenia upon admission for TAFRO syndrome. Methods We herein present the follow-up of our previously reported case and two other cases of TAFRO syndrome with serial IPF measurements performed at our hospital. We reviewed cases published between 2010 and 2024 from the PubMed database. This study included patients diagnosed according to the criteria for TAFRO syndrome proposed in 2019. Results Of the 167 eligible patients, pretreatment IPF was measured in 11, including four with serial measurements. In these 11 patients, the median pretreatment IPF was 18.2% (range 9.8-32.0) and that of the corresponding platelet count was 67,000/μL (range 8,000-179,000). Pretreatment IPF was elevated (≥ 10%) in 10 patients (90.9%), including four without thrombocytopenia. There was no significant correlation between the platelet count and IPF. Thirty-four of 167 patients (20.3%) did not have thrombocytopenia upon admission. Conclusion The pretreatment IPF levels were elevated in most of the patients. Late-onset thrombocytopenia was common. An increased pretreatment IPF level may be a diagnostic indicator of TAFRO syndrome, particularly in patients without thrombocytopenia on admission.