(P-TS-79) Mathematical Relationship Between Early Immature Platelet Counts Changes and Platelet Count Recovery in Immune-mediated Thrombotic Thrombocytopenic Patients

Background/Case Studies: Immature platelets can be detected by modern fluorescence-capable hematology analyzers in peripheral blood due to their larger size and higher RNA content compared to mature platelets. Measurement of absolute immature platelet counts (A-IPC) has been shown to be useful in thrombocytopenic conditions including thrombotic thrombocytopenic purpura (TTP). New-onset immune-mediated (i)TTP patients have suppressed A-IPC, which begins to recover on average 1-2 days prior to the corresponding mature platelet count change. We set to establish a mathematical formula that allows for the prediction of platelet count based on the change in A-IPC from pre-TPE to Day 1 of TPE.



Study

Design/Methods: Seventeen patients undergoing therapeutic plasma exchange (TPE) for iTTP were used to derive the formula. For each patient, both A-IPC and mature platelet count (PLT) were recorded for all days of treatment. Initial A-IPC change (pre-TPE to Day 1) was used to establish prediction of mature platelet count on day 3 and determine if predicted count was within range of actual platelet count on that day.

Results/Findings: The mean platelet count increased from 16.4×10⁹/L pre-TPE to 39.2×10⁹/L on Day 1, 80.2 ×10⁹/L on Day 2, and 145.4 ×10⁹/L on Day 3. Concurrently, A-IPC rose from a mean of 1.29×10⁹/L pre-TPE to 6.28×10⁹/L on Day 1, 13.0×10⁹/L on Day 2, and 17.6×10⁹/L on Day 3, reflecting marrow activation and thrombopoietic recovery. To assess the relationship between change in A-IPC and mature platelet count, a linear regression model was developed. The change in A-IPC from pre-TPE to Day 1 was used as the independent variable and Day 3 platelet count was the outcome. The postulated equation was: Day 3 PLT=7.65 × (Day 1 A-IPC−Pre-TPE A-IPC) + 96.59

This model demonstrated a positive linear relationship, with a coefficient of determination (R² = 0.34) (Figure 1), indicating that approximately 34% of the variability in Day 3 platelet count could be explained by early A-IPC change. The slope of 7.65 indicated that for every 1-unit increase in A-IPC (×10⁹/L) between pre-TPE and Day 1, there was an average increase of 7.65×10⁹/L in platelet count by Day 3. The intercept (96.59) represents the estimated Day 3 platelet count if there was no A-IPC change. Additionally, testing of 2 other patients established that the predicted count based on formula for patient 1 was 128×10⁹/L and actual count was 131×10⁹/L; for patient 2 predicted count was 102×10⁹/L and actual count was 94×10⁹/L.

Conclusions: Patients with a greater rise in A-IPC within the first 24 hours after TPE were more likely to experience faster platelet recovery by Day 3. A mathematical model to use based on A-IPC change had good prediction accuracy for subsequent platelet counts. These findings highlight the value of A-IPC in patients with iTTP undergoing TPE.