The role of platelet parameters in the diagnosis and treatment of immune thrombocytopenic purpura (itp)
Bronchoalveolar Lavage Fluid
ITP is considered to be a disorder of accelerated platelet (pit) destruction with compensating increased pit production. These increased young pits are thought to be larger and more functional, explaining the general lack of bleeding even at very low pit counts (cts). This study explored the utility of pit parameters in patients with ITP including before and after treatment with IVIG. Methods: Pit parameters were measured using the ADVIA 120 (Bayer Diagnostics) including Mean Pit Volume (MPV), Mean Pit Mass per pit (MPM), Pit Distribution Width (PDW) and Large (L) Pits. 13 patients were repeatedly studied before and serially after infusion of 1 gm/kg of IVIG for 2 consecutive days. Results: ITP patients (n=34) were significantly greater than published normals (n= 122) in measurements of MPV ( 11.1 +/-2.9 vs 8.0+/-0.85), MPM (2.45+/-0.53 vs 2.1 +/-0.19), and PDW (63.7+/-17.9 vs 52.S+/-6.8) [all p's < 0.05]. Only 3 pts were < (normal -2D) in MPM suggesting infrequent activation and degranulation. The MPM was greater in the non-splenectomized pts (n=16) than in the splenectomized pts (n=18) [2.62+/-0.63 vs 2.29+/-0.36); there was no difference in the MPV and PDW between these groups. The LOWER the MPV on day 1 (pre-treatment), the higher the pit increase on day 7 after IVIG (p < 0.05). More L-plts on day 1 were correlated with a greater pit increase at 24 hours after 1 infusion of IVIG. Six of 7 pts had a decreased MPM following 1 day of IVIG treatment. The smaller the decrease in MPM at 24 hours, the greater the pit increase on day 7: the 1 pt whose MPM increased at 24 hours had the greatest pit increase (707,000/ul); the same pt had the lowest MPV pre IVIG. Conclusion: Specific pit parameters measured on the Advia 120 distinguished ITP patients from normal. Certain values were correlated with the degree of pit increase after IVIG although the finding of lower MPV and greater pit increase was opposite the starting hypothesis. If newer pits are larger and denser (increased MPV and MPM), then higher values in these parameters would predict increased ongoing thrombopoiesis and greater pit increases with IVIG therapy which acutely blocks pit destruction. The failure of high MPV to predict pit increase calls into question its value as an estimator of thrombopoiesis. The L-plts on day 1 however did correlate with the 24 hour pit increase. Studies are beginning to correlate pit parameters with measurements of pit function since low granularity (low MPM) should indicate "exhausted" and therefore dysfunctional pits.