CRP levels are elevated in immune thrombocytopenic patients and decreased by IVIg treatment, resulting in normalization of platelet counts and reduction of clinical bleeding severity. (A) In humans, CRP levels were also elevated in neonatal FNAIT sera compared with healthy cord blood samples (both n = 21) and sera from newly diagnosed ITP patients compared with age-matched healthy controls (both n = 19). (B-E) Seventy-eight newly diagnosed ITP pediatric patients, all with <20 × 10⁹ platelets/L, were randomized for observation or to receive 0.8 g/kg IVIg. (B) CRP levels did not change significantly in the observation group. (C) However, IVIg treatment caused significant reduction in CRP levels. (D) IVIg treatment also resulted in increased numbers of platelets, which correlated significantly with CRP levels. (E) Similarly, CRP levels correlated significantly with bleeding tendencies, ranging from 0 to 5 (0, no bleeding; 5, life threatening) according to Buchanan et al.⁶⁸  The symbol key for D-E is as follows: black circles, patients when enrolled in the study (diagnosis); red squares, untreated arm 1 week later (1-week observation); blue triangles, IVIg-treated arm 1 week later (1-week IVIg). (F) Elevated levels of CRP at diagnosis predict slower platelet count recovery. Untreated newly diagnosed ITP pediatric patients were retrospectively categorized into normal CRP levels or elevated CRP levels (defined as higher than mean CRP levels of healthy children + 2 times their standard deviation). Statistical comparison was performed with (A) 2-tailed Mann-Whitney test, (B) 2-tailed paired Wilcoxon, (D-E) 1-tailed Spearman’s rank correlation, and (F) 2-tailed Student t test after testing for Gaussian distribution. *P ≤ .05; **P ≤ .01; ***P ≤ .001.