Plasma calprotectin to assess susceptibility to bloodstream infections during paediatric acute lymphoblastic leukaemia induction treatment

Chemotherapy-induced neutropenia, monitored by peripheral blood absolute neutrophil count (ANC), increases the risk of bloodstream infections (BSIs). However, ANC may not reflect the total neutrophil population, as it omits neutrophils at extravascular sites. We therefore evaluated plasma calprotectin, a neutrophil-derived protein, as a complementary marker of neutropenia severity and BSI risk. In 114 children with acute lymphoblastic leukaemia (ALL) treated according to the NOPHO ALL2008 protocol, plasma calprotectin was measured weekly during the 4-week anthracycline-based induction therapy. Daily ANC and BSI events were obtained from medical records. All patients developed profound neutropenia (ANC <0.5 × 10⁹/L). At the time of BSI occurrence (median day 12), ANC did not differ between patients with BSI (n = 29, 25%) and those without. Although calprotectin declined in parallel with ANC, the correlation was only modest (r_s: 0.20–0.53, all p < 0.05). A sex-, age- and risk group-adjusted multivariable analysis showed significantly lower calprotectin levels in patients with BSI at days 1, 8 and 15 (all p < 0.05). Each twofold decrease in calprotectin increased BSI risk with odds ratio (OR) 1.52 (1.07–2.15), p = 0.018. In conclusion, reduced plasma calprotectin was associated with BSI during ALL induction therapy and may provide clinically relevant information beyond ANC to assess immunosuppression and guide antimicrobial strategies.