NT-proBNP course during MIS-C post-COVID-19: an observational study.

Multisystem inflammatory syndrome in children (MIS-C or PIMS-TS) is a severe disease. N-terminal pro-B-type natriuretic peptide (NT-proBNP) is used for positive and differential diagnosis, diagnosis of complications and severity, and cardiogenic shock prediction. However, contrasting cut-offs have been suggested. The aims of the present study were to compare NT-proBNP values depending on the time of measurement and to describe the NT-proBNP course during the MIS-C episode. The data from a single-centre cohort observational study on the impact of time to diagnosis, defined as the time from first symptom to diagnosis of MIS-C, were used for the purpose of this study, with an extended period of inclusion from May 2020 to April 2023. The timing and level of all NT-proBNP samples available for each patient were retrospectively collected. Thirty-seven children (18 (49%) females, median age 8.8 years, 14 (38%) with shock) were included. Until diagnosis, NT-proBNP increased with time and was significantly higher at 6 days from first symptoms than at 3 days (median (interquartile range) 32,933 (7773-61,592) versus 1994 (1291-4190) pg/mL, respectively, p = 0.031). From diagnosis, NT-proBNP decreased by at least 50% after 3.0 (2.1-5.3) days (n = 12) when NT-proBNP at diagnosis was low ≤ 11,000 pg/mL versus 1.8 (0.7-3.4) days (n = 16) when NT-proBNP at diagnosis was high (p = 0.040), and after 3.6 (2.4-5.9) days (n = 7) when fever persisted after 48 h versus 1.8 (0.8-3.0) days (n = 21) when fever resolved before 48 h (p = 0.004).  Conclusions: During the MIS-C episode, NT-proBNP increased over time until diagnosis and treatment. It dropped faster thereafter in children with high NT-proBNP at diagnosis > 11,000 pg/mL and slower in case of persistent fever. What is Known: • NT-proBNP is useful in MIS-C for positive and differential diagnosis, diagnosis of complications and severity, and cardiogenic shock prediction. • Contrasting cut-offs for differential diagnosis and severity assessment have been suggested. What is New: • Before diagnosis, NT-proBNP increases with time and is significantly higher at 6 days from first symptoms than at 3 days suggesting different cut-offs depending on the timing of measurement. • From diagnosis and treatment initiation, the 50% NT-proBNP drop occurs earlier in children with high NT-proBNP at diagnosis > 11,000 pg/mL and later in children with persistent fever.