What is Known: • Published recommendations on research blood sampling in children are heterogeneous; European recommendations propose ≤ 1% of total blood volume at a single time point and ≤ 3% over 4 weeks. • Evidence supporting these thresholds is limited.

What is New: • This review translates these recommendations into a practical framework: a weight-based reference table, rolling 4-week tracking of research blood loss alongside clinical sampling, and coordination between clinical and research teams. • It summarises residual-sample and microsampling strategies, including their limitations.