George recommends the April CAP Today article, Hemophilia Management, Tips on Monitoring Modified Replacement Therapies. The article, featuring Stefan Tiefenbacher, PhD, of Colorado Coagulation, and Rajiv K. Pruthi, MBBS, of Mayo Labs, describes the newly approved extended half-life coagulation factor VIII and IX concentrates. Hemophilic boys are delighted to reduce the frequency of infusions, however the pharmacokinetics of the factors vary by patient. Further, the formulations include various combinations of B-domain deletion, PEGylation or Fc fragment fusion. Consequently, laboratory monitoring is essential to established individualized dosage patterns, but regrettably, our time-honored clot-based, one-stage factor assay approach provides inadequate recovery, both under- and over-estimating circulating plasma factor levels. Results are affected by factor concentrate formulation and by reagent characterisitics, especially the activators, be they silica, kaolin, or ellagic acid. What approach are you using? Please comment below.