THE APTT MONITORING OF HEPARIN - THE ISTH ICSH COLLABORATIVE STUDY

In an international collaborative study. three candidate reference and the local APTT reagent have been tested with lyophilized plasmas cont aining heparin added in vitro and fresh plasmas from heparinized patie nts to determine whether it was possible to standardize APTT heparin m onitoring. The APTT responses of patients with thrombosis were much le ss to the same concentrations of heparin so only these plasmas were us ed to calibrate the reagents. A calibration constant (b) was determine d for each local APTT system from the orthogonal regression slope of t he patients' and normals' plasmas. Although the calibration was based on relatively limited numbers of patients' plasmas the results gave no consistent indication that this method of analysis with the reference preparations was incorrect. Two of the three candidate reference reag ents performed almost equally well and one of these reagents is recomm ended as the APTT reference preparation. Use of a single b value for a brand of reagent for all laboratories is not advised. Each laboratory must perform its own local calibration. The adoption of a reference A PTT reagent together with the use of orthogonal regression analysis wo uld be a useful step to initiate APTT heparin monitoring standardizati on and to develop safe and effective local therapeutic ranges.