Studies evaluating interlaboratory agreement in the monitoring of heparin have failed to show that corre- lating the aPTT with anti-Xa assays improves agree- ment between hospital laboratories,84,85 re ecting, at Table 3 Example of a Heparin Dose Adjustment Nomogram Initial dose 80 units/kg bolus, then 18 units/kg/h aPTT,,35 s 80 units/kg bolus, then increase 4 units/kg/h aPTT, 35-45 s 40 units/kg bolus, then increase 2 units/kg/h aPTT, 46-70 sa No change aPTT, 71-90 s Decrease infusion rate by 2 units/kg/h aPTT,.90 s Hold infusion 1 h, then decrease infusion rate by 3 units/kg/h aPTT5activated partial thromboplastin time. (Adapted with permis- sion from Raschke et al.65) aTherapeutic aPTT range of 46-70 s corresponded to anti-Xa activity of 0.3-0.7 units/mL. The target aPTT range in a particular institution should re ect what is known about the local reagents and equipment used to perform the assay. 2012 American College of Chest Physicians by Kimberly Henricks on February 10, 2012 chestjournal.chestpubs.org Downloaded from www.chestpubs.org CHEST / 141 / 2 / FEBRUARY, 2012 SUPPLEMENT e29S Patients who have previously received protamine sulfate-containing insulin, have undergone vasec- tomy, or have known sensitivity to sh are at increased risk to have preformed antibodies against protamine sulfate and to suffer from allergic reactions, including anaphylaxis.100,101 Such reactions are uncommon, but if there is concern about a potential protamine sulfate allergy, patients can be pretreated with corticoste- roids and antihistamines. A number of other substances or devices have been shown to neutralize the anticoagulant effects of UFH. These include hexadimethrine (Polybrene),102,103 heparin removal devices,107 and synthetic protamine variants.108 None of these is approved for clinical use. 1.2 Low-Molecular-Weight Heparins LMWHs are derived from UFH by chemical or enzymatic depolymerization. 