Negative test for HIT antibodies

Consider continuing or switching back to (LMW) heparin'

Imaging studies for lower-limb DVT

(high frequency of subclinical D\h~)

No Thrombosis

If HIT, consider anticoagulating until platelet count recovery, even if no thrombosis apparent (± coumarink)

a Recent heparin indicates exposure within the past 30 days (2 points) or past 30-100 days (1 point)

b ASR, acute systemic (anaphylactoid) reaction following Lv. heparin bolus c Stop all heparin, including low molecular weight heparin, catheter Hushes" and, possibly, heparin-coated catheters d Danaparoid: usual i.v. bolus, 2250 U (body weight 60-75 kg) followed by infusion (400 U/hr for 4 hr, then 300 U/hr for 4 hr, then 200 U/hr, adjusted by antifactor Xa levels); this therapeutic-dose regimen Is appropriate both for Isolated HIT and for HIT complicated by thrombosis; prophylactic-dose danaparoid (750 U b.i.d. or t.l.d.) appropriate when probability of HIT Is not high e Leplrudin: approved for treatment of thrombosis complicating HIT. Note that recommended dosing Is lower than package insert: 0.05-0.10 mg/kg/h adjusted to 1.5-2.5X baseline aPTTor mean of the laboratory normal range (see Chapter 14);

treat Isolated HIT (0.05-0.10 mg/kg/h, aPTT-adjusted); to avoid overdosing, it may be preferable to omit the Initial bolus, and begin with i.v. Infusion, except In patients with life- or limb-threatening thrombosis; reduce dose for renal insufficiency

1 Argatroban: approved for Isolated HIT and HIT complicated by thrombosis (2 pg/kg/min I.v., adjusted to 1.5-3.0 * patient's baseline aPTT or the mean of the laboratory normal range); reduce dose in critically ill or in heart failure (e.g., 1 pg/kg/min) and in patients with hepatobiliary compromise (0.25 pg/kg/min); increases INR more than other direct thrombin inhibitors, thus care required in managing coumarin overlap (see below)

9 Bivalirudin: no bolus, infusion 0.10 mg/kg/hr adjusted by aPTT; limited experience (off-label) h Fondaparinux: dosing for HIT not established; limited experience (off-label)

' Depending on physician confidence in the laboratory's ability to rule out HIT antibodies (usually, negative PF4-dependent enzyme-lmmunoassay and/or washed platelet activation assay performed by an experienced laboratory) ' Some thrombin may require special treatment, e.g., thrombectomy for large limb artery thrombosis k Do not begin coumarin until there is substantial recovery of platelet count (usually, >150); begin coumarin in low, maintenance doses only, with minimum 4-5 day overlap with alternative anticoagulant; stop coumarin when INR therapeutic at least 2 days

APPENDIX 12. SIX TREATMENT PRINCIPLES OF HITa TWO DO's

Do stop all heparin (including heparin flushes, low-molecular-weight heparin, etc.)b Do start an alternative, non-heparin anticoagulantc (usually in therapeutic dosesd,e)

TWO DON'Ts

Don't administer coumarin (warfarin) during the acute thrombocytopenic phase of HITf (give vitamin K if coumarin has already been given when HIT is diagnosed) Don't give prophylactic platelet transfusionsg

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