Summary

ASH 2018 evidence-based guideline on diagnosis and management of heparin-induced thrombocytopenia (HIT), an IgG-mediated prothrombotic reaction to PF4/heparin complexes. The 33 recommendations cover platelet monitoring, use of the 4Ts score with sequential immunoassay/functional assay testing, treatment of acute HIT with non-heparin anticoagulants, and special situations (cardiac surgery, PCI, renal replacement, VTE prophylaxis, history of HIT). Novel features vs prior guidelines: an integrated diagnostic algorithm and explicit inclusion of fondaparinux and DOACs as acceptable options for acute HIT.

Key Recommendations

Use the 4Ts score (not gestalt) to estimate pretest probability of HIT in suspected cases (strong).
In low-probability 4Ts (≤3): do not order HIT laboratory testing and do not empirically discontinue heparin or start a non-heparin anticoagulant (strong).
In intermediate/high-probability 4Ts (≥4): discontinue heparin, start a non-heparin anticoagulant, and order an immunoassay; if positive, confirm with functional assay when available.
For acute HIT (with or without thrombosis): discontinue heparin and start a therapeutic-intensity non-heparin anticoagulant — argatroban, bivalirudin, danaparoid, fondaparinux, or a DOAC (rivaroxaban preferred among DOACs).
Do not start a VKA until platelet count recovery (usually ≥150 × 10⁹/L); if patient already on VKA at HIT onset, stop it and give IV vitamin K.
Do not routinely place an IVC filter or transfuse platelets in acute HIT; platelet transfusion only for active bleeding or high bleeding risk.
Screen acute isolated HIT with bilateral lower-extremity compression ultrasound; add upper-extremity ultrasound only in the limb containing a CVC.
Continue anticoagulation in isolated HIT at minimum until platelet recovery and generally not beyond 3 months; for HITT, treat 3–6 months.
In subacute HIT A, transition to a DOAC rather than a VKA.
For cardiac surgery: delay until subacute HIT B/remote HIT if possible (then use intraoperative heparin limited to surgery); if not feasible, use intraoperative bivalirudin or heparin with plasma exchange or potent antiplatelet (iloprost/tirofiban).
For PCI in acute HIT or subacute HIT A: use bivalirudin (argatroban if unavailable); in subacute HIT B/remote HIT, prefer bivalirudin over UFH.
For renal replacement therapy in acute HIT: use argatroban, danaparoid, or bivalirudin; in subacute/remote HIT not otherwise anticoagulated, use regional citrate.
Patients with history of HIT in the last 3 months should carry/wear an emergency identifier; not recommended beyond 3 months.
Monitor platelets in heparin-exposed patients only if HIT risk ≥0.1% — every other day if high risk (>1%), every 2–3 days if intermediate (0.1–1%).

Thresholds & Doses

Low HIT risk: <0.1% — no platelet monitoring
Intermediate HIT risk: 0.1–1.0% — monitor platelets every 2–3 days
High HIT risk: >1.0% — monitor platelets at least every other day
Platelet monitoring window: day 4 to day 14 (or until heparin stopped) if no heparin in prior 30 days; start day 0 if heparin within last 30 days
4Ts score: ≤3 = low probability; 4–5 = intermediate; 6–8 = high
ELISA OD ≥2.0 units = very strongly positive (functional assay may be omitted with high-probability 4Ts)
Platelet count recovery threshold: ≥150 × 10⁹/L (trigger for transitioning to VKA/DOAC oral dosing)
Argatroban: 2 µg/kg/min IV (reduce to 0.5–1.2 µg/kg/min in liver dysfunction/bilirubin >1.5, heart failure, anasarca, post-cardiac surgery); titrate to aPTT 1.5–3.0× baseline
Bivalirudin: 0.15 mg/kg/h IV (no bolus); titrate to aPTT 1.5–2.5× baseline; reduce in renal/liver dysfunction
Danaparoid bolus by weight: <60 kg 1500 U; 60–75 kg 2250 U; 75–90 kg 3000 U; >90 kg 3750 U; infusion 400 U/h ×4h → 300 U/h ×4h → 200 U/h (150 U/h if renal dysfunction); anti-Xa target 0.5–0.8 U/mL
Fondaparinux SC daily: <50 kg 5 mg; 50–100 kg 7.5 mg; >100 kg 10 mg
Rivaroxaban for HITT: 15 mg BID ×3 weeks, then 20 mg daily; for isolated HIT: 15 mg BID until platelet recovery
Apixaban for HITT: 10 mg BID ×1 week, then 5 mg BID; isolated HIT: 5 mg BID until platelet recovery
Dabigatran for HITT: 150 mg BID after ≥5 days parenteral non-heparin anticoagulant
Maximum anticoagulation duration in isolated HIT without DVT: 3 months
Emergency identifier indicated: HIT diagnosed within the last 3 months

Citations

Recommendation 1.1.a–b — platelet count monitoring by HIT risk stratum and frequency
Recommendations 2.1–2.10 and Figure 1 — 4Ts-based diagnostic algorithm with immunoassay/functional assay sequencing
Recommendation 3.1 and Table 2 — non-heparin anticoagulant choices and dosing for acute HIT
Recommendations 3.4–3.6 — against routine IVC filter, against VKA before platelet recovery, against routine platelet transfusion
Recommendations 3.7–3.8 — ultrasound screening for DVT and duration of anticoagulation in isolated HIT
Recommendation 3.9 — DOAC preferred over VKA in subacute HIT A
Recommendations 4.1–4.2 — cardiovascular surgery management by HIT phase
Recommendations 5.1–5.2 — bivalirudin for PCI; Recommendations 6.1–6.2 — RRT anticoagulation; Recommendations 7.1 and 8.1 — VTE prophylaxis in remote HIT and emergency identifier