2 Heparin and Low-Molecular-Weight Heparins

Uses and administration

Unfractionated heparin (UFH) and low-molecular-weight heparins (LMWHs) are anticoagulants used to prevent or treat blood clots. Common purposes include preventing venous thromboembolism in at-risk patients and treating deep-vein thrombosis or pulmonary embolism. Heparin products are also used in certain acute coronary and procedural settings, depending on the product and clinical indication.

Routes and administration precautions

UFH is commonly given intravenously or subcutaneously. LMWHs, such as enoxaparin, are usually given subcutaneously. Use the prescribed route and dose, and follow the specific product’s injection instructions and clinical protocol. Neither UFH nor LMWH is given orally; subcutaneous heparin should not be administered intramuscularly.

Baseline and ongoing safety checks

Before treatment, check baseline blood counts, including platelets, and relevant coagulation tests. Assess kidney function where relevant, particularly when using LMWH. During treatment, monitor for bleeding and follow platelet counts and other tests as appropriate to the drug, dose, patient, and local protocol.

Monitoring UFH

For a continuous UFH infusion, dosing is commonly adjusted using aPTT or an anti-factor Xa assay calibrated for UFH, according to the institution’s protocol. Coagulation testing is recommended during full-dose UFH therapy. UFH infusion monitoring commonly includes serial aPTT or anti-factor Xa testing.

Monitoring enoxaparin

Routine coagulation-test adjustment is generally unnecessary for enoxaparin. PT/INR and aPTT are not adequate tests for monitoring its anticoagulant effect. Anti-factor Xa measurement may be considered in selected situations, such as renal impairment or when abnormal coagulation results or bleeding raise concern. CBC, including platelets, and clinical signs of bleeding should also be monitored.

Recognizing and responding to bleeding

Black stools and dizziness during heparin treatment raise concern for clinically important bleeding, potentially gastrointestinal hemorrhage. Promptly notify the treating clinician and assess the patient. Further management depends on the severity, hemodynamic status, and anticoagulant exposure; these symptoms should not be dismissed as expected effects.

Suspecting and responding to HIT

A substantial platelet fall together with a new thrombosis during heparin treatment raises concern for HIT with thrombosis (HITT). For example, a fall from $\mathrm{240{,}000\ cells\,\mu L^{-1}}$ to $\mathrm{105{,}000\ cells\,\mu L^{-1}}$ on day 7 with a newly identified thrombosis is concerning. HIT is dangerous because thrombosis can occur despite a low platelet count.

Use the 4Ts score to estimate clinical probability. It assesses the degree of thrombocytopenia, timing of the platelet fall, thrombosis or other HIT-related consequences, and other possible causes of thrombocytopenia. A structured score is recommended rather than clinical impression alone.

With intermediate or high suspicion, stop all heparin exposure, including heparin flushes, and urgently evaluate for HIT. Management generally requires a non-heparin anticoagulant while diagnostic testing proceeds, guided by the clinical situation and bleeding risk.

Reversal

Protamine can reverse UFH. It only partially reverses enoxaparin’s anticoagulant effect, so reversal and bleeding management require clinical assessment.