Use

This assay measures heparin levels by detecting inhibition of factor Xa via the heparin‑antithrombin III complex using a chromogenic substrate. It is calibrated to both unfractionated heparin (UFH) and low molecular weight heparin (LMWH), allowing monitoring of either therapy. Peak anti‑Xa levels for LMWH dosing (e.g., enoxaparin 1 mg/kg q12h) are typically 0.5–1 IU/mL; for q24h dosing of LMWHs (e.g., enoxaparin 1.5 mg/kg q24h), levels are 1–2 IU/mL, sampled approximately 4 hours post‑dose after steady state. UFH monitoring timing depends on local hospital protocols, often ~6 hours after dosage change, recognizing potential delays when samples are sent to Quest laboratories.