Problems in laboratory monitoring of heparin dosage

1. The anticoagulant of choice for monitoring UFH therapy is CTAD (Van den Besselaar et al. 1987). 2. Samples should be collected 4-6 h after initiation on infusion, injection or dose adjustment (Olson et al, 1998). 3. When employing APTT for monitoring UFH, the responsiveness of the monitoring system must be taken into account when recommending a therapeutic range (Brill-Edwards et al, 1993; Kitchen & Preston, 1996), and should correspond to 0.2-0.4 units/ml by protamine titration or 0.35-0.7 units/ml by anti-Xa assay (Hirsh, 1991). 4. The heparin level can be used for monitoring UFH, particularly when APTT is inappropriate (Levine et al, 1994). 5. Clinically stable patients receiving LMWH as DVT prophylaxis or uncomplicated patients treated for venous thromboembolism by a weight-adjusted fixed dose, do not require laboratory monitoring (Laposata et al, 1998). 6. LMWH may require monitoring in selected cases such as renal insufficiency, prolonged therapy including pregnancy, paediatric patients, those at high risk of bleeding or thrombotic recurrence, and patients with obesity or low body-weight (Laposata et al, 1998). 7. A target therapeutic range of 0.5-1.1 iu/ml has been recommended for patients receiving twice daily LMWH therapy (Laposata et al, 1998). 8. Anti-Xa-activity assays for LMWH should be calibrated using a material itself calibrated against the International Standard for LMWH. 9. Results of anti-Xa assays may vary according to the technique employed (Kitchen et al, 1999b).