Acute Chest Syndrome (ACS) is a pulmonary complication of sickle cell disease (SCD) representing the leading cause of death and the second cause of hospitalization among adult patients. Pulmonary vaso-occlusion is one of the main pathophysiologic hypotheses during ACS. Our hypothesis is that therapeutic anticoagulation may reduce the severity of ACS via the alleviation of pulmonary thrombosis. The main objective of this prospective, randomized, double-blind study is to test the efficacy and safety of a curative anticoagulation strategy during ACS. The main efficacy endpoint is time to ACS resolution. The main safety endpoint is number of major bleedings.

A thoracic CT scan will be performed to check for pulmonary artery thrombosis. If the CT scan is positive (thrombosis within a large elastic artery), the patient will not be randomized and will be treated with a curative anticoagulation. If the CT scan is negative, the patient will be randomized to receive subcutaneous anticoagulation with low molecular weight heparin (tinzaparin) either at a curative dose (175 Unit International (UI)/kg/day for 7 days) or at a prophylactic dose (4500 UI/day).

Inclusion Criteria:

• Age ≥ 18 years
• Major sickle cell syndrome (SS, SC, Sβ)
• ACS defined by the association of a new infiltrate on chest X-ray or CT scan and a respiratory symptom or abnormal chest auscultation
• Written, informed consent

Main Exclusion Criteria:

• Pregnancy, post-partum
• Iodine allergy
• Extreme weight (<40 kg or > 100 kg)
• Moderate to severe renal insufficiency
• Moya-moya disease
• Symptomatic cerebral aneurysm
• Major transfusional risk
• Uncontrolled severe retinopathy
• All other contra-indications to curative anti-coagulation by tinzaparin.