No association of the hypercoagulable state with sickle cell disease related pulmonary hypertension.

Pulmonary hypertension (PHT) occurs in approximately 30% of adult patients with sickle cell disease (SCD) and is a risk factor for early death. Hypercoagulability has been linked to PHT in general and pulmonary artery thrombosis contributes to PHT progression regardless of its cause. Sickle cell patients are characterized by a hypercoagulable state and both autopsy and imaging studies in sickle cell patients with moderate to severe PHT suggest a role of pulmonary artery thrombosis (albeit in situ thrombosis or pulmonary embolism) in SCD-related PHT. However, in a series of 78 consecutive adult sickle cell patients, large to medium sized pulmonary artery thrombosis was ruled out with VQ scintigraphy in 25 of 26 sickle cell patients with mostly mild PHT, suggesting that pulmonary artery thrombosis is probably a late event. Nonetheless, organized thrombi in small pulmonary arteries, especially in association with obliterating vessel wall changes, may remain undetected with VQ scintigraphy. To further investigate the potential role of the hypercoagulable state in SCD related PHT sensitive markers of haemostasis were determined in sickle cell patients screened for PHT. Study design is extensively reported elsewhere. Consecutive outpatients were screened for PHT with trans-thoracic echocardiography with mild and moderate-severe PHT defined as a tricuspid regurgitant jet flow velocity (TRV) of 2.5-2.9 m/s and ≥3m/s, respectively. The study was carried out in accordance with the principles of the Declaration of Helsinki. Venous blood (3.2% citrate) was collected from the antecubital vein and platelet-poor plasma was prepared by two-step centrifugation (4000 rpm, 15 min followed by 10000 rpm, 5 min). Endogenous thrombin potential (ETP) was determined with the Calibrated Automated Thrombogram (Thrombinoscope BV, Maastricht, The Netherlands) in a 96-well plate fluorometer (Ascent Reader, Thermolabsystems OY, Helsinki, Finland). Thrombin generation was triggered with 1 pM recombinant relipidated tissue factor (rTF) and 4 μM phosphatidylserine/phosphatidylcholine/phosphatidylethanolamine vesicles in HEPESbuffered saline in presence and absence of thrombomodulin (kind gift from Prof. C. Hemker, Synapse BV, Maastricht, the Netherlands) added at a concentration that upon addition to normal pool plasma would reduce the ETP with 50%). Prothrombin fragment 1+2 (F1+2), soluble tissue factor (ELISA; Behring, Marburg, Germany), D-dimers (TintElize D-Dimer assay, Trinity Biotech, Kordia Life Sciences), and plasminogen activator inhibitor-1 activity (PAI-1:act, Chromolize, Trinity Biotech) were measured according to manufacturer’s procedures. For statistical analysis, HbSS and HbSβ-thalassemia patients were grouped together, as were HbSβ-thalassemia and HbSC patients. Between group differences were tested with the Mann-Whitney U test. For correlation studies the Spearman rank correlation coefficient (rs) was calculated. p values <0.05 were considered statistically significant (SPSS 12.0.2, SPSS Inc, Chicago, IL, USA). Of 25 PHT patients, 23 had mild PHT. Only 3 HbSC/HbSβ-thalassemia patients had PHT precluding between group statistical analysis (Table 1). No patients received blood transfusions in the weeks before study entry, use of hydroxyurea was not different between patients with or without PHT and no patients used anticoagulation, calcium antagonists, endothelin receptor blockers or sildenafil. Haematologica online only 2008