An observational study in Sickle Cell Disease, Venous Thrombosis and Sickle Cell Trait, sponsored by National Heart, Lung, and Blood Institute (NHLBI). Completed at 1 site in United States. Open to participants aged 18 Years to 80 Years. Per ClinicalTrials.gov, last updated 2026-06-12.
Sponsored by National Heart, Lung, and Blood Institute (NHLBI) · Observational
Background:
Venous thromboembolism (VTE) includes the abnormal clotting of blood in a deep vein of the upper or lower limbs (deep vein thrombosis) that may travel to and block a blood vessel in the lung (pulmonary embolism). Some people with sickle cell disease (SCD)-a red blood cell disorder-seem to be at greater risk for developing these blood clots. Researchers want to study the blood of people with SCD and VTE as well as healthy people to develop better treatments to prevent blood clots.
Objective:
To study blood clotting in SCD because it is the most common cause of vascular death after a heart attack or stroke.
Eligibility:
People ages 18-80 who have SCD (with or without a history of blood clots) or the trait for SCD, and healthy volunteers
Design:
Participants will be screened with medical history, physical exam, and medical records review. They will give blood samples.
Participants will have phone calls either every 3 months or once a year, for 2 years. They will give updates on their health. They may give additional medical records. The phone calls may last up to 30 minutes.
If participants have a VTE or pain crisis episode, they may visit the Clinical Center. These visits may last up to 4 hours. They will repeat the screening tests and give blood samples.
Some participants may be invited to take part in blood studies.
After 2 years, some participants will have a follow-up visit at the Clinical Center.
Participation will last for about 2 years.
Venous thromboembolism (VTE) the third most frequent cause of vascular mortality after myocardial infarction and stroke, occurs more frequently among Americans of African descent compared with other ethnic minorities in the US. VTEs are provoked by diverse risk factors but can be unprovoked in individuals with a hypercoagulable state, in whom there is a predisposition for thrombosis. Patients with Sickle Cell Disease (SCD) have added risk of VTE as the disease itself is a hypercoagulable state. VTE frequency is increased across the entire spectrum of SCD severity, in those experiencing both mild (HbSC patients) and severe sickling symptoms (HbSS/HbSbeta0 thalassemia patients). Studies show that up to 12% of patients with SCD have VTE events [deep vein thrombus (DVT) or pulmonary embolism (PE) or both] early in life by age 40, most of which are unprovoked. Moreover, owing to a persistent hypercoagulable state, SCD patients are at an unacceptably high risk for recurrence, particularly those in whom VTE was unprovoked. SCD patients who develop a VTE have a 24.1% risk of recurrence over 5 years. A history of a VTE in SCD is associated with greater mortality risk (Odd Ratio, OR = 2.88; Confidence Interval, CI = 2.35 - 3.52).
Our overall hypothesis is that the proinflammatory state associated with SCD perturbs the coagulation system and contributes to the thrombotic vascular pathobiology of SCD. Abnormal intravascular tissue factor expressed on monocytes and endothelial cells and circulating tissue factor positive extracellular vesicles released by these cells drive coagulation activation in SCD. Specifically, intravascular tissue factor forms the tenase complex (TF:VIIa) which converts factor X to factor Xa, generating the initial thrombin burst that possibly triggers intravascular thrombosis. Besides, heightened tissue factor exposure during acute sickling crises, increased release of tissue factor positive extracellular vesicles and inadequate clearance of the latter favors thrombin generation, fibrin deposition and thrombosis in the venous vasculature. SCD patients with VTE and/or recurrent VTE are therefore more likely to have more tissue factor positive extracellular vesicles and plasma tissue factor procoagulant activity compared with SCD patients without VTE.
Prospective cohort studies of extended duration/indefinite anticoagulation in non-SCD patients with an underlying hypercoagulable state have effectively reduced recurrence rates. However, similar studies of extended duration anticoagulation in SCD patients are lacking. Besides, whether exposing SCD patients to extended/indefinite anticoagulation increases bleeding risk to unacceptably high levels is unknown. Studying thrombogenic risk and specifically identifying those SCD patients who are at greatest risk for VTE recurrence therefore becomes a high priority. In addition, individuals with sickle cell trait are prone to thrombosis but few studies evaluate markers of thrombotic risk in these individuals. Such studies could provide a rationale for targeted primary or secondary VTE prophylaxis.
In the current proposal we will test the hypothesis that plasma tissue factor positive extracellular vesicles and tissue factor activity are elevated among SCD patients with VTE compared with SCD patients without VTE and in individuals with Sickle Cell Trait compared with ethnically matched controls.
43 studies on the registry are indexed under Sickle Cell Trait; 11 are open to participants now.
This study's enrollment of 119 is close to the median of 109 across 20 observational studies indexed under Sickle Cell Trait.
Browse Sickle Cell Trait studies →National Heart, Lung, and Blood Institute (NHLBI) is the lead sponsor of 1,143 studies on the registry; 71 are open to participants now.
Of its 58 completed or terminated interventional studies of FDA-regulated products, 51 (88%) have results posted.
Compared within Sickle Cell Trait, this study's primary condition as ClinicalTrials.gg classifies it; the registry's first condition term is Anemia, Sickle Cell. The counts are of registry records indexed under each term, refreshed daily. How we classify →
The natural history of SCD 04-H-0161 protocol (NCT00081523) will specifically be leveraged to recruit participants with VTE. In this study we will assess feasibility of establishing a prospective natural history study of thrombosis in SCD. Establishing feasibility could lead to recruitment of SCD patients experiencing thrombosis, particularly those that are understudied including patients with HbSC disease.
Go through the criteria one by one — yes, no or not sure — and take the list to your doctor or the study team. Kept in this browser only.
Sickle cell disease with and without VTE
Sickle cell trait
Ethnically matched controls
EXCLUSION CRITERIA:
SCD with and without VTE
SCT and ethnically matched controls
Underlined terms in the criteria open these too. Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Hepatitis B is a virus that infects the liver. These are separate tests: HBsAg positive usually means a current infection (a recent vaccination can briefly cause it too); total anti-HBc (HBcAb) positive means an infection now or in the past; HBV DNA measures how much virus is in the blood.
Some studies accept a past infection if HBV DNA is undetectable, sometimes with antiviral medicine during the study. Check what this study allows.
Hepatitis C is a virus that infects the liver. An HCV antibody test can stay positive after an infection has cleared (and is occasionally positive without one); an HCV RNA test shows whether the virus is there now.
After treatment, hepatitis C counts as cured when HCV RNA is still undetectable 12 weeks or more after the treatment ended. Studies often accept people cured this way.
The human immunodeficiency virus, which weakens the immune system.
Many studies now accept people whose HIV is controlled on treatment, judged by the viral load and the CD4 count. Check the limits this study sets.
Hepatitis B tests
Hepatitis B is a virus that infects the liver. These are separate tests: HBsAg positive usually means a current infection (a recent vaccination can briefly cause it too); total anti-HBc (HBcAb) positive means an infection now or in the past; HBV DNA measures how much virus is in the blood.
Some studies accept a past infection if HBV DNA is undetectable, sometimes with antiviral medicine during the study. Check what this study allows.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Hepatitis C tests
Hepatitis C is a virus that infects the liver. An HCV antibody test can stay positive after an infection has cleared (and is occasionally positive without one); an HCV RNA test shows whether the virus is there now.
After treatment, hepatitis C counts as cured when HCV RNA is still undetectable 12 weeks or more after the treatment ended. Studies often accept people cured this way.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
HIV
The human immunodeficiency virus, which weakens the immune system.
Many studies now accept people whose HIV is controlled on treatment, judged by the viral load and the CD4 count. Check the limits this study sets.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
50 Men and Women with sickle cell disease and VTE
50 Men and Women with sickle cell disease but no VTE
50 Men and Women with sickle cell trait
50 ethnically matched Men and Women without sickle cell disease, sickle cell trait, or VTE
tissue factor positive
Number of tissue factor positive EVs/ml of plasma
Time frame: At baseline during study
PDFs hosted by the registry, ClinicalTrials.gov.
Plan to share: Undecided — Undecided: It is not yet known if there will be a plan to make IPD available
Ran from Sep 2020 to primary completion in Jun 2024, 45 months.
How these figures are worked out, and which studies are left out of them.
This study is completed, as verified in Jun 2026. You cannot join it, but the record below documents what was studied.
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National Heart, Lung, and Blood Institute (NHLBI) →