Common and Severe Complications of Sickle Cell Disease

    A doctor and patient talking, the doctor holding a prescription bottle that he's pointing toA team of scientists with the National Heart, Lung, and Blood Institute (NHLBI) of the National Institutes of Health has found that a hormone detected in a simple blood test can identify patients with sickle cell disease who have developed a life-threatening complication called pulmonary hypertension. The team has also found that the same hormone is a clear predictor of death in adult sickle cell patients.

    The hormone, called brain natriuretic peptide or BNP, is released
    by the heart ventricles and helps predict death in heart failure patients. The
    new study is published in the July 19 issue of the Journal of the American
    Medical Association.

    “This is an important leap forward in research on sickle cell
    disease,” said NHLBI Director Elizabeth G. Nabel, M.D. “Having a marker in the blood that will not only help identify sickle cell patients with this deadly complication but also predict those at the highest risk — will aid in the care and treatment of these patients.”

    Sickle cell anemia is one of the most common genetic blood disorders in the United States. About 30 percent of sickle cell patients have pulmonary hypertension. In this condition, there is constant high blood pressure in the pulmonary arteries that supply the lungs. This pressure leads to narrowed arteries, causing the heart to work harder to pump blood.

    Pulmonary hypertension often leads to heart failure and it is a major risk factor for death in adults with sickle cell disease. Currently, echocardiograms and other heart tests are used to diagnose pulmonary hypertension, but there has not been a blood test to help detect the condition.

    Previous research has found that in patients with pulmonary hypertension, higher levels of BNP are associated with greater pressure in the pulmonary arteries. NHLBI researchers theorized that BNP levels might also correlate with the severity of pulmonary hypertension and risk of death in sickle cell patients.

    Lead scientist Roberto Machado, M.D., an investigator with NHLBI’s
    Vascular Medicine Branch, and colleagues measured BNP levels in 230 patients with sickle cell disease enrolled in the NIH Pulmonary Hypertension Screening Study between 2001 and 2005. In order to confirm a diagnosis of pulmonary hypertension, the patients were given echocardiograms and other measurements of heart function. BNP levels were also measured in 45 healthy black controls, since the disease is more prevalent in blacks.

    The scientists found that high blood levels of BNP — greater than 160 pg/mL — in these patients independently predicted mortality, increasing the risk of death by as high as fivefold.

    The team also found that BNP levels could help identify the patients with pulmonary hypertension. NIH study patients who had a BNP of 160 pg/mL or higher had a 78 percent chance of having pulmonary hypertension
    identified by echocardiogram.

    “We now have another tool to help diagnose pulmonary hypertension,” Machado said. “There is tremendous value in diagnosing this deadly complication early and accurately so we can aggressively treat the complication and try to improve the patient’s outcome.”

    To validate and confirm the findings, the team then measured BNP
    levels in 121 stored blood samples from patients who had been enrolled in a
    sickle cell drug treatment study, the Multicenter Study of Hydroxyurea in Sickle Cell Anemia (MSH) Follow-up Study which began in 1996. These patients came from major sickle cell centers around the United States and at the time of enrollment it was not known that pulmonary hypertension was a common complication of sickle cell disease.

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