SCD is an inherited blood disorder, and symptoms include anemia, infections, organ damage, and intense episodes of pain, which are called "sickle cell crises." ACS, characterized by fever, respiratory distress, and lung tissue damage, is the second most common cause of hospitalization and the leading cause of death among people with SCD. Most people with SCD will experience at least one episode of ACS, and repeated episodes can result in progressive lung disease. ACS can appear suddenly and often requires immediate hospitalization and treatment, which can include blood transfusions. People with elevated blood levels of sPLA2 may be at risk for developing ACS, and this enzyme is often detectable before the onset of ACS symptoms. The purpose of this study is to examine the use of sPLA2 as a predictor of ACS and to determine whether subsequent blood transfusions can be administered early enough to prevent the onset of ACS in people with SCD who are at risk for ACS. Study researchers will also assess the feasibility of conducting a larger study that would further examine the effectiveness of using sPLA2 levels and blood transfusions to prevent ACS.