Serum Biomarkers for Identifying Acute Chest Syndrome Among Patients Who

Objective. To compare the accuracy of biomarkers for identifying acute chest syndrome (ACS) in patients with sickle cell disease presenting to a pediatric emergency department (ED). Methods. We conducted a 13-month-long (2002–2003) cohort study with nested case-control in patients with sickle cell disease presenting to the pediatric ED with vaso-occlusive crises or fever in which we compared levels of secretory phospholipase A2 (sPLA2), endothelin-1, interleukin-6 (IL-6), and peripheral white blood cell count (WBC) in cases that were complicated by ACS and in control subjects with uncomplicated illnesses. For diagnosis, a test was considered to be accurate when the area under its receiver operator characteristic curve (AUC) was >0.70. Laboratory tests with AUC values >0.70 were entered into a binary recursive partitioning model for diagnosis. Results. For the period of study, samples from 72 visits were obtained from 51 patients who presented with vaso-occlusive crises (range: 1–4 visits per patient; 15 were enrolled more than once). ACS complicated 19 of 72 visits (26%, 95% confidence interval: 17%–38%). At an AUC value of 0.79, only the sPLA2 test was accurate for diagnosing ACS. AUC values for peripheral WBC, endothelin-1, and IL-6 were 0.68, 0.51, and 0.52, respectively. Binary recursive partitioning retained only sPLA2 at a cutoff of 13.7 ng/mL to be accurate for diagnosis. This cutoff had a sensitivity of 74% (14 of 19), a specificity of 87% (46 of 53), a positive likelihood ratio of 5.6, and a negative likelihood ratio of 0.18. Conclusions. Secretory phospholipase A2 but not endothelin-1, IL-6, or WBC is an accurate test for identifying present or incipient ACS in young patients who present to the ED with sickle cell pain crises. Pediatrics 2005;116:e420–e425. URL: www.pediatrics.org/cgi/doi/ 10.1542/peds.2004-2107; emergency medicine, sickle cell disease. ABBREVIATIONS. ACS, acute chest syndrome; SCD, sickle cell disease; VOC, vaso-occlusive crises; sPLA2, secretory phospholipase A2; IL, interleukin; ED, emergency department; WBC, white blood cell count; ROC, receiver operator characteristic; AUC, area under the curve; Sao2, oxygen saturation. Acute chest syndrome (ACS), a combination of respiratory symptoms and radiographic evidence of new pulmonary infiltrates, is the second leading cause of hospitalization in patients with sickle cell disease (SCD).1 The success of simple blood transfusions in the treatment of overt ACS is well established and raises the possibility of using such therapy earlier in the course of illness.2–4 Symptoms of impending ACS, however, may be subtle, limiting the utility of the clinical examination. In fact, a recent study reported that half of ACS cases were diagnosed after patients had been admitted to the hospital with other complaints (most commonly, vaso-occlusive crises [VOC]).2 A strategy of routine chest radiographs in patients who present with VOC may identify early cases of ACS but is undesirable because of the hazards associated with repeated exposure to radiation. Fortunately, other possibilities exist. A promising test is the level of secretory phospholipase A2 (sPLA2). In one small study, elevation of this enzyme predicted impending ACS in children with VOC.5 No attempts have been made, however, to validate these findings at other sites. Another test is the endothelin-1 level in plasma, which has been shown to rise in VOC6 but has not been evaluated for predicting ACS. Finally, peripheral blood leukocytes and interleukin (IL) levels increase in many inflammatory conditions and so may have value for detecting ACS. Among ILs, an attractive target for study is IL-6, a pleiotropic proinflammatory protein with many biologic activities that is reported to correlate positively with the number and adhesiveness of neutrophils in SCD.7,8 For now, it is not clear how these biomarkers change in response to ACS. In this study, we addressed this question. Specifically, we validated the accuracy of sPLA2 in a new setting and compared its performance with that of other tests. For ACS detection, we also defined optimal test cutoffs and evaluated a strategy that combines these tests for diagnosis.