Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (298 page)

   Bilirubin gallstones are present in 30% of patients by age 18 and 70% by age 30.

   Organ damage develops by the time SCA patients are in their teens, with the lungs, kidneys, heart, and liver involvement. Cerebrovascular accidents are also common.

   Laboratory Findings

   A “sickle cell screen” can be obtained for a rapid preliminary diagnosis. It is positive in SCA, SCT, in some
non-S sickling
hemoglobinopathies, and in combined SCD with other hemoglobinopathies.

   Hb variant analysis (HPLC or electrophoresis) is used to identify different hemoglobins. Newborns have predominantly HbF with a small amount of HbS and no HbA1. Because other sickle cell syndromes may have similar patterns, it is recommended to study the parents, or repeat the test after 1 year of age, when the adult pattern of SCA is established: very high HbS. HbF may be slightly elevated (1–4%) and especially in patients treated successfully with hydroxyurea where it may reach 15% or more, resulting in marked diminution in morbidity.

   The newborn with SCT will have HbA, HbF, and HbS. Adults have >50% HbA1 and 35–45% HbS.

   Prenatal testing: gene analysis of fetal DNA may be performed on chorionic villi (7–10 weeks of gestation) or amniocytes (15–20 weeks of gestation). DNA testing may be also useful in newborns or children in cases with high levels of HbF if hereditary persistence of fetal hemoglobin is suspected.

   Patients with HbSC disease (see below) have equal amount of HbS and C.

   Patients with sickle cell trait–β-thalassemia (+) have HbA1, elevated HbA2, and HbS.

   
CBC
in patients with SCA.

   RBC: mild to moderate chronic hemolytic anemia (Hct 15–30%, Hb 5–10 g/dL), punctuated by aplastic crises (sudden, life-threatening episodes of very severe anemia) (see above).

   Reticulocytes 3–15% (they may account for an elevated MCV).

   MCV is in general normal (except as noted above); MCHC is elevated. Microcytosis and hypochromia may be present, however, if there is coexisting α- or β-thalassemia, or iron deficiency in nontransfused patients.