Test code links throughout this Guide refer to the corresponding test in the User's Guide. Internal bonding forces of hemoglobin are thus weakened, predisposing to precipitation. Unstable hemoglobins precipitate faster than normal hemoglobin.
Most patients are heterozygous for the defective hemoglobin gene.
These hemoglobinopathies differ from thalassemias in that they result from structural chain abnormalities rather than from deficiencies in chain number. As Heinz bodies are removed in the spleen, membrane is damaged and lost, leading to decreased red cell survival. A positive test is indicative of an abnormal hemoglobin if sickle hemoglobin, fetal hemoglobin, and methemoglobin can be excluded. Normal hemoglobin does not precipitate until incubation has extended 30-40 minutes. Unstable hemoglobins precipitate within 20 minutes, and often in 5 minutes or less.