Abnormal Hemoglobin Unstable Hemoglobin Few but definitions not freely available SCDO (Jade Hotchkiss) Request inclusion in the HPO, below "Abnormal Hemoglobin". Hemoglobin with decreased solubility in the red cell due to substitutions in the primary sequence of globin which alters the tertiary or quaternary structure of the molecule and results in a globin polypeptide/hemoglobin tetramer that is unstable and precipitates intracellularly, reducing the red blood cell lifespan.