Hemoglobin—A Review of Structure, Mechanisms and Analysis in the Clinical Diagnostic Laboratory

This review focuses on the analysis of hemoglobin in the clinical laboratory with an emphasis on the structure–function relationships of hemoglobin and the various methodologies used for its measurement. In clinical laboratories, hemoglobin analysis may take on many forms. These include measuring the concentration of hemoglobin, as well as determining the percentage of oxyhemoglobin, deoxyhemoglobin and dyshemoglobins such as carboxyhemoglobin. There are also techniques available to estimate the oxygen affinity of hemoglobin. Hemoglobin separation techniques by means of electrophoresis or chromatography are essential in the diagnosis of hemoglobinopathies (such as sickle cell anemia) and thalassemias, where there is an imbalance in globin chain synthesis. Hemoglobin contains four globin subunits, which create a unique quaternary structure in which the oxygen affinity can be changed by allosteric modifiers, including oxygen itself. The heme iron-containing tetrapyrrole ring not only carries oxygen; it also controls the binding of oxygen to the other globin subunits. The organization and regulation of the globin genes are discussed to provide essential biological context for informed interpretation of clinical test results. Building on this foundation, selected hemoglobinopathies and thalassemias are highlighted to further illustrate structure–function relationships and their implications for diagnostic testing. However, an exhaustive analysis of hemoglobinopathies is beyond the intended scope of this review, which is not meant to be all-encompassing, as these subjects are extensively addressed in many textbooks and published articles and reviews.