Hemoglobin
As a component of blood, hemoglobin can be an important facet of a forensic investigation, especially to help detect the illegal practice known as "blood doping" in sports, and in helping to identify if a blood sample was from someone with a blood abnormality such as sickle cell disease.
Hemoglobin is a protein formed of two subunits (alpha and beta) that is found in red blood cells. The protein functions to pick up oxygen and distribute it throughout the body.
Both the alpha and beta subunits need to be present for the acquisition of oxygen, as does an iron molecule. Indeed, it is the presence of the iron that gives red blood cells the distinctive color that inspired their name.
The presence of iron enables hemoglobin to alternatively bind oxygen and carbon dioxide. As blood is pumped through the myriad of tiny channels that permeate the lung, oxygen can diffuse across the membrane of the channel to the red blood cell-containing fluid within the channels. There, the binding of oxygen to the iron-containing hemoglobin occurs. The oxygenated red blood cells pass out of the lungs and circulate throughout the body, transporting the oxygen along with them to cells.
Once oxygen has been released from hemoglobin, the vacated binding site is able to bind carbon dioxide and other waste products of cellular metabolism. This process is vital to maintain a body in a proper equilibrium. If otherwise allowed to accumulate, these products would reach toxic concentrations. The hemoglobin bound carbon dioxide is transported back to the lungs, where it is released from the red blood cells and expired. Completing the
cycle, the once-aging vacant iron site can bind another molecule of oxygen.
The alpha and beta subunits of hemoglobin are encoded by separate genes. Normally, an individual has four alpha-encoding genes and two beta-encoding genes. Despite the different number of genes, protein production is coordinated so that precisely equal amounts of the subunits are made during red blood cell manufacture. The subunits are incorporated into the developing blood cells, where they remain throughout the days-to-weeks lifespan of the cells.
In the majority of people, both hemoglobin itself and the genes encoding the subunits are invariant. This aspect would seemingly rule out the routine use of hemoglobin as a tool to identify someone in a forensic investigation. However, in people with sickle cell disease (in which the abnormally-shaped red blood cell cannot easily pass through all blood vessels, producing an oxygen shortage) and thalassemia (a group of related maladies, in which hemoglobin production is low) the mutated hemoglobin gene that is the root of the malady can be detected in now-routine molecular biological test procedures such as gene sequencing (where the order of the bases that make up a gene is determined).
If a blood sample recovered from the investigation scene contains a mutated hemoglobin gene, the discovery of the same mutation in a blood sample of a suspect, for example, can be powerful, although not unequivocal, evidence tying the suspect to the crime scene.
In addition to the well-known hemoglobin disorders that underlie sickle cell anemia and thalassemia, there are several hundred other forms of abnormal hemoglobin. These forms, which usually do not cause harm to a person, can be detected using specialized molecular examination techniques, and so can be useful forensically.
In the case of a bloodstain at a crime or accident scene, determination of the amount of hemoglobin can be useful in indicating the approximate age of a person as well as their sex. Hemoglobin content can be determined in a less sophisticated fashion than hemoglobin disorders. Blood cells are broken apart in automated blood analyzers to free the hemoglobin. Upon exposure to a cyanide-containing compound, free hemoglobin binds the cyanide. The resulting compound (cyanmethemoglobin) specifically absorbs light at a wavelength of 540 nanometers, permitting the amount of hemoglobin to be determined. Normal ranges for hemoglobin (expressed as grams per deciliter; a deciliter being 100 milliliters) are 17–22 for newborns, 11–13 for children, 14–18 for adult males and 12–16 for adult females, as a few examples. While not by itself definitive, hemoglobin content determinations of a blood sample can be another useful piece of forensic evidence.
When hemoglobin levels in blood or the red blood cells are low, as in the aforementioned cases of sickle cell anemia and thalassemia, an individual is described as being anemic. Anemia can also arise from loss of blood in a traumatic injury or internal blood loss, a nutritional deficiency, or compromised bone marrow. Thus, hemoglobin analysis can provide clues concerning the health of a victim or suspect.
Higher than normal levels of hemoglobin can be encountered in people who routinely live or work at high altitude, due to the increased production of red blood cells to maximize the blood's oxygen carrying capacity. Athletes who have artificially increased this capacity through blood doping by infusing their own previously collected red blood cells, or injecting the drug erythropoetin, which triggers the body to increase its red blood cell supply, can be found out in this way.
