What’s Your Type?

Blood clot formation and blood agglutination are two separate processes, involving different elements within the blood plasma.  Blood clotting is a mechanism the body uses to heal itself after an injury and is formed by thrombocytes (platelets) within the plasma.  After sustaining a vascular injury, platelets begin to stick to fibers near the damaged tissue as the body initiates a sequence of chemical reactions that entraps the platelets and red blood cells within a fibrin net to form a blood clot.

Figure 2 - Schematic of Maxwell model using on...
Figure 2 – Schematic of Maxwell model using one dash-pot and one spring connected in series (Photo credit: Wikipedia)

Blood agglutination occurs when the body’s natural antigens, A or B, are attacked by anti-A or anti-B antibodies respectively.  There are four types of blood and each type has either a positive or negative Rh factor; these variances come from differing antigens found on the surface of the red blood cells.  As their names imply type A blood has A antigens, type B has B antigens, AB has both A and B antigens, and type O has no antigens; the presence or absence of Rh factor determines the polarity of the blood type: if Rh antigens are present on the red blood cells the blood type is positive, if there are no Rh antigens, the blood type is negative. The antigens found on the red blood cells determine the type of antibodies found in the plasma: type A blood has anti-B antibodies whereas type B blood has anti-A antibodies.  If a type B patient receives type A blood, the anti-B antibodies in the type A plasma adhere to the B antigens on the recipient’s red blood cells, forming a cluster of red blood cells that are bound together antibody-to-antigen.

Agglutination is helpful in determining blood type in the lab, but in the human body, it can cause fatal consequences.  Both clotting and agglutination carry potentially fatal risks; however, because agglutination generally only occurs when different blood types are mixed in the body, typically via a blood transfusion in a controlled setting, the effects are monitored and treated before the condition becomes life-threatening.  Blood clots, on the other hand, are silent assassins that can cause instant death if a thrombus or embolus blocks the blood flow to or from vital organs.  If caught, clots can be treated with blood thinners and other medications; unfortunately, most often, these clots build up inside the body without any warning signs, and left untreated, can cause stroke, heart attack, and sudden death.

Thibodeau GA, Patton KT (2008). Structure and function of the body (13th Ed). St. Louis, MO: Mosby-Elsevier Inc.

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