combinations of reactions shown in the table 7-1 will result.
The most important Rh factor is factor D. Approximately 85 percent of the population is D positive (also called Rh positive), and 15 percent is D negative (also called Rh negative). Aggiutinin for Rh + does not normally occur in the blood. Consequently, Rh + corpuscles do not produce reactions in first transfusions. However, the agglutinogen, when present in large amounts in the blood of recipients, may produce reactions upon transfusion with Rh + corpuscles. Consequently, it is mandatory to select compatible donors whose corpuscles are Rh for transfusion of Rh individuals. This is especially important in those who have had previous transfusions (especially with Rh + corpuscles).
Determination of the A and B agglutinogen is called grouping, while determination of the Rh agglutination is called typing (fig 7-1.) Color-coded Anti-A (blue), and anti-B (yellow), are available through the Navy Supply System.
Blood grouping for the A-B-O system is performed at room temperature. A blood specimen is drawn and allowed to clot. The erythrocytes are resuspended in the serum by mechanical agitation, and single drops are placed on a clean glass slide by a dropper. Colored specific sera are added, and each drop of blood and antiserum are individually mixed with a clean applicator stick. The preparation is observed for agglutination. If agglutination takes place, the red cells gather in clumps. If there is no agglutination, the red cells will be evenly distributed over the field (see fig. 7-1).
Table 7-1.-Agglutination Reactions of the Red Cells of the Four Blood Groups
|International Blood Group||Anti-A||Anti-B|
Denotes absence of agglutination
+ Denotes presence of agglutination
The rouleaux formation is another phenomenon that causes trouble in blood typing. It is caused by sera with high globulin content and appears as red cells stacked up like a pile of coins. Rouleaux formation can easily be confused with true agglutination. CAUTION: Droppers must be used only in their respective sera and cell suspensions to prevent cross-contamination. Applicator sticks used for mixing anti-A and the cell suspension must not be used for mixing anti-B and the cell suspension, and vice versa.
As a hospital corpsman, you need to know how to perform the tests discussed in this chapter, especially when you are on duty independent of a medical officer. Although you are not expected to diagnose or treat a patient based on the test findings, you must be able to convey a clear clinical picture to your supporting medical officer to effect prompt, efficient, and professional patient care.
It is very important that the patient, as well as the specimens received, be promptly and properly identified to prevent errors and to minimize future embarrassment and medical complications.
Another important facet of clinical laboratory is the proper use of laboratory forms. Use separate forms for each patient and each type of test. The forms must be filled out completely, accurately, and legibly to ensure expeditious disposition of completed reports. In addition, they must be properly filed and recorded.
In the laboratory you constantly will be dealing with the numerous laboratory forms associated with the tests being performed. These forms when used properly will minimize confusion and reduce chances for errors. For a complete listing of these forms and their purposes, refer to MANMED, chapter 23.
You are expected to treat all laboratory tests and their results as a confidential matter.