Graded Agglutination Reactions
المؤلف:
Mary Louise Turgeon
المصدر:
Immunology & Serology in Laboratory Medicine
الجزء والصفحة:
5th E, P144-145
2025-07-15
495
Observation of agglutination is initially made by gently shaking the test tube containing the serum and cells and viewing the lower portion, the button, with a magnifying glass as it is dispersed. Because agglutination is a reversible reaction, the test tube must be treated delicately, and hard shaking must be avoided; however, all the cells in the button must be resus pended before an accurate observation can be determined. Attention should also be given to whether discoloration of the fluid above the cells, the supernatant, is present. Rupture or hemolysis of erythrocytes is as important a finding as agglutination.
The strength of agglutination (Table 1; Fig. 1), called grading, uses a scale of 0, or negative (no agglutination), to 41 (all erythrocytes clumped). Table 2 describes false-positive and false-negative reactions. Pseudoagglutination, or the false appearance of clumping, may rarely occur because of rouleaux formation. Rouleaux formation can be encountered in patients with high or abnormal types of globulins in their blood, such as in multiple myeloma or after receiving dextran as a plasma expander. On microscopic examination, the erythrocytes appear as rolls resembling stacks of coins. To disperse the pseudoagglutination, a few drops of physiologic NaCl (saline) can be added to the reaction tube, remixed, and reexamined. This procedure, saline replacement, should be per formed carefully after pseudoagglutination is suspected. It should never be done before the initial testing protocol is followed; a false-negative result may occur from the dilutional effect of the saline.
Table1. Grading Agglutination Reactions
Fig1. Reading red blood cell agglutination reactions. (From Lehman CA: Saunders manual of clinical laboratory science, Philadelphia, 1998, Saunders, pp 394-395.)
Table2. Causes of False-Positive and False Negative Agglutination Test Reactions
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