(2) Variation in the strength of the antigen. Some antigens that do not show
dosage in terms of zygosity may vary in strength on cells from different individuals. The
antigens most notable for this are P1, Sda, Lea, Leb, and I. Sometimes diminished
antigenic strength can be related to disease, or to the length of time that the cell
suspension has been stored.
1-38. COLD ANTIBODIES
a. Background. These antibodies react best at room temperature (RT) and
below, while reactions after 37C incubation and with AGT are negative or weakly
positive. Some cold agglutinating antibodies, notably anti-I, anti-lH, and anti-H, bind
complement following the antigen-antibody interaction at low temperatures; subsequent
37C incubation may cause the antibody to elute from the cell, but the attached
complement remains, and produces a positive reaction when antiglobulin serum is
added. An antibody displaying these characteristics in the screening test or in
crossmatches should be tested at 18C and/or 4C with specially selected cells, such as
b. Cold Autoabsorption to Remove Cold-Reactive Autoantibody.
(1) When a strong, cold, autoantibody is present, meaningful
antibody-screening and compatibility studies cannot be done until the autoantibody is
removed. This can be done with the patient's untreated or enzyme-treated cells.
Enzyme pretreatment results in faster antibody removal, and is more effective with very
high-titered autoantibodies. Untreated autoabsorption is usually satisfactory for
removing low-level activity.
(2) Some alloantibody may also be removed by the Matuhasi-Ogata
phenomenon, or by transfused cells in the circulation. In recently transfused patients,
when autoabsorption might result in removing alloantibody activity, the
antibody-screening test and compatibility tests should be done at 37C, using serum
from a blood sample clotted at 37C and kept at that temperature until the serum is
removed. This permits detection of antibodies active at 37C, and by AGT, but not
(a) STEP 1. Obtain a blood specimen from the patient. At the bedside
draw two specimens of blood, one in a tube immediately placed in ice, the other in a
tube containing anticoagulant and incubate it at once at 37C. To do this, bring a
heated block, water bath, or vacuum jug of 37C water to the patient's bedside. The
tube may also be transported in an inside pocket.
(b) STEP 2. Allow the first (iced) specimen to clot in the refrigerator.
Separate the serum by centrifuging in ice-filled cups or a refrigerated centrifuge.
Immediately remove the serum from the clot.