Efficiency of RBC Antibody Detection Methods: Comparison of Manual Indirect Antiglobulin Test (IAT) to a Method Using Very Low Ionic Strength Conditions (vLIS/IAT).

Abstract 2276

Is has long been known that RBC antibody detection is enhanced following a decrease in the ionic concentration. In the past we added into our routine pre-transfusion antibody screen a new test, which employs ionic strength conditions between 15 to 17% of the ionic strength of 0.9% NaCl (vLIS/IAT): 2 drops of patient's plasma and one drop of 3% RBC are incubated for 15 minutes in 0.5 mL of 5% mannitol, pH 6.0 with phosphate buffer, containing 8mM EDTA. The RBCs are washed with normal saline and tested for agglutination by an anti-IgG reagent. Other published low ionic strength methods decrease the ionic concentration less, up to about 50%.

In the process of pre-transfusion testing we found 711 patients with one, two or more blood group antibodies. The following table shows the specificities and quantities of clinically significant antibodies detected by these two methods. The following antibody specificities were not included: those that were present only in small quantities, directly agglutinating IgM antibodies and anti-Le^a and Le^bantibodies which are usually considered to be clinically insignificant.

Overall, vLIS/IAT detected an increase in clinically relevant antibodies compared to IAT. This is clearly seen in the case of anti-E, anti-D, anti-Jk^a, anti-M and anti-S antibodies. Anti-K antibodies, however, were detected preferably by IAT. It should be noted that more anti-Le antibodies, although not shown here, were detected either by IAT or by direct agglutination (IgM antibodies).

In summary, these data show that vLIS/IAT improved antibody detection when incorporated into routine pre-transfusion tests. They also indicate that one method does not detect all clinically significant antibodies; therefore it is beneficial to use two methods which in combination cover the varying spectra of RBC antibodies.