Techniques for Emergency Compatibility Testing MLS 522

Introduction A crossmatch is the final part of the process which determines the compatibility of donor red cells with the patient. This may be serological or electronic. Selection and issue of red cells and other blood products are inherently high risk procedures and all care should be taken to reduce the risk. The transfusion of ABO-incompatible blood is now classed as a “never event”.

Introduction Safety of transfusion begins with proper collection of the sample. It has been estimated that 1 in 2000 samples is from the wrong patient, commonly known as “wrong blood in tube” and this continues to be a serious problem. The use of secure bedside electronic patient identification systems reduces this risk. However in the absence of such systems, it is highly recommended that a second sample is requested for confirmation of the ABO group of a first time patient.

Crossmatching Guidelines Provided it does not impede the delivery of urgent red cells or other components. Whatever crossmatching procedure or technique is used, it should be capable of detecting an ABO incompatibility. Urgent need for transfusion may preclude the performance of usual testing protocol.

In urgent situations, the attending physician must weigh the risk of transfusing uncrossmatched or partially crossmatched blood against the risk of delaying transfusion. And depriving the patient of oxygen- carrying capacity until testing is completed. In some severe cases, transfusion of incompletely tested blood is always preferable to the risks associated with a rapidly dropping hemoglobin.

Crossmatching Guidelines(contd) Antibody screening can be undertaken in advance of the requirement to provide blood for transfusion (in non- emergency cases). This alerts the clinician to possible delay in the supply of compatible blood if the antibody screen is positive. It also provides the laboratory with time to identify irregular antibodies and select suitable units.

Crossmatching Guidelines(contd) Antibody screening may be more reliable and sensitive than crossmatching against donor red cells.

Crossmatching Procedure The usual protocol which involves major and minor crossmatch can be immediate spin ( abbreviated crossmatch) or antiglobulin crossmatch . The antiglobulin crossmatch continues the immediate proceeding to incubation at 37°C,Albumin and AHG).

Emergency Crossmatching Guidelines If blood must be issued in an emergency, the patient’s ABO and Rh group should be determined so that compatible group can be given. In extreme conditions when there is no time to obtain and test a sample, group O Rh- negative packed cell can be used.

Emergency Techniques Using LISS The emergency compatibility technique which can be used employs a shortened incubation period. This is achieved with the addition of Low Ionic Strength Saline(LISS) to speed the antigen –antibody complexing. The procedure involves; washing the donor’s red cells with normal saline Suspend the cells with LISS

Emergency Techniques Using LISS(contd) dilute the patient’s serum and donor’s red cell suspension in ratio 2:1 incubate at 37°C for 15 minutes wash the red cells with normal saline and apply AHG spin low and observe for agglutination both macroscopically or microscopically.