Approaches Requiring Less Than a Complete Crossmatch
Type and Screen
The term type and screen refers
to elimination of the crossmatch in which blood is set aside with only the ABO-Rh
type having been determined and antibody screening having been performed. The type
and screen without crossmatch determines the ABO-Rh of the patient and the presence
of the most commonly found unexpected antibodies. Specifically, the patient's serum
is screened for the presence of unexpected antibiotics by incubating it with selected
reagent RBCs (i.e., screen cells).[39]
These cells
contain all antigens capable of inducing clinically significant RBC antibody reactions.
Complete transfusion testing for compatibility between donor and
recipient blood ensures optimal safety and therapeutic effect of transfused blood.
In some cases, however, the crossmatch is eliminated, and blood can be set aside
in which only the ABO-Rh type and antibody screen are performed (i.e., type and screen).
For those few patients in whom the antibody screen reveals the presence of unexpected
antibody, the antibody is subsequently identified in the blood bank, and units of
blood lacking the corresponding antigen are set aside for surgery. If an emergency
transfusion is required after type and screen alone, an immediate-phase crossmatch
is performed before transfusion to eliminate reactions that may result from human
errors in ABO-Rh typing. Blood given in this manner is more than 99% effective in
preventing incompatible transfusion reactions due to unexpected antibodies.[40]
The type and screen without the complete crossmatch does not protect against reactions
due to antibodies reactive against lower-incidence antigens, those not represented
on the screening cells but present on the donor RBCs. Generally, antibodies that
are not detected in the type and screen are weakly reactive antibodies that do not
result in serious hemolytic transfusion reactions. In a study of 13,950 patients,
Oberman and associates[41]
discovered only eight
"clinically significant" antibodies after complete crossmatch that were not detected
during the antibody screening. The antibodies were all in lower titer and were believed
by Oberman and coworkers to be unlikely to cause serious hemolytic reactions.
Type and screen should not be confused with the term type
and hold. The latter term refers to a sample of blood from a potential
blood recipient received by the blood bank in which the blood type but no crossmatch
has been ordered. This term is misleading because it does not denote how long the
blood should be held, nor does it indicate that an antibody screen has been performed
on the sample. However, in most cases in which a type and hold has been ordered,
an antibody screen is performed on that sample. Because of the confusion that has
arisen with type and screen, the type and hold terminology and method of ordering
blood have been abandoned by most blood banks.
Maximal Surgical Blood Order Schedule
Routine preoperative crossmatching of blood for surgical cases
means that crossmatched blood is unavailable for others for 24 to 48 hours. During
this time, 1 to 2 days is lost, and the chance for outdating increases. A second
aspect relates to the growing realization that, for certain elective surgical procedures,
the number of crossmatched units that are ordered frequently far exceeds the number
actually transfused. To quantify this problem better, the crossmatch-to-transfusion
(C/T) ratio has been used. If the C/T ratio is high, the blood bank is burdened
with keeping a large blood inventory, using excessive personnel time, and having
a high incidence of outdated units. Sarma[42]
recommended
that for surgical procedures in which the average number of units transfused per
case is less than 0.5, determination of the ABO-Rh type and a screen of the patient
serum for unexpected antibodies (type and screen) should be used. This would be
in lieu of a complete type and crossmatch for patients with negative antibody screens.
For those with a positive antibody screen, the blood bank must provide compatible
units that lack the corresponding antigen. Blood banks attempt to maintain C/T ratios
of 2.1 to 2.7.[42]
To increase the rate of use
and lower the C/T ratio, blood banks attempt to decrease the emphasis on crossmatching
of blood through such means as the type and screen and such programs as the maximal
surgical blood order schedule.[43]
This schedule
consists of a list of surgical procedures and the maximum number of units of blood
that the blood bank will crossmatch for each procedure. This schedule is based on
the blood transfusion experience for surgical cases in hospitals in which the schedule
is employed. Each hospital's maximal surgical blood order schedule is developed
by the suppliers and the users of blood in that hospital, such as blood bankers,
anesthesiologists, and surgeons.
Is the Crossmatch Really Needed?
In previously transfused or pregnant patients, only about 1 patient
in 100 may have an irregular antibody other than the anti-A and anti-B antibodies.
However, some of these irregular antibodies are reactive only at temperatures
below 30°C and therefore are insignificant in most transfusions. Others that
are reactive at about 30°C can produce serious reactions if the transfused cells
contain appropriate antigen. In order of probable significance, anti-Rh(D), Kell,
C, E, and Kidd are the most common of clinically significant antibodies. After anti-A
and anti-B, anti-Rh(D) is the most common significant antibody. If the correct ABO
and Rh blood type is given, the possibility of transfusing incompatible blood is
less than 1 chance in 1000. Put in other terms, ABO-Rh typing alone results in a
99.8% chance of a compatible transfusion, the addition of an antibody screen increases
the safety to 99.94%, and a crossmatch increases this to 99.95%.[44]
The blood bank can reduce the chance of incompatibility by performing
an antibody screen. The chance of this screening test's missing an antibody that
is potentially dangerous has been estimated to be no more than 1 in 10,000.
