Type and Screen and Crossmatch

Pretransfusion testing confirms the recipient's ABO and RhD group, detects clinically significant red cell antibodies and selects compatible red cells. Type and screen is the group plus antibody screen, and crossmatch is the additional check that selected red cells are compatible with the recipient's plasma. The entire process depends on a correctly identified sample from the right patient. Wrong blood in tube errors are a leading cause of ABO incompatible transfusion.

Safety preparation.

• Take the sample from the patient in front of you, labelled at the bedside.

• Use at least two independent identifiers from the wristband (full name and unique hospital number, plus date of birth where used).

• Never pre-label tubes or label away from the patient.

• Record the date, time and signature of the person taking the sample.

• Do not take samples from an arm with an infusion running.

Special groups.

• Neonates: testing is done on the infant's sample, with a maternal sample to look for antibodies; once the first infant sample shows no clinically significant antibodies, repeat crossmatching is often not needed for the first 4 months of life.

• Pregnancy and recently transfused patients: samples are valid only for a short window (usually 72 hours) because new antibodies can appear.

• Patients with sickle cell disease and those transfused often benefit from extended phenotyping.

Sample. Usually 6 mL in EDTA for an adult, and a small volume in a paediatric tube for infants, as the laboratory requires.

Request form. Patient identifiers, diagnosis, indication, products requested, special requirements, history of transfusion or pregnancy, known antibodies, urgency and the requesting clinician.

Laboratory steps.

1. ABO forward and reverse grouping and RhD typing.

2. Antibody screen with 2 to 3 reagent red cell panels at 37 degrees Celsius with indirect antiglobulin technique.

3. Comparison with historical results.

4. Crossmatch: immediate spin (to confirm ABO compatibility), full antiglobulin crossmatch, or electronic crossmatch in laboratories with validated systems, a negative antibody screen and two concordant group determinations.

Sample validity. Usually 72 hours when the patient has been transfused or pregnant in the previous 3 months, and longer for patients without such exposure where the laboratory permits.

Timing. Group and screen takes roughly 30 to 45 minutes. Antiglobulin crossmatch adds roughly 45 minutes. Antibody identification can take hours or longer and may need referral.

Type and screen versus crossmatch.

• Type and screen only: for procedures with low probability of transfusion, using a maximum surgical blood order schedule. Compatible blood is issued if needed after electronic or immediate spin crossmatch.

• Full crossmatch: when transfusion is likely, antibodies are present or the patient has a history of reactions.

Steps for the clinician.

1. Identify the patient at the bedside.

2. Take the sample and label it at the bedside.

3. Complete the request form clearly, with indication and urgency.

4. Deliver the sample to the laboratory promptly.

5. Confirm that results are available before the planned transfusion time.

6. If the antibody screen is positive, speak to the laboratory about the time needed.

If the screen is positive. The laboratory identifies the antibody, tests for antigen negative units, and performs a full crossmatch. Clinically significant antibodies react at 37 degrees Celsius or by the antiglobulin test, for example anti-D, anti-c, anti-E, anti-K, anti-Fya and anti-Jka. Cold reactive antibodies such as anti-Lewis, anti-P1, and anti-M seldom matter if not reactive at 37 degrees Celsius.

If the sample is rejected. A mislabelled or unlabelled sample is rejected, and a new sample must be taken. Never correct a label.

Complications of poor practice. ABO incompatible transfusion, delayed haemolysis from missed antibodies, delays in emergency care, and wastage of units.

Documentation. Time of sampling, the person who took the sample, tests ordered, results, units issued and the remaining crossmatch validity.

Quality assurance. Second sample confirmation for first time group determinations is used in many hospitals. Rejection of inadequate samples and audits of sampling errors improve safety. Electronic crossmatch needs validated software.

Referral and escalation. Blood bank medical staff and the haematologist for positive antibody screens, discrepant results or delay in compatible blood.