18 Preparation of Red Cell Suspensions

Principle

The ratio of serum to red cells may dramatically affect the sensitivity of agglutination tests. Consistent preparation of 2-5% red cell suspensions is critical to any agglutination test. Commercially prepared 2-5% red cell suspensions serve as a good guide for comparison (by color) in the preparation of cell suspensions.

Related Policies

This procedure applies to all testing that requires red cell suspension preparation.

Specimen

Fresh red cells separated from the serum/plasma ASAP after receiving.

Procedure

Unwashed Cell Suspension-most often used by labs: “time saver”

1. Label 12X75 tube with patient name& MRN or donor unit number and “cell suspension”.
2. Fill the tube ½ full with isotonic saline.
3. Prepare cell suspension by using a transfer pipette to place several drops of red cells from the bottom of the specimen tube or from a cut donor unit segment into the labeled tube and mix with the pipette.
4. Perform visual comparison to that of a reagent red cell suspension by looking at the suspension in the pipette and comparing to the reagent red cell dropper.
5. If the color is too dark, add additional isotonic saline to the tube until the suspension color is right.
6. If the color is too light, add additional drops of cells to the tube until the suspension color is right.
7. Proceed to use the cell suspension for testing.

Washed Cell Suspension: Initial method for student labs

1. Label 12X75 tubes with patient name and MRN or donor unit number and “cell suspension”.
2. Fill the tube ¾ full with isotonic saline.
3. Using a transfer pipette place some red cells from the bottom of the specimen tube or from a cut donor unit segment into the labeled tube and mix with the pipette.
4. Centrifuge the tube for at least 1 minute on high speed. Decant the supernatant fluid with a transfer pipette in the “dirty” sink. This is considered “1 wash”.
5. To the washed cells, add enough saline to produce a red color comparable to that of the reagent red cell suspension (2-5%). Perform a visual comparison between the pipette and the reagent red cell dropper.
6. If the color is too dark, add additional isotonic saline to the tube until the suspension color is right.
7. If the color is too light, repeat steps 3 through 6.
8. Proceed to use the cell suspension for testing.
9. Further washing may be required if testing issues related to coated RCs exist. If so repeat steps 4 and 5 two to three times.

Notes

1. Many Transfusion Medicine labs use “unwashed” cell suspensions as a time saver. Keep in mind that interference due to unwashed cells may occur. Technologists may have to make a new suspension with washed cells if there are any discrepancies.
2. Hemolysis of the red blood cells from improper washing may result in false results.
3. A cell suspension that is too heavy or too light may produce false-positive or false-negative results (prozone or postzone).
4. For best results use red cell suspensions on the day of the preparation only.