Avoiding haemloysis of blood samples is germane in every medical laboratory work so as to achieve accurate analysis of test samples and to give a precision guided diagnosis of the ailment or condition of a patient. Procedures and laboratory methodologies on how to avoid haemolysis must be carried out with scientific precision to ensure good results from diagnostic analysis.
Haemolysis can be avoided by:
- Checking that the syringe and needle are dry and that the barrel and plunger of the syringe fit well.
- Not using a needle with too fine a bore.
- Not withdrawing the blood too rapidly or moving the needle once it is in the vein. Frothing of the blood must be avoided.
- Removing the needle from the syringe before dispensing the blood into the specimen container and allowing the blood to run gently down the inside wall of the container.
- Adding the correct amount of blood to anticoagulant. Do not shake the blood but gently mix it with the anticoagulant.
- Using clean dry glass tubes or bottles for blood from which serum is required and by allowing sufficient time for the blood to clot and clot retraction to take place. Red cells are very easily haemolyzed by the rough use of an applicator stick to dislodge a clot.
- Centrifuging blood samples for a minimum period of time. Centrifuging for a minutes at about 1000g is adequate to obtain serum or plasma.
- Not storing whole blood samples in, or next to, the freezing compartment of a refrigerator.
Stability of Anticoagulated Blood
EDTA anticoagulated blood: When EDTA anticoagulated blood cannot be tested within 1-2 hours it must be refrigerated at 4-8 C to prevent cellular changes affecting test results. Manuel or automated blood cell counts, reticulocyte count, and OCV change little in EDTA blood at 4-8 C when stored for up to 24 hours. Haemoglobin concentration is stable for 2-3 days at 4-8 C providing there is no haemolysis.
Important Note: Blood which has been refrigerated must be allowed to warm to room temperature and be well mixed before being tested.
Blood Films: In EDTA anticoagulated blood, morphological blood cell changes occur soon after blood is collected when it is stored at room temperature (18-25C) and within 3 hours when stored at 4-8C it is therefore recommended that blood films be made and methanol-fixed as soon as possible after blood is collected and never made after overnight storage. Some of the blood cell changes which occur in EDTA blood include:
- Neutrophil degeneration with neutrophils becoming more irregular in shape, nuclear lobes separating, and vacuoles appearing in the cytoplasm. There is also loss of granules.
- Segmentation (budding) of the nucleus of lymphocytes and monocytes and vacuoles appearing in the cytoplasm.
- Erythrocytes becoming crenated and spherocytic.
- Platelets disintegrating.
Citrate anticoagulated blood: Even when citrated blood is stored at 4-8C, there is a decrease in the ESR due to change in erythrocyte shape affecting rouleaux. The ESR should be measured within 4 hours of collecting the blood. Coagulation tests should be carried out as soon as possible after blood is collected into citrate anticoagulant.