58 Cord Specimens
Principle
A sample of cord blood is obtained from the umbilical vein at delivery. Tests can be performed on the sample to help with the assessment of HDN.
Specimen
The sample is obtained by venipuncture using a syringe or vacuum tube phlebotomy. If the cord is “milked” to obtain a specimen Wharton’s jelly may contaminate the sample. Wharton’s jelly may cause rouleaux and can be removed by washing the cord cells several times in saline (sometimes this saline is warmed to better rid the sample of this contaminant).
Reagents
- ABO antisera
- anti-D and Rh control antisera
- AHG (anti-IgG only)
- CCs
- Eluate reagents may be needed to determine the antibody on the infants red cells
Procedure
- ABO testing (refer to SOP for ABO grouping)
- Rh grouping (refer to SOP for Rh grouping)
- DAT using anti-IgG only. (refer to SOP for DAT)
- Eluates may be performed. (refer to elution SOP)
Interpretation
- No reverse grouping is performed in the ABO procedure of newborns because ABO antibodies in the infant’s sample are usually of maternal origin (IgG).
- Infants with a positive DAT may give a false positive with high protein anti-D or if the infant has a strongly positive DAT a false negative Rh grouping result may be obtained due to the fact that all of the Rh antigen sites are blocked by maternal anti-D and are prevented from reacting with the reagent anti-D.
- If the infant has ABO HDN, eluates from the cells usually give positive reactions with adult A or B cells by the IAT.
- If the infant has Rh HDN, the eluate should contain the Rh antibody found in the mother’s prenatal specimens.
- If the mother has two antibodies, eluates may be useful to determine which antibody is on the infant’s cells and therefore which one is causing the hemolytic process.
Notes
- Infants who suffer from severe HDN may require exchange transfusion. This process is performed in such a way to avoid overload of the infants’ circulatory system. A gradual replacement of the infants’ blood is performed by withdrawing and transfusing small amounts into the infant. The goal is to increase the hemoglobin, remove high levels of unconjugated bilirubin in the plasma and decrease the potential for the bilirubin to continue to rise by removing some of the maternal antibody and sensitized cells. Donor blood that is used for the exchange shall (by CSA Z902 standards) be ABO and Rh compatible with the neonate and negative for the antigen(s) corresponding to any clinically significant maternal antibody (ies). Generally, the blood will be CMV negative, irradiated, fresh (generally less than 7 days old), and negative for hemoglobin S.
- Infants suffering from mild HDN may be treated with phototherapy (placed under ultraviolet lights). This converts unconjugated bilirubin to a water-soluble form, which can be excreted.