UCSF: Laboratory Techniques

Question 1

Causes of ABO discrepancies

Answer 1

Chimera: Blood transfusions, Transplanted bone marrows or peripheral blood stem cells, Exchange transfusions, Fetal-maternal bleeding
Technical Errors: Inadequate identification of blood specimens, test tubes, or slides, Cell suspension either too heavy or too light, Clerical errors
, A mix-up in samples
, Missed observation of hemolysis, Failure to add reagents
, Failure to follow manufacturer’s instructions, Un-calibrated centrifuge
, Contaminated reagents
, Warming during centrifugation

Question 2

ABO Discrepancy Groupings

Answer 2

Group I: Reverse typing doesn’t match, caused by weakly reacting or missing antibodies due to decrease antibody production (neonates, elderly, immunocompromised, patients with bone marrow problems, dilution from plasma transfusion, ABO subgroups)
Group II: Forward typing discrepancies from A or B subgroups, leukemia patients, Acquired A and B phenomenon
Group III: Caused by protein or plasma abnormalities and produce rouleux or pseudoagglutination in testing (Elevated globulin levels, high fibrinogen, plasma expanders and Wharton’s jelly)
Group IV: Cold reactive autoantibodies that cause spontaneous agglutination, ABO isoagglutinins, non-ABO alloantibodies

Question 3

What are the causes of false negative Coombs tests?

Answer 3

Specimen not drawn into EDTA tube, complement attaches while sample clots.
Inadequate washing of the cells so there are free antibodies present.
Presence of fibrin
Degenerated/Forgotten reagent
Cell suspension too heavy
Too heavy a cell suspension
Delay in cell washing
Inadequate centrifuging

Question 4

What is the purpose of crossmatch?

Answer 4

To check the compatibility of the patient’s plasma with the donor cells, this is to prevent the patient from having a transfusion reaction when given the transfusion.

Question 5

What causes RBC mix-field results?

Answer 5

Mixed field results are seen when two populations of RBCs are present in a sample. Patients who demonstrate this include:
Recently transfused patients
Chimeras
Fetomaternal hemorrhage

Question 6

Purposes of Adsorbtion and Elution

Answer 6

Adsorption: Providing an antibody with its corresponding antigen under optimal conditions so that the antibody will attach to the antigen, thereby removing the antibody from the serum; often used interchangeably with absorption.

Elution: A process whereby cells that are coated with antibody are treated in such a manner as to disrupt the bonds between the antigen and antibody. The freed antibody is collected in an inert diluent such as saline or 6% albumin. This antibody serum then can be tested to identify its specificity using routine methods. The mechanism to free the antibody may be physical (heating, shaking) or chemical (ether, acid), and the harvested antibody-containing fluid is called an eluate.

Question 7

How do you counteract cold autoantibodies in testing?

Answer 7

Place the samples in a 4C refrigerator and let them incubate for 15-30min before spinning.

Question 8

Emergency Release Guidelines

Answer 8

Emergency release of group O, Rh-negative, un-crossmatched red cells for an actively bleeding patient requiring transfusion before compatibility testing can be completed. These products are not irradiated. Units are leukoreduced; but not necessarily CMV sero-negative.
Process:
• Call Blood Bank STAT
• Blood Bank confirms request for emergency release of uncrossmatched red blood cells
• Provide patient’s name, MRN, location and name of MD approving Emergency Release
• Draw blood bank specimens prior to administering blood and send STAT
• Send staff to Blood Bank STAT with a Blood Product Pick-Up form.
• 4 group O, Rh negative, uncrossmatched RBC units are provided in a cooler within 5 min
• If additional units are required, call Blood Bank
• Return unused blood products to the Blood Bank ASAP

Question 9

How do you define positive antigen-antibody reaction?

Answer 9

Formation of a cell button that does not dissolve with agitation, grading based on the degree of break-up of the button when the tube is agitated.
1+/W+: Very small agglutinates on a turbid background
2+: Small agglutinates on a turbid or clear background
3+: Large or Medium-sized agglutinates on a clear background
4+: Large intact agglutinate with clear background

Question 10

What type of AHG is needed to detect the clinically significant antibody Jk^a?

Answer 10

Polyclonal as the anti-C3 is needed for detection

Question 11

What are Coombs cells made of?

Answer 11

RBC’s coated with IgG antibodies

Question 12

PEG increases the strength of agglutination reactions by:

Answer 12

Increasing water removal from the surface of the RBC

Question 13

What is the frequency of the Duffy Antigen in the Black population?

Answer 13

70% are Fy(a-b-), this same phenotype is rare in the white population

Question 14

What type of blood can an AB person receive?

Answer 14

They may receive RBCs from any blood group, but not the plasma.

Question 15

How do you calculate how many units will need to be crossmatched to find a compatible match?

Answer 15

Take the incidence of antigen negative blood for every antigen that needs to be negative and multiply them together.
take this number and divide by the number of units needed to find how many units should be screened.

Question 16

In an emergency situation where an Emergency Release has been approved, what RBCs should be given immediately?

Answer 16

Uncrossmatched O units until the patient’s type can be confirmed. +/- will be given based on gender; pos can go to a neg male patient, neg should go to female patients of reproductive age.