Chapter 14 Testing of Donor Blood Flashcards
What two categories can donor tests be divided into?
- Immunohematologic testing (Type & Screen).
- Infectious disease screening.
What immunohematologic ABO, D and K tests are done on donors?
ABO, D and K testing
1. Forward and reverse testing is performed
2. Weak D testing is performed on all negative donors
3. K antigen testing is now performed on donors - if it comes back negative twice, it is indicated K negative on units.
What other type besides ABO, D and K phenotyping is done on a subset of donors?
Phenotyping for C,c,E,e,Jka, Jkb, Fya, Fyb, S,s is routinely performed on a subset of donor samples. This helps find units quickly for those that have clinically significant antibodies.
What type of genotyping is done on some donor units?
Red blood cell antigen genotyping is also done on some donor units. This allows for identification of certain rare phenotypes
What are different ways the antibody screen can be done? How do the results affect the usage?
Antibody screen
1. Screening cells can be separated or pooled
2. If significant antibodies are present, plasma and platelets cannot be used
RBCs can be used, but the antibody interpretation should be on the label
Describe in general the testing program for transmissible disease in donor blood by CBS?
- There are lab tests performed on every donation to detect specific agents:
- These are for diseases that are easy to test for and known to be transmitted through blood
- This helps to keep the Canadian Blood System safe
- These are not run at all CBS locations but sent to large centers in Alberta and Ontario.
Are all diseases tested for in the donor’s blood?
Some diseases cannot be easily tested and are only ruled out by the screening questionnaire
What is HIV-1/2?
Human Immune Deficiency Virus (HIV) - 1/2 cause Acquired Immunodeficiency Syndrome (AIDS)
Infects CD4+ T lymphocytes (helper T cells)
What is the testing required for HIV-1/2?
Screening tests
1. Antibody to HIV - 1/2 develops 22 to 25 days after infection (chemiluminscent assay)
2. HIV NAT – run on pooled donor plasma (6 patients put together)
Confirmatory/Supplemental Tests
1. Anti-HIV-2- EIA
What is HBsAg?
Hepatitis B surface antigen (HBsAg)
HBsAg is a protein on the viral surface; it indicates that the individual is infectious
When does the antibody to HBsAg appear?
Antibody to Hepatitis B core antibody (anti-HBc)
–>Antibody appears after HBsAG but before symptoms
When is Anti-HCV detectable?
Antibody to HCV
–>Anti-HCV antibody is detectable 10 weeks after infection
NAT (Nucleic Acid Testing) to detect DNA of HBV and RNA of HCV (pooled samples)
See slide 10 for table of testing for various Hepatitis viruses.
What is the requirement for testing for Human T-cell Lymphotropic Virus-I/II?
- It is a requirement that all donor blood be tested for antibody to HTLV types I and II
- Screen is done by chemiluminescent assay. Confirmation by HTLV Western blot
Note:
HTLV-I is associated with adult T-cell leukemia
HTLV-II is associated with large granular lymphocyte leukemia
What is the name of the bacterium that causes syphilis?
Syphilis is caused by Treponema pallidum
Spirochete bacterium
What tests (3) are there that can detect a the presence of the bug that causes a syphilis infection? Which one is the screening test?
- Rapid Plasma Reagin Test
Non-specific for T. pallidum, detects reagin which is released during Syphilis infection - Treponemal Tests
a) Microhemagglutination - Sensitized sheep erythrocytes coated with T. pallidum react with patient IgM or IgG antibodies
b) Fluorescent treponemal antibody adsorption
What causes West Nile Virus and what are the symptoms?
- Mosquito-borne flavivirus
- Symptoms range from mild fever to encephalitis, coma, and death
What manner of testing is performed for West Nile Virus?
Pools are screened for West Nile Virus using NAT during peak seasons or individuals in off season that have travelled to certain destinations
What is the confirmatory test for donors suspected with West Nile Virus?
Confirmed with ELISA techniques
What causes Chagas disease and who is tested for it?
Chagas disease
1. Caused by Trypanosoma cruzi; transmitted by reduviid bug
2. Selective testing on at-risk donors (determined by questions)
What is a mononucleosis-like virus that is tested on a select number of random donors?
Cytomegalovirus
1. Mononucleosis-like virus that is found in white blood cells
2. Done on a select number of random donors
CMV-negative blood is given to infants or anyone who is immunocompromised
Who is it important to give CMV-negative blood to?
CMV-negative blood is given to infants or anyone who is immunocompromised
What blood components are tested for bacterial contamination?
Apheresis platelets and pooled platelet concentrates must be tested
What does ELISA stand for and what does it detect via the indirect ELISA and sandwich ELISA?
Enzyme-Linked Immunosorbent Assay (ELISA) detects antigens or antibodies using a solid object (e.g., plastic bead) coated with antigen or antibody
a) Indirect ELISA - detects antibodies
b) Sandwich ELISA - Detects antigen
See slide 16 for diagram.
What is chemiluminescence testing?
Chemiluminescence is the emission of light from a chemical reaction
Chemiliminescent labels are attached to an antigen or antibody where the highest light intensity emitted is measured
What are the advantages of chemiluminescence testing in the TS lab?
Advantages
1. Stable
2. Less reagent is needed
3. Relatively nontoxic
4. Quick reagents
5. Very sensitive
6. Fast turnaround time
What disease is the Western Blot Test used to confirm the presence of in the donor’s blood?
Confirmatory test for antibody to HIV types 1 and 2 and HTLV types I and II
How is the Western Blot Test results determined for HIV 1 and 2 and HTLV types I and II?
- Antibodies in serum are tested for a reaction with individual protein bands (antigen) on strips (done by electrophoresis)
- Patterns are compared with a strip containing all HIV proteins
- Two of the following bands must be positive: p24, p41, or gp120/160.
What is the advantage of doing nucleic acid testing (NAT) on donor blood donations?
- NAT amplifies nucleic acids of infectious agents and identifies viral RNA
- NAT can detect very low numbers of viral copies in plasma before antibodies appear
What viruses are routinely tested using nucleic acid testing (NAT)?
RNA viruses routinely tested using NAT
- HIV
- HCV
- West Nile virus (WNV)
Samples are done in pools of six
What is sensitivity versus specificity?
Sensitivity is ability of assay to identify samples from infected individuals as positive.
Specificity is ability of assay to identify samples from non-infected individuals as negative.
What is the one negative that many screening tests are really sensitive?
Often means there will be false positives.
What is the equation for sensitivity?
Sensitivity = % of # of pos. people/total # of infected individuals tested.
OR
TP/(TP+FN)
where
TP = true positives
FN = false negatives
What is the equation for specificity?
Specificity = % of # of Neg. people/Total # of healthy individuals tested
OR
TN/(TN+FP)
where
TN = true negatives
FP = false positives
What happens if a donor tests positive for a disease by CBS?
Blood products are removed from CBS supplies and a letter is sent to the individual
What if it was determined the person is a false positive by CBS?
Repeat testing is suggested through family physician
What must a donor do if they have had a tested false positive for a disease but would like to try to donate again?
Must go through a donor re-entry program for false reactive screening results following a six month waiting period.
What are pathogen inactivation systems?
They involve chemical or photochemical principles that target and damage DNA and RNA, which would significantly limit replication and growth of bacteria, viruses, and protozoa.
More research is going into pathogen inactivation technologies to make the blood products even safer.
What new treatment for plasma is Canada trying?
Plasma is currently being treated by solvent-detergent or methylene blue followed by UV A lights in several European countries.
Canada is trying solvent-detergent with some restrictions in areas.
What pathogen inactivation method has been approved in Canada for apheresis platelets?
Amotosalen S59 plus UVA illumination is being used in many countries as a pathogen inactivation method for both plasma and platelets. It was approved in Canada, in 2018 for apheresis platelets
