Donor Testing Flashcards
What was the first required infectious disease test?
Syphilis testing began in the 1940’s and was required in 1950’s
What units need to be tested for Trypanosoma cruzi (Chagas disease)?
Initial testing
What units need to be tested for Babesia microti (babesiosis)?
Many units in high-riskregions of the US
What happens if a test is reactive?
All initially reactive samples are retested in the same assay system in duplicate. If one or both of the duplicate tests are also reactive the sample is classified as repeat reactive and is, by definition, positive. A positive screening test results in the destruction of the unit. If both repeat test results are negative, the initially reactive result is equivalent to a negative result and the unit is released from quarantine.
Are donors tested for Hep A?
Hepatitis A (HAV) is not currently tested for in the US
HAV rarely is transmitted by blood transfusion.
Not tested for due to
-No licensed test
-Rarity of transmission in adults
-HAV has short infection period (7-14 days)
-Low incidence of HAV in the US (20/100, 000)
-Absence of carrier state
-Prevalence of immunity from vaccination in many recipients
What is the principle of direct binding in EIA?
Specific antigen or antibody is coated onto a bead or microwell by manufacturer.
Corresponding antibody or antigen in a sample, if present, binds to solid phase, forming an immune complex.
Enzyme-labeled conjugate (an anti-IgG) attaches to antigen/antibody complex, if present
Substrate is oxidized by enzyme-labeled conjugate, resulting in colored end-product, proportional to the amount of antigen or antibody present in the sample
What is the principle of competitive binding EIA?
Specimen containing the antibody to be determined is mixed with enzyme-labeled antibody.
The two compete for limited binding sites on an antigen coated solid phase
Addition of substrate causes color change which is inversely proportional to amount of antibody present
How is WNV tested?
Can be in MP-NAT
May be IDT-NAT during outbreaks
How is Zika tested?
IDT-NAT since 2016
What is the principle of NAT?
Reverse transcription of the target RNA to generate complementary DNA (cDNA).
Polymerase chain reaction (PCR) of specific complementary primers.
Hybridization of the amplified products to oligonucleotide probes specific to the target.
Detection of the probe-bound amplified products by colorimetric determination.
How effective is culture based bacterial detection?
A study evaluating the BACTEC 9240 blood culture system for detection of nine species of bacteria commonly associated with platelet contamination noted a detection sensitivity of <10 colony-forming units (CFUs) per mL for all pathogens tested except for Streptococcus mitis (detection limit of 61 CFUs per mL). The time to detection ranged from 6.5 to 17.6 hours.
What are the testing requirements for Babesia (B.microti)?
Two FDA-approved investigational blood donor screening approaches for B. microti;
1) Detects antibody using an enzyme-based immunoassay
2) Combined approach detects antibody using an automated immunofluorescence assay along with a PCR-based babesia nucleic acid assay.
Although testing for babesia is not mandatory, many units of blood collected in high-risk regions of the US
What happens if the ABO/Rh can’t be determined on a unit?
If the ABO/Rh cannot be determined, then the product cannot be labeled
What happens if a donor unit ABO is mislabeled?
Reportable to the FDA
What is the requirement for Rh testing on donor units?
The Rh type shall be determined for each collection with anti-D reagent. If the initial testing with anti-D is negative, the blood shall be tested using a method designated to detect weak D. When either testing is positive, the label shall read “Rh Positive.” When the testing for both are negative, the label shall read “Rh Negative.
What is the requirement for ABS testing?
Serum or plasma from donors with a history of transfusion or pregnancy shall be tested for unexpected antibodies to red cell antigens.
Methods for testing shall be those that demonstrate clinically significant red cell antibodies.
How are units with ABO subgroups labeled?
They must be labeled with the ABO and the subtype labeled to notify the transfusion service receiving the product
How are units with antibodies handled?
May be used for patients if the patient lacks the corresponding antigen. Example, donation has anti-K, then unit is K- and the patient is K-. Some transfusion services can use these units, others choose not to accept these antibody positive units.
“Contains ( name of antibody)” must be on the product
What are the most common types of weak D?
In Caucasians, its types 1, 2, and 3 that make up 90% of weak D
They will not make anti-D
What is Ce in trans?
If Ce (r’) in trans to RHD (ie, Ror’), then the D antigen will be suppressed. This can lead to a donor/patient to type as Rh negative (rr’, r’r’ or r’’r’) This occurs when C is present in trans to a weak D type. (r’ in trans to weak D Type 2) A detection strategy for this weak D type can be screened for by typing all D- donors for the C antigen
What reagents are used to determine Rh?
The two anti-D reagents are chosen to be Highly sensitive Able to detect Weak and Partial D - Weaker expression of D - Especially DVI cells
What is the window period for HBV?
3-4 weeks or 26.5 to 18.5 days
What is window period for HCV?
7.4 days
What is the Window period for HIV?
9.1 days
What is multiplex PCR
6-16 mini pools or donors are tested for HIV, HBV, and HCV using NAT
When is a look back required by law?
Only for HIV or HCV
What is the most common bacterial found in RBC units?
Yersina entrocolitica and pseudomonas sp
Also see normal skin flora such as Staph, P. acnes, and bacillus
What causes Chagas?
Parasite Trypanosoma cruzi transmite by triatomine (Reduvid bug after biting and depositing feces in wound. Also transmited by blood transfusion and organ transplantation
What test is used to detect T. cruzi in donors?
EIA to detect antibodies is done on first donation only. Repeat positive donors are deferred indefinitely.
What is the confirmatory test for T. cruzi?
NO FDA licensed test but Enzyme strip assay or Radioimmuno-precipitation (RIPA) can be performed
How is babesiosis transmitted?
Parasite is spread through bite of infected deer tick or blood transfusion
How long can B. microti survive in stored blood?
21-35 days
Which areas are endemic for B. microti?
Northeast, mid-alantic, and upper Midwest
