Weak D

anti-C3d and anti-IgI

polyspecific AHG reagent

direct antiglobulin test (DAT)

positive DAT indicates coating of RBCs with an antibody

partial D

some D-positive RBCs can be missing parts of the D antigen complex

IAT two-stage testing

stage 1: antibodies combine with antigens (requires incubation) stage 2: washing the RBC, followed by addition of AHG reagent

weak D position effect can be found when

the C allele is inherited trans to D

preventing HDFN by using

RhIg (passive IgG anti-D) - protects D negative mother from becoming immunized by exposure to D positive fetal cells

kernicterus

accumulation of lipid-rich tissue

if IAT is negative

add IgG-coated RBCs, agglutination is expected

positive IAT test

agglutination is observed after adding AHG indicated presence of D antigen on RBC

AHG

anti human globulin

(AHG) Anti-Human globulin are

antibodies against human antibodies

the D antigen

is second only to ABO antigens in important in transfusions

antigens and the placenta

- IgM cannot cross the placenta - IgG can cross the placenta

false negative IAT

- failure to add AHG - improper washing - under-centrifugation - loss of reagent reactivity (check cells) - under reading - weak red cell suspension

indirect antiglobulin test (IAT)

- used to detect in vitro sensitization of RBCs by IgG antibodies and/or complement - IgG like to react at body temperature so test is inducbated

false positive IAT

-positive DAT - dirty glassware - over-centrifugation - over reading

hemolytic disease of fetus & newborn (HDFN) erythroblastosis fetalis

-results from excessive destruction of fetal red cells by maternal antibodies - production of antibodies in the mother that have been stimulated by foreign (fetal) antigens

AHG is used to detect

IgG coating RBCs in humans

D antigen inheritance

chromosome 1

IgG-coated RBC (Coombs check cells)

control for negative IAT tests, require by the AABB

detection of weak D antigen is done with an

indirect antiglobulin test (IAT) - cannot be detected on an individual with positive DAT

negative IAT test

no agglutination observed after adding AHG, agglutination observed with IgG-coated RBC

immune-mediated antibodies (usually IgG)

- red-cell mediated (pregnancy, transfusion)

HDFN patho and clinical presentation

- anemia and jaundice (can be fatal, hydrops fetalis) - excessive bilirubin levels in neonate (can cause mental retardation, kernicterus)

administration of RhIg

- at 28 weeks gestation - after delivery of a D positive infant (within 72 hours) - after aminocentesis, miscarriage, or ectopic pregnancy (within 72 hours)

how AHG is made

- commercially prepared reagents - inject animal with human antibodies (globulins) - animal sees human antibody as foriegn and mounts an immune response - animal produces AHG - AHG is extracted from animal and purified

different forms of weak D antigen

- inherited weak D gene - position effect: C trans to D - partial D

testing donors for weak D

- the AABB requires testing for weak D on all donors that do not directly agglutinate with anti-D reagents - weak D positive units are labeled as D positive and should be transfused only to D-positive recipients - testing for weak D in recipients is only required in pregnant women - if D antigen is not detected, Rh (d) negative blood is provided