Autoimmune disorders

Question 1

What is the positive predictive value of a positive DAT? How does the presence of hemolysis affect this?

Answer 1

If hemolysis labs are positive, PPV is 83%. If negative, 1.4%.

Question 2

What conditions can cause a positive DAT?

Answer 2

Hemolytic transfusion reactions, HDFN, AIHA, DIHA…

Question 3

What can cause nonspecific DAT positivity?

Answer 3

Passive antibodies (IVIG), protein adsorption, complement adsorption and activation.

Question 4

How can DAT due to mistransfusion be distinguished from other causes?

Answer 4

Look for mixed-field reactivity

Question 5

What methods can be used to elute antibodies from a positive DAT?

Answer 5

Acid elution (preferred)
Heat/freeze-thaw (for ABO only).

Question 6

How should DAT eluates compare to plasma reactivity in WAIHA?

Answer 6

Antibodies usually end up on the DAT first; if the plasma screen is panreactive, expect the DAT and eluates to be strongly reactive.

Question 7

How can warm autoantibodies be enhanced or subtracted?

Answer 7

Enhance: Use PEG(?), enzymes, gel
Subtract: Use LISS

Question 8

When warm autoantibodies have antigen specificities, what are they generally targeted towards

Answer 8

Usually Rh antigens&raquo_space; LW, Kell, Kidd, Duffy, Diego

Question 9

What conditions cause cold agglutinin disease?

Answer 9

Mycoplasma infection (acute), lymphomas (chronic)

Question 10

What options exist to subtract cold agglutinins on lab testing?

Answer 10

Pre-warm, use 0.01M DTT, or use RESt… carefully

Question 11

What antibodies will RESt remove?

Answer 11

Cold agglutinins, but also D, E, Vel

Question 12

What antibodies will HPC remove?

Answer 12

HLA, all carbohydrate antigens (ABO, I, P, Le)

Question 13

What is the specificity of cold agglutinins?

Answer 13

Usually auto-anti-I. Rarely anti-i, anti-i+, or anti-Pr

Question 14

What is mixed AIHA?

Answer 14

WAIHA but with cold agglutinins acting at 30C. Could be due to WAIHA+CAD or a high thermal amplitude cold agglutinin. Note IgG and C3 should both be reactive on DAT.

Question 15

Paroxysmal cold hemoglobinuria

Answer 15

Transient response to infxn (formerly syphilis) where a cold-reactive and complement binding IgG (anti-P) causes hemolysis. Presents with DAT+ with anti-C3 or anti-IgG.

Question 16

How can PCH be treated? In who is it worse?

Answer 16

Worse in children (higher thermal amplitude). Could transfuse P-negative blood, if you can find it.

Question 17

What are the three mechanisms of drug induced hemolytic anemia?

Answer 17

Antibody may be targeted against drug, combined neoepitope, or just red cell membranes.

Question 18

What drugs tend to cause DIHA in a drug-independent fashion?

Answer 18

Fludarabine, methyldopa

Question 19

What drugs tend to cause DIHA in a drug-dependent fashion?

Answer 19

Beta-lactams, quinine, platinum drugs…

Question 20

What is the behavior of a drug-dependent DIHA?

Answer 20

Once immunized, only a small amount of drug will precipitate hemolysis, which can be brisk and intravascular. Testing requires presence of drug.

Question 21

What antibodies are hardest to elute from DAT+ cells?

Answer 21

IgMs

Question 22

What options remain to identify a suspected AIHA when DAT is negative?

Answer 22

Consider IgM-mediated AIHA. Can try flow, ADCC assays, chemiluminescence or monocyte monolayer assays.

Question 23

Are primary or secondary AIHAs more common? Warm, cold, or mixed?

Answer 23

Secondary is more common! Warm > Cold > Mixed & Drug

Question 24

What is the mechanism of red cell clearance in warm AIHA?

Answer 24

IgG1/3 coating, limited complement activation in the form of C3b deposition which accelerates removal by macrophages.

Question 25

What are secondary causes of warm AIHA?

Answer 25

B-cell neoplasms (note: the neoplastic lineage is NOT which produces the antibodies)
Ovarian dermoids
Kaposi’s sarcoma? HIV? Babesia microti?

Question 26

How sensitive must a DAT be to detect AIHA?

Answer 26

Should be able to detect at 100-500 molecules per RBC of IgG and 400-1100 molecules of C3D.

Question 27

When are cold antibodies clinically significant?

Answer 27

Generally only when the titer is >64 (but usually actually in 1000s) and acting ad broad thermal amplitude.

Question 28

What are secondary causes of cold AIHA?

Answer 28

B-cell neoplasms (including LPL/WM)
Mycoplasma infection
Epstein-Barr virus infection

Question 29

How does AIHA due to IgA usually present?

Answer 29

Cold-like pattern with acrocyanosis but without significant hemolysis.

Question 30

DIHA: Hapten model

Answer 30

Drug binds strongly to membrane, reaction only occurs in presence of drug. IgG, not C3.

Question 31

DIHA: Complex model

Answer 31

Drug binds loosely to antibody in circulation. IgM > IgG.

Question 32

DIHA: Drug-independent models

Answer 32

Drug induces antibody production in non-immunologic fashion, or alters membrane to cause non-immunologic protein adsorption.