1) Work-up.
Needs a purple top and large red top tube, ideally. A patient who is
suspected of having a warm autoantibody should first have direct and
indirect antiglobulin testing performed (e.g. direct Coombs' test and
antibody screening). If both are negative, it is unlikely that the
patient has a warm autoantibody. However, if the patient has highly
suspicious findings, consider the following situations that could
lead to a negative DAT with warm autoantibody:
2) Classic serologic findings.
Patients with a warm autoantibody usually have a positive DAT (could
be any strength) with IgG. Complement may also be present.
Approximately 10% of patients with WAIHA have only C3 detectable on
their RBCs (i.e. no IgG). The antibody screen is often positive, but
not always. Most commonly, the serum antibody reacts with equal
strength with all donor cells tested. Eluate will also be positive,
usually with all donor cells tested. Some warm autoantibodies may
simulate the specificity of an alloantibody. You will detect that
this is an autoantibody because their RBCs will phenotype positive
for the antigen the autoantibody is recognizing. Most commonly, warm
autoantibodies are of the Rh specificity, especially anti-e.
3) Special studies.
If transfusion is requested, additional work may need to be done.
Consider autoabsorption --- removal of the autoantibody from the
patient's serum by using his own red blood cells as "sponges" to soak
the autoantibody up. Several cycles of treatment of the RBCs with
ZZAP to remove the antibody, then incubating it with the serum may be
done. Also consider phenotyping the patient's RBCs after chloroquine
treatment. You may wish to consult a supervisor or faculty member if
questions about these procedures come up. These procedures are quite
time-consuming and may not be possible under emergency
circumstances.
4) Transfusion.
Transfusion with RBCs should be avoided whenever possible. However,
if truly needed, do not hesitate to issue blood ("least
incompatible"). The blood will be incompatible, so must be issued on
a "blue card." The clinical team must be aware, however, that the
patient must be closely observed and the transfusion given slowly,
since the risk of hemolysis of all transfused RBCs exists. If the
autoantibody shows specificity, mimicking an alloantibody, PMH
transfusion service routinely ignores the specificity. Blood for
transfusion is selected on the basis of ABO, Rh and alloantibodies
present only. Leukocyte reduced blood products may be given to
prevent a febrile, nonhemolytic transfusion reaction.
Also called cold agglutinins. Do not confuse with cryoglobulins! Cryoglobulins are proteins (not necessarily red cell antibodies) that precipitate in the cold. They may cause occlusion of small vessels with ischemic symptoms. Cold agglutinins on the other hand generally cause hemolysis. Cryoglobulin testing is done in the hematology laboratory. Cold autoantibodies are red cell antibodies that react more strongly at temperatures below 37oC. They may be clinically significant or may only interfere with in vitro testing. Typically they may interfere with ABO grouping (room temperature testing), but not antibody screening (37o testing).
1) Work-up.
If there is a clinical suspicion of a cold agglutinin, do a DAT
first! Remember, the DAT must be performed on a purple top (EDTA)
tube to avoid false positive reactions. The DAT should be positive
for complement if a clinically significant cold agglutinin is
present. If the DAT is negative, it is highly unlikely that the
patient has a clinically significant cold agglutinin. Only in the
case of overwhelming hemolysis, where all coated RBCs are destroyed,
should the DAT be negative. If the DAT is negative, in most cases the
work-up for autoimmune hemolytic anemia can be stopped. The DAT can
be done in 15 to 20 minutes, even on the off hours.
2) Classic serologic findings.
In addition to the DAT positive for complement, an ABO discrepancy
may exist. In addition, any antibody screening performed at room
temperature or 4°C may show reactivity with all panel cells.
3) Special studies.
Need a warm-collected and warm-transported sample of blood (purple
top tube). The specimen must be brought directly to blood bank lab
(not CSR). As soon as it is spun to separate the plasma from the
cells, it can be stored in the refrigerator. But it is of paramount
importance to keep it at body temperature until then. A thermos is
available in the blood bank lab for filling with hot water for
transportation which the clinicians can borrow. Cold agglutinin
titers are performed at 4oC with doubling dilutions in
saline. A titer of at least 32 must exist before it is considered
clinically significant. Most cold agglutinins causing clinical
hemolysis have titers in the hundreds to thousands. Thermal
amplitude studies may be performed on the same specimen to
determine at how high a temperature the antibody maintains its
reactivity. The higher the temperature at which reactivity occurs,
the more likely the autoantibody is to be clinically significant.
Testing is typically done at 25oC and 30oC.
Reactivity of any titer at 25 or 30 degrees is suspicious for
clinical significance. Reactivity showing up more strongly in albumin
enhancement may be an indicator of clinical significance as well.
Testing for anti-i and anti-I reactivity are also routinely performed
as part of this evaluation. This information is largely academic.
NOTE: thermal amplitude studies are generally not performed on
a STAT basis. Typically, the physicians understand that staffing at
night and on weekends does not allow for such labor-intensive studies
to be performed.
Mycoplasma pneumoniae work-up. If cold agglutinin titers are
requested to help make a diagnosis of mycoplasma pneumonia, evaluate
the following:
If there is evidence for hemolytic anemia, we should proceed by doing a DAT. If the DAT is positive for complement, it is appropriate to then do a cold agglutinin titer. If there is no evidence of hemolytic anemia, or a DAT has already been done and is negative for complement, we should not do a cold agglutinin titer. Advise the physicians that the chance of a clinically significant cold agglutinin is minimal in the face of a negative DAT and that doing a cold agglutinin titer is very nonspecific, as many of us have low titer cold agglutinins. Suggest that the clinicians order a specific test for Mycoplasma pneumoniae. In PMH the available test is a complement fixation assay performed in the virology lab.
4) Transfusion.
Patients with cold autoantibodies need to be kept warm! This means a
warm room and lots of blankets. Whether or not transfusion must be
performed using a blood warmer is somewhat controversial. However, it
certainly won't hurt, so most clinicians probably will use a blood
warmer. Compatibility testing is generally not impaired by the
autoantibody, so a blue card is not necessary. Leukocyte reduced
blood products may be given to prevent a febrile, nonhemolytic
transfusion reaction.
Do not confuse with paroxysmal nocturnal hemoglobinuria (PNH). PNH is an acquired, long-lasting red cell defect resulting in increased lysis in the presence of complement. PCH, on the other hand, is caused by an autoantibody which becomes active at temperatures below 37oC. It is considered a biphasic antibody because the antibody binds to RBCs in the cold then releases from the RBCs as the temperature is warmed and the cells hemolyze. The autoantibody specificity is usually to the P blood group antigen.
1) Testing.
Do a DAT first. If it is positive for complement, further testing is
warranted. A warm-collected and warm-transported serum sample is
necessary. Have the clinicians borrow the thermos from the blood bank
lab and fill it with 37oC water. Then a red top tube
(clotted specimen) is drawn and immediately placed in the warm water
and transported directly to the blood bank (not CSR). The specimen
must be centrifuged immediately to separate serum and cells, then can
be stored in the refrigerator until testing is performed.
The test to perform if PCH is suspected is the Donath-Landsteiner
test. If it is positive, then the patient has PCH -- it is as
pathognomonic as any lab test available. If it is negative, the
patient does not have PCH. It may be difficult to get this test
performed at odd hours because of staffing limitations. The specimen
can be collected at any time and stored after separation (see above).
You will have to decide if testing can wait until the next working
day.
2) Classic serologic findings.
The DAT should be positive for complement only. An eluate would not
be helpful and shouldn't be done if the DAT does not show evidence of
IgG. The antibody screen is generally negative.
3) Transfusion.
The antibody of PCH does not generally interfere with serologic
testing. Therefore, compatible blood should be found with little
difficulty, and a blue card is not necessary. Use of a blood warmer
is probably indicated (see discussion for cold agglutinins, above).
Blood lacking the P antigen would be difficult to obtain, so the
specificity of the autoantibody is not honored. Leukocyte reduced
blood products may be given to prevent a febrile, nonhemolytic
transfusion reaction.
Return to Transfusion Medicine Table of
Contents
Return to Call Manual Table of Contents