Laboratory
Findings
Autoimmune
Hemolytic Anemia
Autoimmune hemolytic
anemia (AIHA) is identified by autoantibodies that react with RBCs.
These antibodies are detected by the direct antiglobulin (Coombs')
test. Antiglobulin serum is added to washed RBCs from the patient;
agglutination indicates the presence of immunoglobulin or
complement components bound to the RBCs. Alternatively, mixing the
patient's plasma with normal RBCs detects such antibodies (free)
in the plasma (the indirect antiglobulin [Coombs'] test). In
general, the intensity of the direct antiglobulin test correlates
with the number of molecules of IgG or C3 bound to the RBC and,
although not a perfect relationship, with the rate of hemolysis. A
positive indirect antiglobulin test (eg, presence of free anti-RBC
antibodies) in the absence of a positive direct test does not
indicate immune hemolysis; generally it defines an alloantibody
caused by pregnancy, prior transfusions, or lectin
cross-reactivity. Even identification of a warm antibody does not
define hemolysis because 1/10,000 normal blood donors have
positive tests.
Warm
antibody hemolytic anemia is the most common form of AIHA;
it is more frequent in women than in men. Symptoms at presentation
are those of anemia because commonly the onset is abrupt. Slight
splenomegaly is usual. The anemia is usually severe and can be
fatal; the MCHC is high, consistent with the increased spherocytes
and polychromatophilia seen on the smear. The hallmark of AIHA is
a warm-reacting, positive direct antiglobulin test; thus, IgG or
C3 is found on the RBC surface at 37° C (98.6° F). These
antibodies may arise spontaneously, in association with certain
diseases (SLE, lymphoma, chronic lymphatic leukemia), or after
stimulation by a drug (eg, 
-methyldopa,
levodopa). They may also occur as part of a transient haptene
mechanism with drugs such as high-dose penicillin or
cephalosporins, in which the antibody is directed against the
antibiotic-RBC-membrane complex; stopping the drug results in
disappearance of the accelerated destruction.
Three patterns of
direct antiglobulin reaction exist: (1) The direct antiglobulin is
positive with anti-IgG and negative with anti-C3. There is no C3
fixation. This pattern occurs in idiopathic AIHA and in -methyldopa-
and penicillin-induced cases. (2) The direct antiglobulin is
positive with anti-IgG and anti-C3. C3 and antibody are fixed.
This finding occurs in cases with SLE and idiopathic AIHA. It does
not occur in drug-associated cases. (3) The direct antiglobulin is
positive with anti-C3 but negative with anti-IgG. This occurs in
idiopathic AIHA when the IgG antibody is of low affinity, in some
drug-associated cases, and in the cryopathic forms (cold
agglutinin disease, paroxysmal cold hemoglobinuria).
In warm
antibody-mediated AIHA, hemolysis occurs primarily in the spleen;
hemoglobinuria and hemosiderinuria are very rare. Although the
antibodies may have some specificity by virtue of their being
directed against an Rh antigen, almost all are panagglutinins,
making cross-matching difficult. In some typical clinical cases
the direct antiglobulin is negative because the number of
molecules per surface area of the RBC is too small or because the
immunoglobulin on the surface is IgA or IgM.
Therapy in
drug-induced hemolytic anemias includes drug withdrawal, which
decreases the rate of hemolysis. With -methyldopa
and related drugs, hemolysis usually ceases within 3 wk; however,
a positive Coombs' test may persist for > 1 yr. Corticosteroids
occasionally are used in very severe drug-induced hemolysis. With
penicillin and analogous drugs, hemolysis ceases when the drug is
cleared from the plasma.
Corticosteroids are
the treatment of choice in idiopathic AIHA; most patients have an
excellent response, which in about 1/3 will be sustained after
corticosteroid cessation. In patients who relapse after
corticosteroid cessation or who fail corticosteroids, splenectomy
is performed (preferably 2 wk after immunization with pneumococcal
and Haemophilus influenzae vaccines). About 1/3 to 1/2 of
patients have a sustained response after splenectomy. In cases of
fulminant hemolysis, plasma exchange has been effective. For
lesser but uncontrolled hemolysis, immunoglobulin infusions have
provided temporary control. Long-term management with
immunosuppressants (including cyclosporine) has been effective
after failure with corticosteroids and splenectomy.
The presence of
panagglutinating antibodies makes valid cross-matching of donor
blood difficult. In addition, transfusions often result in
superimposition of an alloantibody on the autoantibody, thereby
accelerating the hemolysis. Transfusions should be avoided. When
necessary for cardiopulmonary stability, they should be given only
in small aliquots (100 to 200 mL over 1 to 2 h, watching for
hemolysis).
Cold
antibody disease (cold-agglutinin disease) is a hemolytic
anemia caused by autoantibodies that react at temperatures < 37°
C (usually < 30° C [86° F]). The disease is associated with
infections (especially mycoplasmal pneumonias or infectious
mononucleosis) and lymphoproliferative states; about 1/2 of cases
are idiopathic, which is the common form in older adults. It
presents clinically as an acute (most commonly associated with
viral or bacterial infections) or chronic (most commonly
idiopathic) hemolytic anemia. Other cryopathic symptoms or signs
may be present (eg, acrocyanoses, Raynaud's phenomena,
cold-associated occlusive changes).
Laboratory
features are those of extravascular hemolysis; rarely,
cases are fulminant and severe and associated with hemoglobinemia
and hemosiderinuria. Special features include clumping of RBCs on
the smear. Autoagglutination is often reflected by an increased
MCV and spurious low Hb recorded on automatic cell counting
instruments; hand warming of the tube and recounting result in
values significantly closer to normal. The anemia is usually mild;
Hb is generally > 7.5 g/dL. Cold antibodies are usually IgM
reacting against RBC membrane glycoproteins, termed "i"
to denote RBC characteristics of fetal cells or "I," the
membrane pattern of adult cells. Anti-i cold agglutinins occur
most commonly in infectious mononucleosis and malignant lymphoma
of the large cell type. Anti-I agglutinins occur in idiopathic
disease and after mycoplasmal pneumonia. In either case the IgM
activates and binds C3, and the degree of hemolysis relates to the
potency of this action and the temperature at which the reaction
occurs. The higher the temperature (ie, the closer it is to normal
body temperature) at which the antibody reacts with the RBC, the
greater the hemolysis. Because IgM easily washes off the cells,
the direct antiglobulin (Coombs') test usually identifies only C3
fixed to the cells. As expected, the hemolysis occurs largely in
the mononuclear phagocyte system of the liver.
Therapy is largely
supportive in acute cases, which are generally caused by
infection, because the anemia is self-limited. In chronic cases,
the anemia is generally mild. Treatment of the underlying disease
controls the anemia. In idiopathic chronic cases, the anemia is
generally mild (Hb, 9 to 10 g/dL) but may persist for life.
Avoidance of cold exposure is often helpful. Splenectomy is of no
value. Immunosuppressive drugs have only modest effectiveness.
Transfusions should be given cautiously with the blood warmed via
an on-line warmer. Autologous cell survival may be better than
that of transfused cells because the administered blood becomes
antibody-coated; autologous cells have already survived the
antibody effect on the RBCs, and effete C3 fragments (C3d) on
their surface do not affect RBC survival.
Paroxysmal
cold hemoglobinuria (PCH; Donath-Landsteiner syndrome) is
a rare type of cold agglutinin disease. Hemolysis occurs minutes
to hours after exposure to cold, which may even be localized (eg,
drinking cold water, washing hands in cold water). Intravascular
hemolysis is caused by an autohemolysin that binds to RBCs at low
temperatures and lyses them only after warming. The cold hemolysin
is a 7S IgG. PCH caused by a cold-activated autohemolysin occurs
in some patients with congenital or acquired syphilis, and
antisyphilitic therapy may cure the PCH. Most cases, however,
occur after a nonspecific viral illness or in otherwise healthy
patients.
Symptoms include
severe pain in the back and legs, headache, vomiting, diarrhea,
and passage of dark brown urine. Findings include hemoglobinuria,
mild anemia, and moderate reticulocytosis. The severity and
rapidity of development of the anemia vary widely. In some cases
it can be fulminant and represent an acute emergency.
Hepatosplenomegaly may be present. Mild hyperbilirubinemia may
follow the attack. The direct antiglobulin test is positive during
attacks but negative between them. The Donath-Landsteiner test
identifies the Donath-Landsteiner autoantibody, which has
specificity for the P antigen on the RBC.
Therapy consists of
strict avoidance of exposure to cold. Splenectomy is of no value.
Immunosuppressive drugs have been effective but should be
restricted to progressive or idiopathic cases.
