Measurements of Autoimmunity
The presence of certain autoantibodies have
diagnostic value for SLE. The most specific
tests are those that detect high levels of
The most common
and specific tests for autoantibodies and
other elements of the immune system are
Antinuclear Antibody (ANA)
A screening test for ANA is standard in
assessing SLE because it is positive in close
to 100% of patients with active SLE.
However, it is also positive in 95% of
patients with mixed connective tissue
disease, in more than 90% of patients with
systemic sclerosis, in 70% of patients with
primary Sjogren's syndrome, in 40-50% of
patients with rheumatoid arthritis, and in
5-10% of patients with no systemic rheumatic
Patients with SLE tend to have high
titers of ANA. False-positive results are
found during chronic infectious diseases,
such as subacute bacterial endocarditis,
tuberculosis, hepatitis, and malaria.
sensitivity and specificity of ANA
determinations depend on the technique used.
Anti-Sm is an immunoglobulin specific
against Sm, a ribonucleoprotein found in
the cell nucleus.
This test is highly specific
for SLE; it is rarely found in patients with
other rheumatic diseases.
30% of patients with SLE have a positive
Anti-nDNA is an immunoglobulin specific
against native (double-stranded) DNA. This
test is highly specific for SLE; it is not found
in patients with other rheumatic diseases.
Sixty to eighty percent of patients with
active SLE have a positive anti-nDNA test.
For many patients with anti-nDNA, the
titer is a useful measure of disease activity.
The presence of anti-nDNA is associated
with a greater risk of lupus nephritis.
Anti-Ro(SSA) and Anti-La(SSB)
These immunoglobulins, commonly found
together, are specific against RNA proteins.
Anti-Ro is found in 30% of SLE patients
and 70% of patients with primary Sjogren's
Anti-La is found in 15% of lupus
patients and 60% of patients with primary
Sjogren's syndrome. Anti-Ro is highly
associated with photosensitivity; both are
associated with neonatal lupus.
Complement proteins constitute a serum
enzyme system that helps mediate inflammation.
Complement components are triggered
into an activated form by such immunologic
events as interaction with immune complexes.
Complement components are identified by
numbers (C1, C2, etc.).
of C1q, C2, and C4, although rare, are
commonly associated with SLE.
A test to
evaluate the entire complement system is
called CH50. The most commonly measured
complement components are the serum level
of C3 and C4.
These tests are particularly
useful in evaluating kidney involvement and
in monitoring the disease over time.
Erythrocyte Sedimentation Rate (ESR) and C-Reactive Protein (CRP)
Tests for ESR and CRP are nonspecific tests
to detect generalized inflammation.
are generally increased in patients with active
lupus and decline when corticosteroids or
NSAIDs are used to reduce inflammation.
APLs are autoantibodies that react with
Recent data indicate that
APLs recognize a number of phospholipidbinding
plasma proteins (e.g., prothrombin,
B2-glycoprotein I) or protein-phospholipid
complexes rather than phospholipids alone.
APLs are present in 30--40% of lupus patients.
A positive APL test plus the presence of
arterial and venous thrombosis and thromboembolism
or recurrent fetal deaths or
thrombocytopenia is called APL syndrome.
APL syndrome affects about a third of lupus
patients with APLs (10-15% of all lupus
patients). APLs and APL syndrome may also
occur in patients without lupus (primary
APL syndrome). APLs are detected in the
following three types of laboratory assays.
Certain blood tests for syphilis may be
falsely positive in lupus patients. Chronically
false-positive VDRL or rapid plasma reagin
(RPR) tests may occur in patients with lupus.
Cardiolipin, a phospholipid, is a component
of the antigenic mixture used in these assays.
More specific tests for syphilis, such as the
fluorescent treponemal antibody-absorbed
(FTA-ABS) and microhemagglutinationTreponema
pallidum (MHA-TP) assays, are
almost always negative in lupus patients
Anticardiolipin Antibody (ACA)
Sensitive enzyme-linked immunoabsorbent
assays (ELISA) using cardiolipin as the
putative antigen are commonly used to
In patients with APL syndrome,
most antibodies detected in anticardiolipin
ELISAs are directed against cardiolipin-bound
Lupus anticoagulants are APLs that inhibit
certain coagulation tests, such as the activated
partial thromboplastin time (aPTT), dilute
Russell viper venom time (dRVVT), and
kaolin clotting time (KCT).
antibodies act as anticoagulants in these
laboratory assays, they are not clinically
associated with hemorrhage, but with
thrombosis and other manifestations of the
Most lupus anticoagulant
antibodies are directed against prothrombin
or B2-glycoprotein 1.
Source: National Institutes of Health, U.S.Dept of Health and Human Services