Read The Lupus Book: A Guide for Patients and Their Families, Third Edition Online
Authors: Daniel J. Wallace
difficult to diagnose.
Unfortunately, the history and physical examination are not enough to diagnose
or manage lupus, so yes, we must draw blood. Blood testing can make a dif-
ference. It is essential in order to diagnose a disease correctly and to gauge the patient’s response to therapy. And specific tests are employed to monitor the
safety of medications that might be used to treat the disease. Finally, some lupus patients have specific complications that can be diagnosed only by blood testing.
This chapter offers an overview of the tests doctors order and why.
WHAT IS CONSIDERED ‘‘ROUTINE’’ LAB WORK?
When a patient arrives at an internist’s or family practitioner’s office for a
general medical evaluation, this usually calls for what doctors refer to as
‘‘screening laboratory tests.’’ In other words, by obtaining a blood count, urine test, and blood chemistry panel, abnormalities can be detected in 90 percent of individuals with serious medical problems. This is the starting point of the
workup. All the studies listed below are inexpensive and mostly automated; they can be performed within a matter of hours and do not require special expertise.
Most large medical offices are equipped to perform these tests on the premises.
A
complete blood count
(CBC) is the most commonly performed laboratory
test in the United States. It analyzes red cells, white cells, and platelets. Patients with systemic lupus can have low red blood cell counts or be anemic as a result of chronic disease, bleeding, from lupus medication, autoimmune hemolytic anemia (breakdown of red blood cells due to antibodies), or a vitamin deficiency.
The white blood cell count can be high due to steroid therapy or inflammation
or low from active lupus or a virus. Platelets are decreased when antibodies
attack platelets or when the bone marrow is not making enough of them. Most
patients with active SLE have an abnormal CBC.
Blood chemistry
panels consist of anywhere from 7 to 25 tests that evaluate a variety of parameters, including blood sugar, kidney function (BUN, creatinine), liver function (AST, ALT, bilirubin, alkaline phosphatase, GGT), electro-
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lytes (sodium, potassium, chloride, bicarbonate, calcium, phosphorus, magne-
sium), lipids (cholesterol, triglycerides, HDL, LDL), proteins, (albumin, total protein), thyroid function (T3, T4, TSH), and gout (uric acid). Occasionally,
chemistry panels include additional studies (amylase for pancreatic function,
LDH for hemolysis, iron levels, etc.), which are also inexpensive and can be
done by request. Any of these tests may be abnormal in SLE patients; the reader is referred to the index to find specific discussions that address their questions.
Urinalysis
is a useful screen for kidney involvement and urinary tract infections. All but 1 percent of lupus patients with clinically significant renal disease will have an abnormal urinalysis.
Several additional blood tests relevant to SLE also are inexpensive, readily
available, and commonly ordered by rheumatologists. These consist of the
creatine phosphokinase (CPK)
, which screens for muscle inflammation; a
Westergren sedimentation rate
or
C-reactive protein (CRP)
, which quantitates levels of inflammation; and the
prothrombin time (PT)
or
partial thromboplastin time
(PTT)
, which are clotting tests and may be prolonged in those who have the lupus anticoagulant.
ROUTINE ANTIBODY PANELS AND SCREENS
Very few doctors’ offices are equipped to do reliable antibody screening. Most
community and hospital laboratories are capable of performing these tests, but
the lack of a national standard, inexperienced technicians, and failure to double and triple check results impair their accuracy. Autoantibodies can be tested for anywhere, but if the results are positive, they should be confirmed in a reliable rheumatology laboratory. Such facilities include university-based teaching medical centers, private facilities with a national reputation for special expertise in rheumatology (e.g., Rheumatology Diagnostic Laboratory), or certain large national lab networks (e.g., Mayo Clinic Laboratories). The reader is referred to Chapter 6 for a detailed discussion of all the tests listed below.
What does autoantibody screening consist of and how does your doctor in-
terpret these results? Most of the centers listed above have what is called a
‘‘reflex panel.’’ Simply stated, a doctor orders an ANA, and if it is positive, another eight to ten antibody and immune determinations are automatically obtained.
The
antinuclear antibody
(
ANA
) is the cornerstone of rheumatic disease screening. As mentioned earlier, some ten million Americans have a positive
ANA but fewer than one million have SLE. Patients with other rheumatic dis-
eases such as rheumatoid arthritis and scleroderma as well as healthy relatives of patients with autoimmine diseases can have a positive ANA. The ANA can
also become positive with aging, certain viral infections, or as a result of taking
Must We Draw Blood?
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specific prescription drugs. However, less than 3 percent of patients with SLE
are ANA-negative.
Practically speaking, interpretation of the ANA test is guided by a few prin-
ciples. First, high levels of this antibody (greater than 1:1280 or greater than 30
International Units) are usually associated with a real rheumatic disease. Second, whereas rimed patterns are specific for lupus, homogeneous ANA patterns generally correlate with SLE, while speckled patterns are seen in SLE and with
other autoimmune processes. Even though ANA levels decrease with clinical
improvement, this correlation is weak at best and not a reliable gauge of the
disease process. Also, different laboratories use varying standards for ANA.
Therefore, a reading of 1:640 from one laboratory may be the same as 1:320
from another.
Anti-double-stranded DNA
antibodies are rarely present in patients who do not have SLE. They are found in half of those with the disease and represent
one of the more specific parameters for diagnosis and for following severe in-
flammation or organ involvement. Occasionally, healthy patients have low-level
positive tests. If performed by a Farr or ELISA method, anti-DNA can be quan-
titated, and its values reflect clinical disease activity; the values are higher with flares, and they decrease with improvement.
Serum
complement
measures levels of a protein that is consumed during the inflammatory process. Along with anti-DNA, complement components C3, C4,
or CH50 are the most reliable parameters for following serious disease activity.
Low complement levels imply active inflammation. A few patients with genetic
complement deficiencies always have low complements, and in them these de-
terminations are not useful in following disease activity.
Levels of
anti-Ro (SSA)
or
anti-La (SSB)
are of no value in following disease activity. These tests are either positive or negative. Positive tests confirm the presence of an autoimmune problem that may not even be symptomatic and
suggest that the doctor look for Sjo¨gren’s syndrome and subacute cutaneous
lupus rashes while also asking the patient about severe sun-sensitivity. Young
women with these antibodies should be warned about the possibility of having
a baby with neonatal lupus or congenital heart block (Chapters 22 and 30).
Similarly, levels of
anti-Sm
or
anti-RNP
are of little value in following patients.
These tests are also either positive or negative. Anti-Sm is of no importance in following disease activity but is extremely specific and useful in confirming the diagnosis of SLE. Anti-RNP in high levels suggests that the patient may have
mixed connective tissue disease (MCTD) and at low levels supports the diag-
nosis of SLE. The levels rarely change.
Since one-third of patients with lupus have antiphospholipid antibodies that
may lead to blood clots, miscarriages, and strokes, most rheumatologists screen for these antibodies. As discussed in Chapter 21, the antiphospholipid antibodies
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Where And How Can The Body Be Affected By Lupus?
can be tricky to detect, and a given patient may have only one of several possible autoantibodies. The most commonly ordered screen consists of an
RPR
or
VDRL
(syphilis test),
anticardiolipin antibody
, and the
lupus anticoagulant
. Further testing is necessary only if the patient’s history includes a blood clot and these initial screenings are negative.
Additional tests that are frequently done are screening for the rheumatoid
factor and serum protein electrophoresis. The
rheumatoid factor
test is positive in 80 percent of rheumatoid arthritis patients and 20 to 30 percent of those with SLE. High levels of rheumatoid factor with low levels of ANA suggest that a
diagnosis of rheumatoid arthritis should be considered as opposed to SLE.
Anti
cyclic citrullinated peptide
(CCP) antibodies, if present, are fairly specific for rheumatoid arthritis and is only present in 5 percent with SLE.
Serum protein
electrophoresis
is an inexpensive test for blood protein abnormalities; if a broad band of gamma globulin is found, it confirms an autoimmune process.
ADDITIONAL ANTIBODY SCREENS AND TESTS
Occasionally, additional blood testing is indicated to sort out peculiar or unusual symptoms. These tests are expensive, take longer to perform, and should be sent only to laboratories that have special immunologic expertise.
Antihistone antibodies
are found in nearly all patients with drug-induced lupus but are not specific, since at least half of all lupus patients have them.
Antineuronal antibodies
in the spinal fluid are usually specific for central nervous system lupus. In the blood, these antibodies are positive in 20 percent of all patients with lupus, but high levels are found in 70 percent with nervous system activity.
Antiribosomal P
antibody may be positive in central nervous system disease and may correlate with SLE psychosis.
Coombs’ antibody
testing screens for autoimmune hemolytic anemia, a serious blood complication of SLE.
The workup of antiphospholipid antibodies in patients with unusual manifes-
tations of the syndrome includes obtaining
protein C, protein S, antithrombin
3, Factor V Leiden mutation, anti-
β
-2 glycoprotein-1 antibodies, platelet antibody tests
, and
noncardiolipin antiphospholipid antibodies
. Sludging of the blood—which leads to dizziness, difficulty concentrating, and a sense of fullness—is evaluated by testing for
cryoglobulin
and
viscosity
, which, if present, imply that the blood is too thick. Systemic vasculitis atypical for lupus can be assessed with
anti-neutrophilic cytoplasmic antibody (ANCA)
testing. Similarly, lupus-like diseases such as rheumatoid arthritis scleroderma or autoimmune
myositis are characterized by the presence of numerous autoantibodies rarely
seen in SLE, such as
anti-PM-1, anti-Jo, anti-Scl-70
, or
anticentromere antibodies
. Lupus patients with high levels of the amino acid
homocysteine
may be at risk for cardiac disease and benefit from folic acid therapy.
The skin is often an affected area in lupus, with 60 to 70 percent of lupus
patients reporting some skin complaint. And there is a wide range of such com-
plaints. This chapter discusses how the skin is damaged in lupus and what it
looks like under the microscope. It reviews the classifications of skin disorders in lupus as well as their principal dermatologic features. A complete discussion of remedies used for skin disorders in lupus can be found in Part V, but specific interventions that are appropriate under special circumstances are mentioned
here.
HOW IS THE SKIN DAMAGED IN LUPUS?
The sun emits ultraviolet radiation in three bands known as A, B, and C. Only
the first two, ultraviolet A (UVA) and ultraviolet B (UVB), are directly harmful in lupus and are probably harmful to most of us. When these bands of ultraviolet light hit the skin of lupus patients, they damage deposits of DNA near the
surface of the skin. In some mouse lupus models, radiation to the top (epidermal) layer of the skin has resulted in the generation of denatured or altered DNA,
which researchers have found can lead to the formation of anti-DNA and result
in tissue damage. Also, ultraviolet light can induce the production of other antibodies—anti-Ro (SSA), anti-La (SSB), and anti-RNP—partly through altered
apoptosis in a skin cell known as a keratinocyte. Most patients who test positive for the anti-Ro (SSA) antibody are very sun-sensitive.
CLASSIFICATION OF CUTANEOUS LUPUS
Cutaneous
(which means relating to the skin) lupus can be broken down into three general categories:
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Where and How Can the Body Be Affected by Lupus?
1.
Acute cutaneous lupus erythematosus
. Almost all of these patients have active systemic lupus with skin inflammation.
2.
Subacute cutaneous lupus erythematosus (SCLE)
. This is a nonscarring rash that can coexist with both discoid and systemic lupus but may be a