Fw: Laboratory Tests Used To Diagnose Lupus

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From: " Kathi " <pureheart@...>

Sent: Tuesday, October 01, 2002 9:44 AM

Subject: Laboratory Tests Used To Diagnose Lupus

> Laboratory Tests Used To Diagnose Lupus

>

> Lupus is characterized by abnormalities in many laboratory test results.

> These

> abnormalities are different for every patient and vary significantly

> during the

> course of a patient's disease. The serial evaluation of an individual's

> tests

> along with the physician's observations and the patient's history

> determine

> the diagnosis of SLE, its course, and the treatment regimen. All

> laboratory

> values must be interpreted in light of the patient's present status,

> other

> correlating laboratory test results, and coexisting illnesses. This

> article briefly

> describes the major tests used to diagnose and evaluate SLE and provides

>

> information on their rationale and clinical usefulness. Nurses and other

> health

> professionals should consult rheumatologists, manuals of laboratory and

> diagnostic tests, or hospital clinical laboratory departments for

> further

> information on possible interpretations of results from these tests and

> their

> implications for SLE.

>

> Tests for Blood Cell Abnormalities

> Blood cell abnormalities often accompany SLE. People suspected of having

>

> lupus are usually tested for anemia, leukopenia, and thrombocytopenia.

>

> Anemia: Tests for anemia include those for hemoglobin, hematocrit, and

> red

> blood cell (RBC) count. In addition, the levels of iron, total

> iron-binding

> capacity, and ferritin may be tested. At any time during the course of

> the

> disease, about 40% of patients with SLE will be anemic. The anemia may

> be

> caused by iron deficiency, GI bleeding, medications, or autoantibody

> formation to RBCs. When first diagnosed, about 50% of patients have a

> form

> of anemia in which the concentration of hemoglobin and the size of the

> RBCs

> are normal. This is called normochromic- normocytic anemia, or " anemia

> of

> chronic disease. " Autoimmune hemolytic anemia, with a positive Coombs

> test,

> is much less common.

>

> Leukopenia and Thrombocytopenia: Abnormalities in the white blood cell

> (WBC) and platelet counts are an important indicator of SLE. Leukopenia,

> a

> decrease in the number of WBCs, is very common in active SLE and is

> found

> in 15-20% of patients. Thrombocytopenia, or a low platelet count, occurs

> in

> 25-35% of patients with SLE.

>

> Measurements of Autoimmunity

>

> The presence of certain autoantibodies have diagnostic value for SLE.

> The

> most specific tests are those that detect high levels of these

> autoantibodies.

> The most common and specific tests for autoantibodies and other elements

> of

> the immune system are listed first.

>

> 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 Sjögren's syndrome, in 40-50% of patients with

> rheumatoid arthritis, and in 5-10% of patients with no systemic

> rheumatic

> disease. 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. The

> sensitivity and

> specificity of ANA determinations depend on the technique used.

>

> Anti-Sm: 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. However,

> only

> 30% of patients with SLE have a positive anti-Sm test.

>

> Anti-nDNA: 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 Sjögren's syndrome. Anti-La is

>

> found in 15% of lupus patients and 60% of patients with primary

> Sjögren's

> syndrome. Anti-Ro is highly associated with photosensitivity; both are

> associated with neonatal lupus.

>

> Complement: 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.).

> Genetic deficiencies 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. Levels are generally increased in patients with active

> lupus and

> decline when corticosteroids or NSAIDs are used to reduce inflammation.

>

> Antiphospholipid Antibodies (APLs): APLs are autoantibodies that react

> with phospholipids. Recent data indicate that APLs recognize a number of

>

> phospholipid-binding plasma proteins (e.g., prothrombin, ß2-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 thrombo- embolism 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.

>

> Syphilis Serology: 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 microhemagglutination-Treponema pallidum (MHA-TP) assays, are almost

>

> always negative in lupus patients without syphilis.

>

> Anticardiolipin Antibody (ACA): Sensitive enzyme-linked immunoabsorbent

> assays (ELISA) using cardiolipin as the putative antigen are commonly

> used

> to detect APLs. In patients with APL syndrome, most antibodies detected

> in

> anticardiolipin ELISAs are directed against cardiolipin-bound

> ß2-glycoprotein I.

>

> Lupus Anticoagulant: Lupus anticoagulants are APLs that inhibit certain

> coagulation tests, such as the activated partial thromboplastin time

> (aPTT),

> dilute viper venom time (dRVVT), and kaolin clotting time (KCT).

>

> Although the antibodies act as anticoagulants in these laboratory

> assays,

> they are not clinically associated with hemorrhage, but with thrombosis

> and

> other manifestations of the APL syndrome. Most lupus anticoagulant

> antibodies are directed against prothrombin or ß2-glycoprotein I.

>

> Tests for Kidney Disease

>

> Several tests can be done to assess a patient for kidney disease.

>

> Measurement of Glomerular Filtration Rate: The glomerular filtration

> rate

> is a measure of the efficiency of kidneys in filtering blood to excrete

> metabolic products. Typically this is done by collecting a 24-hour urine

>

> sample for measurement of creatinine clearance. Impairment of renal

> function

> by lupus nephritis results in reduced levels of creatinine clearances.

>

> Urinalysis: Urinalysis can indicate the presence or extent of renal

> disease.

> For example, proteinuria can be a reliable indicator of renal disease.

> The

> presence of RBCs, WBCs, and cellular casts, particularly red cell casts,

> in the

> urine also indicates renal disease.

>

> Measurement of Serum Creatinine Concentration: Creatinine is a waste

> product of muscle metabolism that is excreted by the kidney. Loss of

> renal

> function as a consequence of lupus nephritis causes increases in serum

> levels

> of creatinine. The concentration of creatinine in the serum can be used

> to

> assess the degree of renal impairment.

>

> Kidney Biopsy: Kidney biopsy can be used to determine the presence of

> immune complexes and the presence, extent, and type of inflammation in

> the

> glomeruli. Diagnosis of the extent and type of inflammation may help to

> determine a treatment program for lupus.

>

> Credits

>

> National Arthritis and Musculoskeletal and Skin

> Diseases

> Information Clearinghouse

> NIAMS/National Institutes of Health

> 1 AMS Circle

> Bethesda, MD 20892-3675

>