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Use and Interpretation of Rheumatologic Tests: A Guide for Clinicians

1996; Elsevier BV; Volume: 71; Issue: 4 Linguagem: Inglês

10.4065/71.4.391

1942-5546

Kevin G. Moder,

Autoimmune Bullous Skin Diseases

In recent years, several new autoantibody tests have been developed and are being used in the field of rheumatology, including the antineutrophil cytoplasmic antibody (ANCA) and myositis-specific antibodies such as anti-Jo1. Positive test results for ANCAs reveal one of two basic staining patterns: cytoplasmic (c-ANCA) or perinuclear (p-ANCA). The Jol anti-body test is often helpful at the time of diagnosis of a new case of idiopathic inflammatory myopathy. Herein this article reviews the clinical utility of the new tests in conjunction with the established autoantibody tests including antinuclear antibodies and extractable nuclear antibodies. Both the antinuclear antibody and extractable nuclear antibody tests are helpful in diagnosing connective tissue diseases. Before the results of any of these tests can be interpreted, the physician must consider the sensitivity, specificity, and negative and positive predictive values. Positive results must be analyzed in the clinical context and in relationship to other autoantibody test results. In recent years, several new autoantibody tests have been developed and are being used in the field of rheumatology, including the antineutrophil cytoplasmic antibody (ANCA) and myositis-specific antibodies such as anti-Jo1. Positive test results for ANCAs reveal one of two basic staining patterns: cytoplasmic (c-ANCA) or perinuclear (p-ANCA). The Jol anti-body test is often helpful at the time of diagnosis of a new case of idiopathic inflammatory myopathy. Herein this article reviews the clinical utility of the new tests in conjunction with the established autoantibody tests including antinuclear antibodies and extractable nuclear antibodies. Both the antinuclear antibody and extractable nuclear antibody tests are helpful in diagnosing connective tissue diseases. Before the results of any of these tests can be interpreted, the physician must consider the sensitivity, specificity, and negative and positive predictive values. Positive results must be analyzed in the clinical context and in relationship to other autoantibody test results. Because of the increasing emphasis on primary-care medicine, physicians are frequently ordering and analyzing tests previously used by subspecialists. Herein this article focuses on the utility of the tests commonly used to assess patients with or thought to have rheumatic disease and the subsequent interpretation of the results. Before obtaining any test, the physician must have a clear indication of and an anticipated response to the outcome of the test. The indication for a test usually fits into one of the following categories: (1) to screen for a particular disease, (2) to help confirm a specific diagnosis, (3) to evaluate disease activity, (4) to assess for target organ involvement, and (5) to monitor for drug toxicity. If a test will not alter the patient's diagnosis, prognosis, or therapy, it probably is un&x00AD;necessary. Before interpreting a test result, the physician must consider the sensitivity, specificity, and positive and negative predictive values of a test Sensitivity refers to the proportion of patients with a disease who have a positive test result, and it indicates the accuracy of a test in detecting the disease. Specificity refers to the proportion of patients without the disease who have a negative test result, and it indicates the accuracy of a test in identifying those without the disease. The positive and negative predictive values of a test vary with the prevalence of the disease in the population tested. As the prevalence of the disease decreases in the population, it becomes less likely that a patient with a positive test result actually has the disease and more likely that the test represents a false-positive result. The positive predictive value is the probability that a patient with a positive test result actu&x00AD;ally has the disease, whereas the negative predictive value is the probability that a person with a negative test result does not have the disease.1Huiley SB Cummings SR Designing Clinical Research: An Epidemiologic Approach. Williams & Wilkins, Baltimore1988Google Scholar One of the hallmarks of autoimmune disorders, including systemic lupus erythematosus (SLE) and many other connective tissue diseases (CTDs), is the formation of autoanti&x00AD;bodies.2von Muhlen CA Tan EM Autoantibodies in the diagnosis of systemic rheumatic diseases.Semin Arthritis Rheum. 1995; 24: 323-358Abstract Full Text PDF PubMed Scopus (557) Google Scholar The antinuclear antibody (ANA) test is widely available and uses an indirect immunofluorescence technique that detects antibodies that bind to various nuclear antigens. The ANA test is very sensitive for SLE; more than 95&x0025; of patients with SLE have positive results (Table 1). It is not specific, however, for SLE, and positive test results can occur with other CTDs, infections, malignant lesions, and various other pathologic conditions, as well as in otherwise healthy persons. Therefore, as with all rheumatologic tests, positive results must be interpreted in the clinical context and in relationship to other autoantibody test results. A positive test result is reported both as a particular staining pattern and as a titer. The four commonly recognized staining patterns are as follows: homogeneous, speckled, diffuse, and anti-centromere. Emphasis on the staining pattern has diminished during the past several years because of recognition of considerable overlap between patterns and diseases and the availability of more specific autoantibody tests (Table 1). Lower titer values (less than 1:160) often have minimal clinical significance and may not be related to the patient's symptoms.Table 1Autoantibodies Detected in Patients With Connective Tissue Diseases*ANA = antinuclear antibody; CAH = chronic active hepatitis; c-ANCA = cytoplasmic-staining anti-neutrophil cytoplasmic autoantibody; CHB = congenital heart block; CREST = calcinosis cutis, fiaynaud's phenomenon, esophageal dysfunction, iderodactyly, and felangiectasia; CTD = connective tissue diseases; GN = glomerulonephritis; IBD = inflammatory bowel disease; MCTD = mixed CTD; p-ANCA = perinuciear-staining ANCA; PSS = progressive systemic sclerosis; RA = rheumatoid arthritis; RF = rheumatoid factor; SLE = systemic lupus erythematosus; SS = Sjogren's syndrome; WG = Wegener's granulomatosis.AutoanlibodyFrequency of occurrenceCommentsANASLE, 95%; many other CTDSensitive but not specific for CTDDouble-stranded DNASLE, 30-70%; CAHSpecific but not sensitive for SLE; levels correlate with disease activitySmSLE, 90%; idiopathic SLE, >50%; RA and Felly's syndrome, occasionallyNot specific but sensitive for drug-induced SLEAnti-centromereCREST syndrome, >80%Staining pattern on ANA, relatively specific and sensitive for CRESTAnti-Scl 70PSS, 26-76%Specific but not sensitive for PSSc-ANCAActive WG, >90%Titers tend to vary with disease activityp-ANCAWG, 10%; other vasculitis, GN, IBDLess specific and sensitive for WG than is c-ANCARFRA, 80%; SS, 50%; other CTDHigh levels tend to correlate with severe RA* ANA = antinuclear antibody; CAH = chronic active hepatitis; c-ANCA = cytoplasmic-staining anti-neutrophil cytoplasmic autoantibody; CHB = congenital heart block; CREST = calcinosis cutis, fiaynaud's phenomenon, esophageal dysfunction, iderodactyly, and felangiectasia; CTD = connective tissue diseases; GN = glomerulonephritis; IBD = inflammatory bowel disease; MCTD = mixed CTD; p-ANCA = perinuciear-staining ANCA; PSS = progressive systemic sclerosis; RA = rheumatoid arthritis; RF = rheumatoid factor; SLE = systemic lupus erythematosus; SS = Sjogren's syndrome; WG = Wegener's granulomatosis. Open table in a new tab In SLE, the pattern and titer of ANA results are variable and do not necessarily reflect disease activity (that is, the titer of the ANA does not necessarily increase with more active disease). The ANA test is most useful in helping to diagnose CTDs. It has much less utility for monitoring patients. For example, in SLE, many other laboratory variables including the erythrocyte sedimentation rate, complement, and anti-double-stranded DNA (anti-dsDNA) antibodies are more useful in assessing disease activity. Furthermore, clinical factors including patient symptoms and physical examination findings such as synovitis and rash are much more important in assessing disease activity. ANA testing is commonly misused to "screen" for CTD when the diagnostic suspicion is low or to monitor disease activity in patients with a known CTD. Often, a patient with a well-established diagnosis of SLE or another CTD is hospitalized for an unrelated illness, and an ANA test is repeated for no clear purpose. Such reflexive use of ANA testing should be discouraged. A much more specific but less sensitive testing strategy for SLE is the finding of anti-dsDNA antibodies. The test can be performed by using several methods including the enzyme-linked immunosorbent assay technique. Increased levels of anti-dsDNA antibodies are evident in up to 70&x0025; of patients with SLE. The presence of anti-dsDNA antibodies tends to correlate with renal disease. Additionally, the level of anti-dsDNA antibodies tends to correlate with disease activity in some patients with SLE. The patient's history is important in that, if the dsDNA levels have been increased in the past with SLE flares, an increase may be clinically pertinent. If, however, the patient has had flares of SLE in the past without increased dsDNA levels, then this factor is less helpful. dsDNA antibodies are uncommon in other CTDs but can be present in autoimmune liver disease (chronic active hepatitis). dsDNA, as well as all other laboratory tests, must be interpreted in the clinical context of the patient. Antibodies to single-stranded DNA are nonspecific and have limited clinical utility. Anti-histone antibodies occur in up to 95&x0025; of cases of drug-induced SLE but may occur in more than 50&x0025; of cases of idiopathic SLE; thus, the presence of this antibody is occasionally less helpful than its absence. The appropriate clinical setting for drug-induced SLE involves a patient exposed to an agent known to cause drug-induced SLE, usually with a high-titer positive ANA, ab&x00AD;sence of antibodies to dsDNA, and clinical features of SLE but lacking central nervous system or renal manifestations. In this setting, the absence of anti-histone antibodies makes the diagnosis of drug-induced SLE less likely, but their presence would not confirm that the case is drug induced. Therefore, anti-histone antibodies are of limited use to the clinician. An anti-centromere staining pattern can be found on an ANA test in about 80&x0025; of patients with the limited variant of scleroderma, the so-called CREST (calcinosis cutis, Raynaud's phenomenon, esophageal dysfunction, sclerodactyly, and telangiectasia) syndrome. The test result is usually reported as positive or negative without a titer. This antibody can also be detected in up to 25&x0025; of patients with idiopathic Raynaud's phenomenon. Whether the presence of this antibody in a patient with Raynaud's phenomenon suggests that the CREST syndrome may develop is un&x00AD;clear.3Vlachoyiannopoulos PG Drosos AA Wiik A Moutsopoulos HM Patients with anticentromere antibodies, clinical features, diagnoses and evolution.Br J Rheumatol. 1993; 32: 297-301Crossref PubMed Scopus (77) Google Scholar Anti-Scl 70 antibodies can be identified in patients with progressive systemic sclerosis (PSS-diffuse scleroderma). These antibodies are directed against topoisomerase type I. The test result is also usually reported as positive or negative. The prevalence of anti-Scl 70 antibodies in patients with PSS varies widely from study to study and may vary with the patient's racial background. Estimates of their prevalence in PSS range from 26 to 76&x0025;.4Reveille JD Durban E Goldstein R Moreda R Arnett FC Racial differences in the frequencies of scleroderma-related autoantibodies.Arthritis Rheum. 1992; 35: 216-218Crossref PubMed Scopus (73) Google Scholar This antibody is often associated with more widespread skin disease and internal organ involvement than is the anti-centromere antibody. The anti-centromere and anti-Scl 70 tests are helpful in confirming a diagnosis of scleroderma, and they provide some prognostic information about a patient's potential future course inasmuch as the presence of anti-Scl 70 antibodies suggests a worse prognosis. Usually, these antibodies do not occur together in the same patient. Once a diagnosis of PSS or the CREST syndrome has been established, these tests do not need to be repeated. Of note, some patients with the CREST syndrome or with PSS may have neither antibody. Extractable nuclear antibodies (ENAs) may also be identified in patients with a CTD. Four autoantibodies, directed against ribonuclear proteins (RNA), can be detected with commonly available laboratory kits that often use an immunoblot technique. These antibodies are directed against several small nuclear ribonucleoproteins involved in RNA processing. In general, results of these tests are reported as either positive or negative without titers. These antibodies are helpful in diagnosis but are not useful in monitoring disease activity. The ENA panel includes a test for antibodies against the Sm antigen. Anti-Sm antibodies are very specific for SLE but lack sensitivity; they occur in about 30&x0025; of patients with SLE. The prevalence of these antibodies in young black women with SLE tends to be high, and these antibodies are seldom present with other diseases. Anti-Sm antibodies should not be confused with anti-smooth muscle antibodies detected in autoimmune liver disease (sclerosing cholangitis). Antibodies directed against another ENA, U1RNP, can be identified in many patients with CTDs. This antibody is neither specific nor sensitive for SLE but may be present in up to 40&x0025; of patients with SLE. Mixed CTD is a specific type of overlap syndrome in which patients may have features of several CTDs and by definition have a positive ENA for the U1RNP antibody.5Sharp GC Irvin WS Tan EM Gould RG Holman HR Mixed connective tissue disease-an apparently distinct rheumatic disease syndrome associated with a specific antibody to an extractable nuclear antigen (ENA).Am J Med. 1972; 52: 148-159Abstract Full Text PDF PubMed Scopus (1370) Google Scholar Patients may have an overlap syndrome without the presence of this antibody, but such patients do not have mixed CTD. Their condition is better described by the more general term "overlap CTD." Patients with SLE whose test results are positive only for U1RNP on the ENA panel and who lack dsDNA antibodies typically have a low frequency of nephritis, and they often have "scleroderma-like" features of disease such as Raynaud's phenomenon, esophageal hypomotility, and myositis. U1RNP antibodies tend to be detected more frequently in black patients than in white patients. Two other ENAs are the anti-SS-A/Ro and anti-SS-B/La. Both are frequently present together and commonly occur in patients with primary Sjögren's syndrome but may occur with other CTDs with or without associated primary Sjögren's syndrome. Anti-SS-A/Ro antibodies are found in about 25&x0025; of patients with SLE. Important clinical correlations include an association of this antibody with prominent skin disease, often in the setting of subacute cutaneous lupus. Children born to mothers with this antibody have an increased incidence of congenital heart block. Anti-SS-B/La antibodies, if present, usually accompany anti-SS-A/Ro antibodies. Anti-SS-B/La antibodies are less frequent in both Sjögren's syndrome and SLE than are anti-SS-A/Ro; they occur in about 10&x0025; of patients with SLE. Their presence as the sole autoantibody (except for ANA) in patients with SLE suggests a mild course of dis&x00AD;ease.6Swaak AJ Huysen V Smeenk RJ Antinuclear antibodies in routine analysis: the relevance of putative clinical associations.Ann Rheum Dis. 1993; 52: 110-114Crossref PubMed Scopus (25) Google Scholar Serum rheumatoid factors (RFs) are detected in about 80&x0025; of patients with rheumatoid arthritis (RA). They are frequently present in patients with Sjogren's syndrome and less commonly in patients with other CTDs.7Wolfe F Cathey MA Roberts FK The latex test revisited: rheumatoid factor testing in 8,287 rheumatic disease patients.Arthritis Rheum. 1991; 34: 951-960Crossref PubMed Scopus (105) Google Scholar Occasionally, they occur in patients without CTD, including those with chronic infections, especially subacute bacterial endocarditis and gammopathies. Most RFs are IgM autoantibodies directed against the "FC" portion of IgG immunoglobulins. Several methods are used for their detection, including an older latex fixation test, which is reported as a titer. New methods include nephelometric assays in which results are reported in international units. In general, high titers of RFs in patients with RA tend to correlate with severe articular disease and extra-articular manifestations, although this relationship is variable. Initially, some patients with RA may be seronegative and later become seropositive. Conversely, some seropositive patients may not have a measurable serum RF after receiving therapy. Although the RF has some prognostic value, it is not useful for assessing disease activity. Other measures of disease activity including patient symptoms, physical examination findings such as synovitis, and indicators of inflammation such as the erythrocyte sedimentation rate are better evidence of current disease activity than are serial measurements of serum RF. A common misuse of this test in patients with RA is similar to that of the ANA in patients with SLE. Patients with known seropositive RA are admitted to the hospital for unrelated illnesses, and serum RF tests are ordered reflexively. As with performing repeated ANA tests in a patient with SLE, this practice is wasteful and should be discouraged. Antineutrophil cytoplasmic antibodies (ANCAs) are recently discovered antibodies directed against several neutrophil cytoplasmic components.8Davies DJ Moran JE Niall JF Ryan GB Segmental necrotising glomerulonephritis with antineutrophil antibody: possible arbovirus aetiology?.BMJ. 1982; 285: 606Crossref PubMed Scopus (827) Google Scholar9Hall JB Wadham BM Wood CJ Ashton V Adam WR Vasculitis and glomerulonephritis: a subgroup with an antineutrophil cytoplasmic antibody.Aust N Z J Med. 1984; 14: 277-278Crossref PubMed Scopus (135) Google Scholar These antibodies are detected by using an immunofluorescence technique. Positive test results for ANCAs reveal one of two basic patterns of staining: cytoplasmic (c-ANCA) or perinuclear (p-ANCA). The c-ANCA indicates the presence of antibodies directed against proteinase 3. A positive c-ANCA test result is specific and sensitive for the presence of active Wegener's granulomatosis (WG); the test result is positive in more than 90&x0025; of patients with active WG. In many patients, the titer tends to correlate with the level of disease activity. With successful therapy, the ANCA titer usually decreases; however, the titer for active disease may vary widely from patient to patient. (For example, one patient with active disease may have a titer of 1:64 that decreases to 1:8 after treatment, whereas another patient with active disease may have a titer of 1:16&x00A0; that becomes negative after treatment.) Additionally, the time between a change in clinical disease activity and a change in ANCA titer may also vary widely from patient to patient.10Cohen Tervaert JW Huitema MG Hene RJ Sluiter WJ The TH van der Hem GK et al.Prevention of relapses in Wegener's granulomatosis by treatment based on antineutrophil cytoplastic antibody titre.Lancet. 1990; 336: 709-711Abstract PubMed Scopus (421) Google Scholar, 11van der Woude FJ Rasmussen N Lobatto S Wiik A Permin H van Es LA et al.Autoantibodies against neutrophils and monocytes: tool for diagnosis and marker of disease activity in Wegener's granulomatosis.Lancet. 1985; 1: 425-429Abstract PubMed Scopus (1421) Google Scholar, 12Kerr GS Fleischer TA Hallahan CW Leavitt RY Fauci AS Hoffman GS Limited prognostic value of changes in anti-neutrophil cytoplasmic antibody titer in patients with Wegener's granulomatosis.Arthritis Rheum. 1993; 36: 365-371Crossref PubMed Scopus (277) Google Scholar, 13Specks U Wheatley CL McDonald TJ Rohrbach MS DeRemee RA Anticytoplasmic autoantibodies in the diagnosis and follow-up of Wegener's granulomatosis.Mayo ClinProc. 1989; 64: 28-36Abstract Full Text Full Text PDF PubMed Scopus (246) Google Scholar In a patient with typical features of WG and a high titer cANCA, a tissue biopsy may not always be necessary to confirm the diagnosis. Histologic confirmation of WG by tissue biopsy is desirable, however, if affected tissue is amenable to sampling, and morbidity is low. It is also important in patients who have atypical clinical features. Although the c-ANCA test is useful in making the initial diagnosis of WG and in monitoring disease activity, treatment should not be based solely on the ANCA titer. As always, therapy should be based on the overall clinical context of the patient. The p-ANCA pattern is occasionally evident in patients with WG, but it is much less sensitive and much less specific for WG than is the c-ANCA pattern. The p-ANCA pattern can be found in patients with other vasculitides, glomerulonephritis, and, occasionally, inflammatory bowel disease.14Jennette JC Falk RJ ANCA—diagnostic markers or pathogenic agents?.Bull Rheum Dis. 1992; 41: 3-6PubMed Google Scholar, 15Plotz PH Dalakas M Leff RL Love LA Miller FW Cronin ME Current concepts in the idiopathic inflammatory myopathies: polymyositis, dermatomyositis, and related disorders.Ann Intern Med. 1989; 111: 143-157Crossref PubMed Scopus (253) Google Scholar The p-ANCA staining pattern has been termed "artefactual" because it appears only after cells have been fixed with alcohol. The antibodies that cause a p-ANCA pattern are directed against several proteins, most commonly myeloperoxidase or elastase. If the pattern is positive, an enzyme-linked immunosorbent assay can be done to determine whether the antibodies detected are directed against myeloperoxidase and in what quantity. The clinical usefulness of this titer is still uncertain. Recently, a new group of antibodies referred to as myositisspecific antibodies have been discovered that occur in up to 50&x0025; of patients with idiopathic inflammatory myopathy (IIM), including polymyositis and dermatomyositis.&x00A0;These antibodies allow better classification of patients in terms of both clinical features and prognosis (Table 2). Currently, the only clinically available antibody is the anti-Jo1. This antisynthetase antibody is directed against transfer-RNA histydyl synthetase and occurs in up to 30&x0025; of patients with IIM. It is associated with a constellation of clinical findings termed the "anti-synthetase syndrome," characterized by pulmonary fibrosis, often fever, Raynaud's phenomenon, and dry cracked skin on the hands ("mechanics' hands").16Moder KG Gaffey TA Matteson EL Idiopathic inflammatory myopathy of the antisynthetase (Jo-1) type associated with noncaseating granulomas.Arthritis Rheum. 1993; 36: 1743-1747Crossref PubMed Scopus (11) Google ScholarTable 2Overview of Myositis-Specific Antibodies*DM = dermatomyosilis; I1M = idiopathic inflammatory myopathy; MSA = myositis-specific antibodies; PM = poly my os ids.MSA%in HMClinical correlatesAnii-syntheiaset30-40Interstitial lung disease, fever, Raynaud's phenomenon, "mechanics' hands," arthritis. Jois the only currently available MSA in common clinical use. Can occur in PM and DM. Moderate response to treatment and intermediate prognosisAnti-Mi2SDM with V-sign rash, shawl-sign rash, cuticular overgrowth. Generally good response to treatment and relatively good prognosisAnti-SRP<5Cardiac disease, severe weakness. Poor response to treatment and poor prognosisAnti-MAS<1Alcoholic rhabdomyolysis. Good response to treatment and favorable prognosis† Includes Jol.* DM = dermatomyosilis; I1M = idiopathic inflammatory myopathy; MSA = myositis-specific antibodies; PM = poly my os ids. Open table in a new tab † Includes Jol. The Jo1 antibody test is often useful at the time of diagnosis of a new case of IIM. Its presence suggests that the patient may have an aggressive disease course including pulmonary involvement and may require aggressive initial therapy. Survival of patients with this antibody is decreased in comparison with that of patients with myositis who do not have this antibody.17Love LA Leff RL Fraser DD Targoff IN Dalakas M Plotz PH et al.A new approach to the classification of idiopathic inflammatory myopathy: myositis-specific autoantibodies define useful homogeneous patient groups.Medicine. 1991; 70: 360-375Crossref PubMed Scopus (837) Google Scholar Performing this test in patients with newly diagnosed or highly suspected IIM, especially those with pulmonary symptoms, is appropriate. Occasionally, the Jol 1 test may also be useful in the setting of a patient with an undefined CTD and interstitial lung disease. Because the J01 antibody has a low sensitivity for IIM, it should not be used in patients in whom clinical suspicion of IIM is low. Selecting the appropriate autoantibody test in patients with suspected rheumatologic disorders should be guided by the clinical setting. Before ordering the test, the physician should have a clear indication of and anticipated response to the test result. Usually, the best approach is to begin with sensitive tests, and if the results are positive, tests that are specific may be obtained to help confirm the diagnosis. For example, if SLE is suspected on the basis of clinical features such as inflammatory arthritis, serositis, and skin rash, an ANA test should be ordered. If the result is positive, then additional, more specific but less sensitive, autoantibody tests such as ENA (assessing for anti-Sm) or dsDNA may be done.