50079_laboratory testing in rheumatic disease

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Featured CME Topic: Arthritis

Laboratory Testing in the Rheumatic Diseases:

A Practical ReviewChristopher Lee Colglazier, MD, and Paul George Sutej, MD

Abstract: Laboratory testing for the rheumatic diseases can allow

for rapid diagnosis and appropriate management, while false-posi-

tive tests can lead to inappropriate management and unnecessary

concern for the patient. An evaluation of laboratory testing for rheu-

matic illnesses is discussed, including the well-known acute phase

proteins, the use of ANA in screening, and the newer antibodies

which may potentially allow for an earlier diagnosis. A thorough

history and examination are arguably the best screening tests. Cli-

nicians should be judicious in their use of laboratory testing, and

should only do so in an attempt to further refine the diagnosis.

Laboratory testing in the rheumatic illnesses can, for thepracticing clinician, result in perplexing data. Carefullyused, laboratory tests can be very specific and allow rapid

diagnosis and appropriate management. False-positive testing

may result in inappropriate management and unnecessary con-

cern. In this review, we attempt to circumvent this type of

problem. We review current thoughts on well-known acute

phase proteins to include the erythrocyte sedimentation rate(ESR) and C-reactive protein (CRP). We discuss the use of

the antinuclear antibody (ANA) in screening and specific

subserologies that often may lead to specific and accurate

diagnoses. Furthermore, we reflect on newer antibodies (to

include anti-cyclic citrullinated peptide [CCP] antibodies),

which have the potential of allowing earlier diagnosis and

possibly to promote more aggressive management for seem-

ingly more destructive disease. However, it should strongly

be argued that the best screening tests always remain the

standard tools available to the clinician: namely, an insightful

history and an appropriate examination. Testing should be

performed to further refine the differential diagnosis and not

simply to placate the anxious patients desire for early diag-

nosis. Both referring physicians and patients need to under-

stand that while an early, correct diagnosis is sought, this is

not always possible in the nonspecific and vague early symp-

toms so typical of many of the rheumatic diseases. The pres-

sure to provide early diagnosis often leads to indiscriminate

and cavalier ordering of these tests.

We will start by considering the more traditional and

cheaper mainstays of rheumatic tests: the ESR and CRP,

which form part of the acute phase response. These remain acornerstone of early screening and can prove useful in mon-

itoring disease activity.

Acute Phase ProteinsThe acute phase response is defined as the pathophysio-

logic activity accompanying inflammation. Proteins whose

plasma concentrations change by 25% during inflammatory

states are defined as acute phase proteins. There are a mul-

titude of such proteins, and the change in concentration can

either increase (as seen in ceruloplasmin, complement, CRP,

ESR, amyloid A, fibrinogen, alpha-1 antitrypsin, haptoglo-

bin, ferritin) or decrease (as seen in albumin, transferrin, tran-sthyretin). Many of the proteins are synthesized in the liver,

driven by cytokine levels such as interleukin (IL)-6. The clin-

ical combined effects of the acute phase response consist of a

spectrum from fever, increased cortisol release, and fatigue,

to anemia, cachexia, amyloidosis, impaired growth, and sep-

tic shock. Two of the most widely used acute phase labora-

tory tests by physicians are the ESR and CRP.

From the Section on Rheumatology and Clinical Immunology, Departmentof Internal Medicine, Wake Forest University School of Medicine, WakeForest, NC.

Reprint requests to Dr. Christopher Morris, 3 Sheridan Square, Kingsport,TN 37660. Email: [email protected]

Accepted January 21, 2004.

Copyright 2005 by The Southern Medical Association

0038-4348/05/9802-0185

Key Points

While laboratory testing can help with the diagnosisof rheumatic disease, overreliance on a lab result may

lead the clinician to an incorrect diagnosis.

Antinuclear antibodies are present in a number of con-

nective tissue diseases; while nearly all patients with

lupus are ANA-positive, the high number of false pos-

itives limits its utility as a screening test.

New tests, such as the cyclic citrullinated protein an-

tibody, may improve early identification of patients

with rheumatoid arthritis, particularly those with a

prognosis for a more aggressive disease.

Southern Medical Journal Volume 98, Number 2, February 2005 185


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Erythrocyte sedimentation rate

The ESR increases during an acute phase response. The

ESR is a measure of the distance that erythrocytes fall through

plasma in either a Westergren or Wintrobe tube over a period

of 1 hour (measured as mm/h). This is, in large part, influ-

enced by plasma proteins surrounding them, such as fibrin-ogen, which increase during an acute phase response. An

increased fibrinogen level has the effect of dissipating eryth-

rocyte repulsive forces, allowing closer aggregation (ie, rou-

leaux formation), thus causing erythrocytes to fall a longer

distance during a set amount of time. The Wintrobe method

uses a shorter tube and cannot quantify values over 50 to

60 mm/h.

Elevations in the ESR can be seen in inflammatory con-

ditions such as infection and in a large number of connective

tissue diseases such as systemic lupus erythematosus (SLE),

vasculitis, polymyalgia rheumatica, and rheumatoid arthritis.

However, the ESR is a very nonspecific marker. Since theESR is an indirect measurement of acute phase proteins, non-

inflammatory conditions (such as change in the morphology

and concentration of erythrocytes) or a change in activity or

concentrations of other plasma proteins (as in multiple my-

eloma) can elevate the ESR. The Westergren method uses

dilution to attempt to correct for the effects of anemia. The

change in ESR often lags behind an abrupt change in inflam-

matory conditions, sometimes decreasing by only 50% 1 week

after resolution of an inflammatory event. ESR also increases

with factors such as obesity, age, and female sex. Because of

the increase in ESR with age, it is important to adjust for age

when interpreting the normal range for the ESR. A general

rule of thumb for a normal ESR value in mm/h is as follows:

men age/2; women (age 10)/2.1

The experienced clinician is obviously aware of the co-

nundrum associated with using the ESR to screen for inflam-

matory arthritis or vasculitis. It is not unusual to see a very

active rheumatoid synovitis in the setting of a patient with a

normal ESR. On the other hand, an elevated ESR does not

necessarily imply an underlying disease process. A common

clinical mistake is to ignore the patients age. Elderly patients

with diffuse musculoskeletal complaints are often screened

with an ESR and are inaccurately diagnosed with polymyal-gia rheumatica. Patients with polymyalgia rheumatica tend to

be white, closer to the age of 60 years, and present with

nonspecific complaints to include arthralgias of the shoulder

and pelvic girdle. The ESR tends to be dramatically elevated.

Intermediate values for the ESR need to be interpreted with

caution. Implicit in the diagnosis of polymyalgia rheumatica

is a fairly dramatic response to glucocorticoid therapy, usu-

ally within a 24- to 48-hour period. Therefore, there should be

some hesitation in diagnosing a 75-year-old woman with an

ESR of 52 with polymyalgia rheumatica, whose complaints

do not particularly fit the above-mentioned description and

whose response to glucocorticoid therapy is intermediate,

at best.

C-reactive protein

C-reactive protein is synthesized in the liver and increases

in the acute phase response. The role of CRP itself is complexand not fully understood. On one hand, it seems to have

pro-inflammatory effects, such as activating the classic com-

plement pathway and decreasing IL-6 receptor concentrations

in areas where IL-6 has anti-inflammatory effects.2 On the

other hand, it also has anti-inflammatory properties, such as

reducing neutrophil adhesion to endothelium.3 The general

rule of thumb for interpreting CRP levels in mg/dL is as

follows: 0.2 mg/dL normal; 0.2 mg/dL 1.0 mg/dL

indeterminate; and1 mg/dL inflammatory. A more ac-

curate rule for calculating normal CRP levels in patients age

25 to 70 is as follows: women (age/65) 0.7 mg/dL; men

(age/65)

0.1 mg/dL.

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In general, values 0.2 to 1.0 mg/dLare nonspecific and can be seen in instances such as cigarette

smoking and diabetes mellitus. Elevated levels are caused by

the same inflammatory conditions listed with the ESR; how-

ever, the rise and fall of the CRP is much more abrupt than

the ESR. Early elevation is seen within 4 hours of an event,

peaking at 24 to 72 hours. Infection is common with high

levels of CRP, with up to 85% incidence of bacterial infection

in patients with a CRP greater than 10 mg/dL.5

Acute phase proteins such as ESR and CRP are nonspe-

cific and in many cases, nonsensitive. They can be useful to

indicate the presence and severity of an inflammatory condi-

tion, which in the case of a connective tissue disease may

prompt therapy. In some cases, these values may be useful for

monitoring therapy to an extent. However, it should be

strongly argued that the patient is often an excellent judge of

response to therapy, and the dose of glucocorticoids in the

setting of polymyalgia should be titrated against the patients

perceived clinical response rather than the acute phase pro-

teins themselves. It should be remembered that normal values

are often seen in inflammatory conditions, and never rule out

the possibility of connective tissue diseases. In one study, up

to 10% of patients with moderate rheumatoid arthritis had a

normal ESR.6 Active SLE is also often seen in the setting of

normal ESR and CRP, and it has been suggested that up to

20% of patients with polymyalgia rheumatica can have anormal ESR, though this very concept itself is quite conten-

tious. Other conditions, such as malignancy, are seen with

elevated acute phase reactants. There is emerging evidence of

the association of CRP with cardiac events, and its clinical

usefulness is being determined and debated.

Antinuclear antibodies

Antinuclear antibodies are present in a wide array of

autoimmune diseases. When used correctly, they provide

valuable diagnostic and prognostic information; however, it

186 2005 Southern Medical Association


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must be kept in mind that their presence or absence alone can

neither rule in nor rule out any particular disease. The labo-

ratory method of performing ANA testing has varied over the

years, from the use of the lupus erythematosus (LE) cell test

in the 1940s to the current use of immunofluorescence. Along

with the change in laboratory methods, the performance char-

acteristics of the ANA have also changed. While the occur-rence of ANA-negative lupus has declined significantly

with more sensitive laboratory methods, the presence of ANA

in healthy patients has risen. It is therefore important to un-

derstand the predictive value of the ANA in different auto-

immune diseases.

The initial LE test of the 1940s was performed by incu-

bating a bare nucleus with a patients serum. A polymorpho-

nuclear leukocyte was then added, and if sufficient antibodies

in the patients serum had bound to the nucleus, opsonization

occurred. The LE cell is a polymorphonuclear leukocyte con-

taining a phagocytosed nucleus. The main method used now

is immunofluorescence. Hep-2 cells (derived from a humanepithelial tumor line) are incubated with a patients serum.

After washing, a fluoresceinated antibody is then added,

which binds to the patients antibodies bound to the nucleus.

Nuclear fluorescence can be seen through a fluorescence mi-

croscope, along with a staining pattern.

A precise characterization of the performance of the ANA

is difficult to define. Varying laboratory methods, as well as

studies in differing patient subsets, have yielded a wide range

of sensitivity and specificity. Solomon et al7 critically re-

viewed available published data on ANA to calculate a

weighted average of performance characteristics. These re-

sults, listed in Table 1, provide the sensitivity, specificity, andlikelihood ratios (LR) of the ANA in different disease states.

Most notable is the high sensitivity in SLE, in which a neg-

ative ANA makes the probability of SLE unlikely (negative

LR 0.11). However, a positive ANA result is less helpful,

with a positive predictive value of only 11% (positive LR

2.2). Given the low specificity, an ANA should only be sent

in patients suspected of SLE and should be interpreted in the

context of the clinical presentation. One reason for such poor

specificity for SLE is that the ANA is commonly seen in

other disease states such as other connective tissue diseases

and chronic infections (ie, hepatitis C), can be associated with

multiple medications, and can be seen in healthy patients. The

ANA is found in 5 to 10% of patients without evidence of

connective tissue disease, increasing in prevalence with age

and in patients of relatives with rheumatic disease. The ANA

is also seen in many other autoimmune disease states not

associated with a connective tissue disease, such as autoim-mune hepatitis, primary autoimmune cholangitis, primary bil-

iary cirrhosis, primary pulmonary hypertension, Graves dis-

ease, and Hashimoto thyroiditis.

The low sensitivity and specificity of the ANA in other

connective tissue diseases, shown in Table 1, makes the ANA

a weak test for ruling in or ruling out polymyositis, dermato-

myositis, rheumatoid arthritis, and Sjgren syndrome. Al-

though not useful for ruling in scleroderma, it can be helpful

to rule it out, with a sensitivity of 85% (negative LR 0.27).

Of particular note is the marginal likelihood ratio when used

to distinguish primary from secondary Raynaud, in which the

ANA is not very helpful. In the instance of a patient withRaynaud, an ANA should only be sent if a diagnosis such as

scleroderma is suspected, but not as a screening tool.

The staining pattern of an ANA is important and is de-

termined by the target antigen. Table 2 lists the different

patterns and their association with different disease states. In

general, ANA patterns are not sensitive or specific and have

been supplanted by other tests discussed in this paper. Pat-

terns can also be unreliable, as pattern recognition is some-

what operator dependent and can also change at different

dilutions.

ANA titers can be important in the interpretation of the

ANA test. In one study of 125 individuals with a positiveANA but no other evidence of a connective tissue disease,

titers of greater than 1:40 were seen in 32%, greater than 1:80

were seen in 13%, and greater than 1:320 were only seen in

3% of patients.8 All patients in this study had a negative

dsDNA. Although useful in making a diagnosis, the ANA

titer is not useful to predict disease activity. It is a common

mistake for patients to have ANAs repeated again and again,

as if they will become negative with treatment or as if titers

will decline. Patients themselves often become somewhat en-

trapped in how high is my ANA titer today? It should

Table 1. Performance characteristics of antinuclear antibodies in connective tissue diseases

Disease Sensitivity SpecificityPositive

likelihood ratioNegative

likelihood ratio

Systemic lupus erythematosus 93% 57% 2.2 0.11

Scleroderma 85% 54% 1.86 0.27

Polymyositis/dermatomyositis 61% 63% 1.67 0.61

Rheumatoid arthritis 41% 56% 0.93 1.06

Sjogren syndrome 48% 52% 0.99 1.01

Secondary Raynaud 64% 41% 1.08 0.88



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always be remembered that a particular laboratory may incur

an error. If the diagnosis of SLE is strongly suspected, and an

ANA test is negative, we would argue that this test be re-

peated either at the same laboratory or at some other labora-

tory. On the other hand, a low-positive titer is simply that and

nothing else. It is somewhat inappropriate to screen a 57-

year-old woman with arthralgias with an ANA test who sim-

ply has generalized osteoarthritis. There should be a high

index of suspicion of a connective tissue disease process be-

fore using this laboratory test as a screening predictor. Spe-

cifically, if the patient is a young woman of childbearingpotential who has a rash and joint pain, the ANA test would

be quite appropriate. If positive, specific subserologies can

then be ordered.

Types of ANAs

Laboratory tests can also assess the presence of antibod-

ies to specific nuclear proteins, which will be discussed be-

low. While specificity for most of these tests is high, sensi-

tivity markedly decreases. In contrast to the ANA, which has

a high sensitivity and can be useful for ruling out (but not

ruling in) SLE, the tests listed below in Table 3 have a high

specificity and are most useful for ruling in (but not ruling

out) certain connective tissue diseases.

Anti-ssDNA and anti-dsDNA antibodies

Anti-DNA antibodies are most commonly associated with

SLE. Antibodies to single stranded DNA (anti-ssDNA) are

very nonspecific, clinically not very useful, and therefore will

not be discussed. Antibodies to double stranded DNA (anti-

dsDNA), however, are of particular interest. Kavanaugh and

Solomon9 critically reviewed available published data on an-

ti-dsDNA to calculate a weighted average of performance

characteristics. Based on this review of anti-dsDNA data mea-

sured by three different laboratory methods, a sensitivity of

57.3%, and specificity of 97.4% was calculated (shown in

Table 3). The presence of anti-dsDNA is highly suggestive ofSLE (positive LR 16.3); however, its absence does not

significantly decrease post test probability of disease (nega-

tive LR 0.49). Anti-dsDNA has been associated with more

severe disease, including renal involvement. In general, it is

debated whether the levels correlate with disease activity, but

it does appear that at least in some patients this is the case.912

Laboratory tests can either be done by radioimmunoassay

(Farr method) or indirect immunofluorescence (Crithidia Lu-

cilia). Despite the high specificity for SLE, it should be remem-

bered that although exceedingly rare, anti-dsDNAhasbeen found

in other rheumatologic ailments. Occasionally, patients receiv-

ing minocycline, etanercept, infliximab, and penicillamine havealso been found to have positive serologies.

Anti-Sm, anti-U1-RNP, anti-histone antibodies

The anti-Smith (anti-Sm) antibody binds to a series of

nonhistone proteins complexed with small nuclear RNAs, the

complex being referred to as small nuclear ribonucleoprotein

particles/proteins (snRNP). These snRNPs are involved in the

Table 2. Antinuclear antibody patterns and associated

diseasesa

Antinuclearantibodypattern Associated antigen Associated disease

Homogeneous DNA histone complex(ribonucleoprotein,nucleosome)

SLE, drug-induced lupus,other diseases

Peripheral/rim DNA, nuclear envelopeantigens

SLE, autoimmune hepatitis

Speckled Smith, RNP, SS-A, SS-B,Scl-70, centromere, RNApolymerase II and III

SLE, MCTD, Sjogren,PSS, other diseases

Nucleolar Nucleolar RNA, RNApolymerase I

Diffuse systemic sclerosis,hepatocellular carcinoma

Centromeric C entromeres Limited cutaneous systemicsclerosis

aSLE, systemic lupus erythematosus; MCTD, mixed connective tissue dis-

ease; PSS, progressive systemic sclerosis.

Table 3. Performance characteristics of specific antinuclear antibodiesa

Antigen Associated condition Sensitivity Specificity Positivelikelihood ratio Negativelikelihood ratio

anti-dsDNA Ab Systemic lupus erythematosus 57% 97% 16.3 0.49

anti-Smith (Sm) Ab Systemic lupus erythematosus 2530 High* * *

anti-Ro/SS-A Ab Sjogren, SCLE, neonatal lupus syndrome 870 87 * *

anti-La/SS-B Ab Sjogren, SCLE, neonatal lupus syndrome 1640 94 * *

Scl-70 Systemic sclerosis 20% 100% 25 0.8

Anticentromere Limited cutaneous systemic sclerosis 65% 99.9% 650 0.4

Anti-U3-RNP Ab Scleroderma 12% 96% 3 0.92

aSCLE, subacute cutaneous lupus erythematosus.

*Precise data not available.



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machinery of messenger RNA splicing. Anti-Sm Ab is highly

specific and when present indicates SLE. However, it is only

seen in roughly 25 to 30% of SLE, and its absence is not

helpful in ruling out disease. Whereas anti-dsDNA antibodies

can become undetectable with quiescent disease, anti-Sm may

remain elevated. Anti-U1-RNP Ab is another type of snRNP

antibody; however, it is associated with mixed connectivetissue diseases consisting of a combination of SLE, sclero-

derma, and polymyositis. As the definition of mixed connec-

tive tissue disease involves anti-U1-RNP Ab, performance

characteristics cannot be calculated. Anti-histone antibodies

are found in 95% of drug-induced lupus. However, the pres-

ence of anti-histone antibodies does not verify drug-induced

lupus; as most patients with the presence of these antibodies

do not go on to develop symptoms. For example, anti-histone

Abs occur in 80% of patients taking procainamide, but most

will not have development of drug-induced lupus.

Anti-Ro/SS-A and anti-La/SS-B antibodies

Anti-Ro/SS-A and anti-La/SS-B antibodies recognize

cellular proteins complexed with small nuclear RNAs, and

are found mainly in association with Sjgren syndrome and

SLE, although they can be found in other conditions such as

scleroderma, polymyositis, mixed connective tissue disease,

and rheumatoid arthritis. Anti-Ro/SS-A Abs are found in 50%

of patients with SLE, being associated with photosensitivity

(subacute cutaneous lupus), cutaneous vasculitis, and inter-

stitial lung disease. They are also found in 75% of patients

with primary Sjgren syndrome but in only 10 to 15% of

those with secondary Sjgren.13 These antibodies are also

associated with neonatal lupus syndrome and congenital heart

block. Approximately 80% of babies born with congenital

heart block have the presence of anti-Ro/SS-A or anti-La/

SS-B in the mother, even in cases without a connective tissue

disease. However, of all mothers with the presence of anti-

Ro/SS-A or anti-La/SS-B, less than 1% will be associated

with neonatal lupus syndrome or congenital heart block. An-

ti-Ro/SS-A and anti-La/SS-B Abs have also been associated

with patients who fit the criteria for SLE but have a negative

ANA (ANA-negative lupus); however, as mentioned earlier,

this is becoming less common. Anti-Ro/SS-A and anti-La/

SS-B antibodies are also seen in 0.1 to 0.5% of healthy adults.

Anti-centromere, anti-Scl-70, anti-U3-RNP

antibodies

Antibodies against topoisomerase I, or Scl-70, have been

found in roughly 20% of patients with diffuse systemic scle-

rosis.14 Although the sensitivity is low, specificity approaches

100%. When present, the diagnosis of scleroderma is almost

certain. The presence of anti-Scl-70 Abs are also associated

with an increased risk of radiographic pulmonary fibrosis,

abnormal pulmonary function tests, and diffuse cutaneous

involvement. When compared with controls of primary

Raynaud, Scl-70 has a sensitivity of 28%, and specificity of

98% (positive LR 10, negative LR 0.7).14 It is therefore

useful to rule in (but not out) scleroderma in a patient with

Raynaud. Anti-centromere antibodies are associated with lim-

ited cutaneous systemic sclerosis (formerly CREST). Com-

pared with healthy control subjects, the specificity for CREST

is very high (99.9%), although the sensitivity is low (65%).14

When present, they almost certainly rule in disease, although

their absence does not make disease significantly less likely.

The use of anti-centromere Ab to distinguish CREST from

diffuse systemic sclerosis is less useful (positive LR 3.9,

negative LR 0.5). Anti-centromere Ab can also be useful in

ruling out CREST in a patient presenting with Raynaud (neg-

ative LR 0.2 when comparing CREST with primary

Raynaud), although not as useful for ruling in scleroderma in

this instance (positive LR 3.5). Antifibrillin nucleolar (An-

ti-U3-RNP) antibodies are present in approximately 12% of

patients with scleroderma. Although their sensitivity is low,

their specificity is high (96%), and when present, they can beassociated with muscle, small bowel, renal, and cardiac in-

volvement, as well as pulmonary hypertension.15,16

Rheumatoid Arthritis

Rheumatoid factor

Rheumatoid factor (RF) is commonly used in the diag-

nosis of rheumatoid arthritis. RF is an antibody against the Fc

portion of IgG, but in clinical practice is measured as IgM.

The role of RF in disease is not clear but may be related to the

binding by RF on B-cells to immunoglobulins attached to

antigens for antigen presentation, resulting in amplification ofthe humoral response. The sensitivity of RF for rheumatoid

arthritis varies, depending on the patient population. RF is

associated with more severe disease with greater extra-artic-

ular features. It then would make sense that sensitivity of RF

in studies of more severe RA is higher than in those with mild

disease. In general, the sensitivity of RF for RA is around 50

to 85%, increasing over time, as some people with rheuma-

toid arthritis are initially RF negative only to later serocon-

vert. However, RF alone cannot make a diagnosis of rheu-

matoid arthritis, as roughly 5% of a young healthy population

can be RF positive, and this rate increases with age. Although

most associated with rheumatoid arthritis, RF can also beseen in Sjgren syndrome, mixed connective tissue disease,

mixed cryoglobulinemia, SLE, and polymyositis, as well as

nonrheumatic disorders such as chronic infections, inflamma-

tory disorders, and malignancy.

Only 50% of early rheumatoids demonstrate RF positiv-

ity. Furthermore, around 15% of patients with RA never have

RF positivity. Therefore, this test should only be ordered

where the diagnosis of RA is strongly suspected: namely, in

the setting of obvious joint swelling, synovitis, or effusions.

Another setting would be the finding of erosive changes ra-

diologically. As previously suggested, screening the elderly



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somewhat randomly with rheumatoid factors in the setting of

minimal joint findings may indeed yield false-positive re-

sults. The consequence of these false-positive investigations

result in great patient fear and anxiety and lead to expensive,

extensive and inappropriate investigations.

Anti-CCP antibodies

Anti-cyclic citrullinated peptide (anti-CCP) antibodies

have been around for decades but have recently been gaining

popularity. These were first described as markers for RA in

1964. It was because of very exacting technical requirements

that anti-CCP antibodies never gained wide-spread accep-

tance, despite their specificity for RA. Some research sug-

gests that citrullinated extracellular fibrin in synovium is a

significant autoantigen involved in the immune response in

rheumatoid arthritis. It has similar sensitivity for RA (50 to

85%) but higher specificity (90 to- 95%).17 Its clinical use-

fulness is still evolving; however, these antibodies are quiteobviously potentially important surrogate markers for diag-

nosis of RA. They may also be useful in the prognosis of this

condition. They are as sensitive and seemingly more specific

than IgM RF, particularly in early prognosis, but also in fully

established disease. An argument has been made that their

usefulness may indeed be in predicting the eventual evolution

into RA, particularly when found in the setting of an undif-

ferentiated inflammatory arthropathy, which is not an unusual

presentation that faces a clinician. These antibodies have been

detected in healthy individuals before the onset of clinical RA

and seem to also occur in the setting of erosive disease.

Other Antibodies

Antineutrophil cytoplasmic antibodies

Antineutrophil cytoplasmic antibodies (ANCA) are di-

rected against several neutrophil cytoplasmic components.

They are often used in the evaluation of vasculitis, specifi-

cally Wegener granulomatosis, microscopic polyarteritis, and

Churg-Strauss syndrome. The two main target antigens are

proteinase 3 and myeloperoxidase, which are located in the

azurophilic granules of neutrophils and the peroxidase-posi-

tive lysosomes of monocytes. The two basic staining patterns

are cytoplasmic (c-ANCA) and perinuclear (p-ANCA).ANCA-associated conditions can be either c-ANCA or p-

ANCA; however, some diseases have a predilection for one

pattern. The c-ANCA pattern is highly sensitive for Wegner

granulomatosis, seen in more than 90% of active disease. The

antigen involved is proteinase 3, and an ELISA assay for this

can be done individually. Even though sensitive, the speci-

ficity of a c-ANCA is low, in one series roughly 50%.18

Using ELISA for proteinase 3 gives a higher specificity. The

p-ANCA pattern is directed against several proteins including

myeloperoxidase and elastase, and is much less sensitive and

specific. It is most commonly associated with microscopic

polyarteritis (70%)19 but can also be seen in pauci-immune

glomerulonephritis without extrarenal disease (80%)20 and

Wegener. Similarly to proteinase 3, using the ELISA test for

myeloperoxidase is more specific for vasculitis. Either ANCA

pattern is commonly seen in Churg-Strauss (50%),21 inflam-

matory bowel disease, rheumatoid arthritis, other connective

tissue diseases, and drug-induced illness (such as with pro-pylthiouracil). Although the pattern is helpful to establish

vasculitis, both c-ANCA and p-ANCA can be seen in micro-

scopic polyarteritis and Wegener granulomatosis; therefore,

the result alone does not make the distinction. It can, how-

ever, be useful in distinguishing microscopic polyarteritis and

Wegener granulomatosis from polyarteritis nodosa, which is

rarely ANCA-positive.

The usefulness of ANCA can particularly be seen in the

clinical situation in which a biopsy can be circumvented. An

open lung biopsy is associated with significant morbidity and

mortality. If a c-ANCA returns strongly positive, the diagno-

sis of Wegener granulomatosis would seem to be more so-lidified and may indeed avoid a costly and dangerous biopsy.

Similarly, renal biopsy may be avoided.

Myositis-specific antibodies (anti-Jo 1, anti-Mi2,

anti-SRP, anti-MAS)

Although autoantibodies are rarely used in the initial

diagnosis of an inflammatory myopathy, once the diagnosis

has been established they can give information as to disease

manifestation. The most common is anti-synthetase (Jo-1),

which can be seen in interstitial lung disease and mechanics

hands. Anti-Mi2 can be seen in dermatomyositis and is cor-

related with a good prognosis. Anti-SRP is associated withcardiac disease and poor response to medical therapy. Anti-

MAS can be seen in alcoholic rhabdomyolysis.

ConclusionIn the above review, we have outlined the dichotomy

offered by the laboratory in terms of the usefulness in diag-

nosis and prognosis of rheumatologic diseases. We clearly

believe that these laboratory tests will never circumvent the

need for a detail-oriented history and insightful, specific clin-

ical examination. An appropriate differential diagnosis fol-

lowed by thoughtful screening should prove rewarding both

to the clinician and the patient. The scare factor in terms offalse-positive diagnoses may be avoided and inappropriate,

expensive, subsequent investigations bypassed. On the other

hand, appropriate screening with early diagnosis and treat-

ment should indeed prove rewarding.

References1. Sox HC Jr, Liang MH. The erythrocyte sedimentation rate: guidelines

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Anything that is too stupid to be spoken is sung.Voltaire


50079_laboratory testing in rheumatic disease

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