The determination of antinuclear antibodies (ANA) is of central importance for the clinical diagnosis of connective tissue diseases, which are systemic inflammatory diseases with a chronic course of disease. Connective tissue diseases exhibit overlapping symptomatic features that render an accurate diagnosis difficult.

The Phadia EliA ANA CTD screen wells are coated with human recombinant U1RNP (RNP70, A, C),SS-A/Ro (60 kDa, 52 kDa), SS-B/La, Centromere B, Scl-70, Jo-1, Fibrillarin, RNA Pol III, Rib-P, PM-Scl, PCNA, Mi-2 proteins, Sm proteins and native purified DNA. This ANA screen is more specific than traditional IF ANA methods, which show a high false positive rate.

A positive ANA CTD screen requires the specific quantification of the antibodies listed above: ds-DNA and the individual anti-extractable nuclear antigen (ENA) antibodies.

For the diagnosis of systemic lupus erythematosus (SLE), dsDNA antibodies are considered to be a highly specific marker representing one of the diagnostic criteria for SLE (ACR criteria). More than 90 % of sera from patients with active SLE contain dsDNA antibodies. Additionally, the determination of dsDNA antibodies is a tool to monitor the clinical course of a defined SLE patient, because a clear-cut relationship exists between anti-dsDNA titre and disease activity, in particular renal involvement. Sm antibodies offer a highly specific, but comparatively insensitive, clinical marker for SLE. Indeed, their presence constitutes one of the revised ACR criteria for diagnosis, even though their overall prevalence ranges from 20 % to 30 % in SLE. U1-snRNP antibodies typically appear in both SLE and mixed connective tissue disease (MCTD, Sharp Syndrome).

In MCTD, the presence of U1-snRNP antibodies is required for diagnosis, whereas they occur in only 30 to 40 % of SLE patients. Detection of SS-A/Ro antibodies is of interest and significance for the clinical diagnosis of SLE (prevalence 40-50%) and Sjögren's syndrome (prevalence 60-75% for primary Sjögren's syndrome). They have been reported to occur in tight association with certain disease subsets, such as subacute cutaneous LE, neonatal lupus erythematosus or vasculitis in Sjögren's syndrome. As anti-SS-A/Ro may be the only antibody present in many patients with SLE or Sjögren's syndrome, failure to measure antiSS-A/Ro leaves a diagnostic void which cannot be filled by other tests. SS-B/La antibodies are the serological hallmark of Sjögren's syndrome but a small proportion of patients remains anti-SS-B/La negative. La antibodies are found in 6-15 % of sera from SLE patients. Here, they are associated with a lower prevalence of dsDNA antibodies and renal disease.

Although a strong association of neonatal lupus erythematosus (NLE) with Ro antibodies was recognized first, the majority of mothers with babies with NLE are now known to have La antibodies as well.

CENP antibodies are found in 70-90 % of patients with CREST Syndrome, a limited form of scleroderma with a comparatively favourable prognosis. However, they may also occur in Raynaud's phenomenon and primary biliary cirrhosis (about 10-20 %).

Antibodies against Scl-70 are characteristic and specific for scleroderma (particularly the diffuse form; frequency up to 70%). Jo-1 antibodies can be found as markers in dermatomyositis/polymyositis (prevalence of about 25%), but also in patients with polymyositis overlap syndrome. They are associated with interstitial pneumonitis (in the context of myositis) and occur in a far smaller proportion of children with myositis than of adults. Patients with Jo-1 antibodies tend to have a severe form of the disease with a tendency to relapse and a poorer prognosis. Fibrillarin antibodies produce a nucleolar pattern in immunofluorescence. They occur in less than 15% of patients with scleroderma and seem to be associated with internal organ involvement including pulmonary hypertension, myositis, and renal disease. The presence of fibrillarin antibodies in diseases other than scleroderma and their clinical relevance requires further investigation. RNA polymerase III antibodies are highly specific for scleroderma and are here more frequent in patients with diffuse cutaneous scleroderma than in those with limited cutaneous scleroderma. Among patients with diffuse cutaneous involvement, RNA polymerase III antibody was the most common antibody detected (35-45%).

Antibodies against Ribosomal P proteins react with the specific ribosomal proteins (P0, P1 and P2). These autoantibodies occur in SLE during active disease and are associated with neuropsychiatric, renal and hepatic involvement. They are found in 23% of SLE patients.

Autoantibodies to the polymyositis/scleroderma (PM-Scl) complex were the first antinucleolar antibodies identified in systemic sclerosis. Anti-PM-Scl are associated with a specific form of scleroderma; indeed, only 2% of the patient population with scleroderma, but 24% of the patients with myositis-scleroderma overlap syndrome produce these antibodies. They correlate with a benign course of disease and a positive response to steroid therapy. Antibodies against PCNA (proliferating cell nuclear antigen) occur in 2 to 10% of SLE patients but seem to be not very specific for SLE as it was found in 12.3% of hepatitis B and 18.7% of hepatitis C patients, respectively.

Autoantibodies targeting the Mi-2 nuclear antigen represent one of the serologic hallmarks of polymyositis/dermatomyositis, with a diagnostic sensitivity and specificity of approximately 4-18% and 98-100%, respectively. They are strongly associated with dermatomyositis with a frequency of up to 31%.

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Preparation of Patient: No special preparation.

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Reflex testing: The Phadia EliA ANA CTD wells are coated with human recombinant U1RNP (RNP70, A, C),SS-A/Ro (60 kDa, 52 kDa), SS-B/La, Centromere B, Scl-70, Jo-1, Fibrillarin, RNA Pol III, Rib-P, PM-Scl, PCNA, Mi-2 proteins, Sm proteins and native purified DNA. A positive ANA CTD screen will lead to analysis of specific ds-DNA antibodies and ENA antibody typing.

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