Laboratory Evaluation and Autoantibody Testing in Systemic Sclerosis

Core Autoantibody Panel

ANA screening by indirect immunofluorescence on HEp‑2 cells detects antinuclear antibodies in > 90 % of patients with systemic sclerosis, establishing the first step of serologic diagnosis. 1
Anti‑centromere antibodies are strongly associated with limited‑cutaneous systemic sclerosis. 2
Anti‑topoisomerase I (anti‑Scl‑70) antibodies are linked to diffuse‑cutaneous disease and a higher prevalence of interstitial lung disease. [2][3]
Anti‑RNA polymerase III antibodies identify patients with diffuse‑cutaneous disease and confer an increased risk of scleroderma renal crisis and of associated malignancy. [4][5]

When the three core antibodies are negative or when an overlap syndrome is suspected, testing for less common autoantibodies (anti‑U3 RNP/fibrillarin, anti‑Th/To, anti‑PM/Scl‑75/100, anti‑U1 RNP, anti‑Ku) is recommended. [2][6]
In patients with inflammatory arthritis features, rheumatoid factor should be measured. 6
Anti‑citrullinated peptide antibodies are present in ≈ 3 % of systemic sclerosis patients who also meet criteria for rheumatoid arthritis. 6
For suspected lupus overlap, complement C3 and C4 levels, anti‑dsDNA antibodies, and anti‑Smith antibodies are indicated. [7][1]6
For suspected Sjögren‑type overlap, anti‑SSA/Ro and anti‑SSB/La antibodies should be assessed. 7

Blood pressure monitoring is essential for all early diffuse‑cutaneous patients, particularly those positive for anti‑RNA polymerase III, to detect impending scleroderma renal crisis. [4][5]
Baseline and periodic serum creatinine together with urinalysis are recommended for renal surveillance. 7
Alkaline phosphatase screening helps identify primary biliary cholangitis, which occurs in ~ 8 % of limited‑cutaneous patients, especially those with anti‑centromere antibodies. [2][6]
In early diffuse disease with suspected progressive interstitial lung disease, inflammatory markers (erythrocyte sedimentation rate, C‑reactive protein) and a complete blood count (noting thrombocytosis as a potential predictor of lung fibrosis) should be obtained. 3
Thyroid‑stimulating hormone and thyroid autoantibodies are advised when autoimmune thyroid disease is clinically suspected. [4][7]

The combination of Raynaud phenomenon, presence of systemic‑sclerosis‑specific autoantibodies, and/or characteristic nail‑fold capillaroscopy changes defines early or limited systemic sclerosis even in the absence of skin thickening. 8
Identification of anti‑RNA polymerase III positivity mandates aggressive blood‑pressure control because of the heightened renal‑crisis risk. [4][5]
Detection of anti‑topoisomerase I antibodies should trigger intensified pulmonary screening protocols to monitor for interstitial lung disease. [2][3]

In patients who test positive for anti‑PM/Scl antibodies, interstitial lung disease (ILD) occurs in ≈ 86.7 % of cases and can be the only clinical manifestation in about 26.7 % of patients, underscoring the antibody as a strong risk factor for pulmonary involvement【9】.

High‑resolution chest CT should be performed as the primary imaging modality for all anti‑PM/Scl‑positive individuals to detect ILD early, given its high prevalence in this subgroup【9】.
Pulmonary function testing (spirometry with diffusion capacity for carbon monoxide, DLCO) is recommended to establish a baseline and to identify restrictive physiology that may indicate early ILD【9】.