Serological Testing Recommendations for Interstitial Lung Disease

Core ILD Panel for All Newly Identified ILD Patients

The American Thoracic Society, European Respiratory Society, Japanese Respiratory Society, and Latin American Thoracic Association recommend that all patients with newly detected ILD undergo a core serological panel (ANA by immunofluorescence, rheumatoid factor, anti‑CCP antibodies, C‑reactive protein, and erythrocyte sedimentation rate) to screen for underlying connective‑tissue disease. This is described as a “motherhood statement,” indicating an essential standard‑of‑care recommendation. 1, 2
Expert consensus (majority of panelists) supports routine use of the core panel in every new ILD case, regardless of clinical suspicion. 1

The same expert panel advises adding muscle enzymes (creatine phosphokinase, myoglobin, aldolase) and a comprehensive set of myositis‑specific antibodies (antisynthetase antibodies such as Jo‑1, anti‑MDA5, anti‑Mi‑2, anti‑NXP2, anti‑TIF1‑γ, anti‑SRP, anti‑HMGCR, anti‑SAE, anti‑U1RNP, anti‑PM/Scl75/100, anti‑Ku) to the work‑up when clinical features suggest inflammatory myopathy. 1

For patients in whom systemic sclerosis is a differential diagnosis, the panel should include anti‑Scl‑70/topoisomerase‑1, anti‑centromere, anti‑RNA polymerase III, anti‑U1RNP, anti‑Th/To, anti‑PMScl, U3 RNP (fibrillarin), and anti‑Ku antibodies. 1

When Sjögren syndrome is considered, testing should incorporate anti‑SSA/Ro and anti‑SSB/La antibodies. 1

In the setting of suspected vasculitis, anti‑neutrophil cytoplasmic antibodies (ANCA) should be obtained. 1

Approximately 20 % of interstitial lung diseases in Europe and the United States are associated with autoimmune rheumatic diseases, underscoring the need for systematic serologic screening. 3
In many connective‑tissue‑disease‑associated ILDs, pulmonary involvement may be the first, dominant, or sole manifestation of the underlying autoimmune condition. 1
Patients often do not fulfill standard rheumatologic classification criteria at initial presentation, making serology a critical early diagnostic tool. 1
A diagnosis of idiopathic pulmonary fibrosis requires exclusion of alternative causes, including CTD‑related ILD. 1

Only a small minority of panelists advocate ordering the full extended panel for every patient at baseline; the prevailing approach is to perform the core tests universally and add disease‑specific assays case‑by‑case based on clinical signs and symptoms. 1
Referral to a rheumatologist is reserved for patients with positive clinical manifestations, abnormal serologies, or atypical features for idiopathic pulmonary fibrosis (e.g., female sex, age < 60 years). 1

The American Thoracic Society recommends performing an autoimmune panel to investigate for underlying connective tissue disease (CTD) in every patient with interstitial pneumonia, as nearly 20% of ILDs are associated with autoimmune rheumatic diseases and pulmonary manifestations can be the first sign of rheumatic disease 4, 5
'Velcro' crackles on lung auscultation suggest lung fibrosis and should prompt thorough serological evaluation even if respiratory symptoms are minimal 4, 6
Skin changes including thickening, sclerodactyly, or rashes should prompt further evaluation for CTD 7
Joint inflammation or deformities are common in patients with CTD-ILD 4
Raynaud phenomenon and abnormal nail-fold capillaries are associated with increased risk of CTD-ILD 8

The European Respiratory Society recommends that all patients with interstitial pneumonia should undergo an autoimmune panel at initial evaluation 4, 9, 10
Antinuclear antibodies (ANA) by immunofluorescence - positive ANA significantly increases likelihood of CTD diagnosis (OR=14.4 when titer >1/320) 6
Rheumatoid factor (RF) is particularly important in suspected RA-ILD 6
Anti-cyclic citrullinated peptide (anti-CCP) has high specificity for RA-ILD 6
C-reactive protein (CRP) - elevated levels suggest active inflammation 7, 8, 6

Systemic sclerosis: ILD occurs in approximately 50% of patients 7, 11
Rheumatoid arthritis: Significant ILD prevalence, particularly with UIP pattern 7, 11
Sjögren syndrome: NSIP pattern predominates 7, 11
Mixed connective tissue disease: Multiple ILD patterns possible 7, 11
Idiopathic inflammatory myopathies: NSIP pattern most common 7, 11
Male sex, older age at disease onset, smoking history, and African-American ethnicity are additional risk factors for CTD-ILD 7, 8

Nonspecific interstitial pneumonia (NSIP) pattern is the main pattern in systemic sclerosis, inflammatory myopathies, and Sjögren syndrome 7, 11
Usual interstitial pneumonia (UIP) pattern is predominant in RA-ILD 7, 11
Decreased diffusing capacity for carbon monoxide (DLCO) aids early diagnosis 11, 9

ILD can present before, during, or after the diagnosis of rheumatic disease 4, 11
Irreversible loss of lung function can be silent and significant in early stages, making early detection essential for informed treatment decisions and improved prognosis 4, 11