Blood Tests for Investigating Interstitial Lung Disease (ILD)

Initial Evaluation

A complete blood count with differential is recommended to assess for inflammatory markers and rule out other causes, according to Pulmonology 1
C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) are used to evaluate inflammatory activity, as suggested by the American Journal of Respiratory and Critical Care Medicine and European Respiratory Review 2, 3
Serum creatinine, transaminases, γ-glutamyltransferase, and alkaline phosphatases are assessed to evaluate organ function and rule out other causes, as recommended by European Respiratory Review 3

Antinuclear antibodies (ANA) by immunofluorescence are tested, with positive ANA significantly increasing the likelihood of CTD diagnosis (OR=14.4 when titer >1/320), according to the American Journal of Respiratory and Critical Care Medicine 2
Rheumatoid factor (RF) is particularly important in suspected RA-ILD, as suggested by the American Journal of Respiratory and Critical Care Medicine and European Respiratory Review 2, 3
Anti-cyclic citrullinated peptide (anti-CCP) has high specificity for RA-ILD, according to the American Journal of Respiratory and Critical Care Medicine and European Respiratory Review 2, 3
For suspected systemic sclerosis, anti-Scl-70/topoisomerase-1 is associated with increased ILD risk, as recommended by the American Journal of Respiratory and Critical Care Medicine and Pulmonology 2, 4
For suspected inflammatory myopathies, myositis-specific antibodies, including anti-synthetase antibodies (Jo-1 and others), are strongly associated with ILD, according to the American Journal of Respiratory and Critical Care Medicine and Pulmonology 2, 4
For suspected Sjögren's syndrome, anti-SSA/Ro and anti-SSB/La antibodies are tested, as suggested by the American Journal of Respiratory and Critical Care Medicine and European Respiratory Review 2, 3

Relying solely on negative serologies to rule out CTD-ILD is a pitfall, as some patients with CTD-ILD may not initially meet standard rheumatologic diagnostic criteria, according to the American Journal of Respiratory and Critical Care Medicine 2
Failing to repeat serological testing is a pitfall, as some autoantibodies may develop over time, so consider repeat testing if clinical suspicion remains high despite initial negative results, as recommended by Pulmonology and Arthritis and Rheumatology 1, 5
The presence of 'velcro' crackles on lung auscultation should prompt thorough serological evaluation even if respiratory symptoms are minimal, according to Pulmonology 1