How is pulmonary fibrosis diagnosed?

How to Diagnose Pulmonary Fibrosis

The diagnosis of pulmonary fibrosis requires high-resolution computed tomography (HRCT) as the cornerstone imaging modality, combined with systematic exclusion of secondary causes, and integration of clinical, radiological, and when necessary, pathological findings through multidisciplinary discussion. 1, 2

Initial Clinical Assessment

Key Clinical Features to Identify

• Progressive exertional dyspnea developing over more than 6 months, typically in patients over 50-70 years of age 1
• Bibasilar inspiratory "velcro" crackles on auscultation, present in >80% of cases and appearing early in disease 1
• Nonproductive dry cough refractory to antitussive agents 1
• Finger clubbing in 25-50% of patients 1
• Absence of fever (fever suggests alternative diagnosis) 1
• No extrapulmonary manifestations (weight loss and fatigue may occur, but joint symptoms or rashes suggest connective tissue disease) 1

Mandatory Diagnostic Workup

High-Resolution CT Imaging

Obtain HRCT immediately with thin collimation (≤2 mm slice thickness), without contrast, including both inspiratory and expiratory images 2

Look for definite UIP pattern (all four features required): 1

• Subpleural and basal predominance
• Reticular abnormality
• Honeycombing with or without traction bronchiectasis
• Absence of features inconsistent with UIP

Features that exclude UIP pattern (any one of these): 1

• Upper or mid-lung predominance
• Peribronchovascular predominance
• Extensive ground-glass opacity (more than reticular abnormality)
• Profuse micronodules in upper lobes
• Multiple discrete cysts away from honeycombing areas
• Diffuse mosaic attenuation/air-trapping
• Consolidation in bronchopulmonary segments

Exclude Secondary Causes

Perform comprehensive exposure history to identify: 1, 2

• Occupational exposures (silica, asbestos, mineral particles)
• Inhaled organic antigens (hypersensitivity pneumonitis causes 47% of initially undiagnosed ILD) 2
• Pharmaceutical agents causing drug-induced ILD
• History of connective tissue disease symptoms

Obtain mandatory laboratory testing: 1

• Complete blood count, C-reactive protein, serum creatinine, liver enzymes
• Anti-nuclear antibodies, rheumatoid factor, anti-CCP antibodies (to exclude connective tissue disease)
• Anti-SSA, anti-SSB, anti-topoisomerase-1, anti-synthetase antibodies if ANA positive or clinical suspicion exists 1

Pulmonary Function Testing

Obtain baseline spirometry with FVC and DLCO to establish severity and provide prognostic information 1, 2

Perform 6-minute walk test with continuous oxygen saturation monitoring (oxygen saturation ≤88% at end of test predicts worse prognosis) 1, 2

Diagnostic Algorithm Based on HRCT Findings

If HRCT Shows Definite UIP Pattern

Do NOT perform surgical lung biopsy - the diagnosis can be established with clinical and radiographic features alone if secondary causes are excluded 2, 3

Proceed directly to multidisciplinary discussion to confirm idiopathic pulmonary fibrosis diagnosis 1

If HRCT Shows Possible UIP or Indeterminate Pattern

Consider bronchoalveolar lavage (BAL) when diagnosis is uncertain: 1, 4

• Increased neutrophils with some eosinophils suggests IPF
• Lymphocytosis >30% suggests alternative diagnosis (hypersensitivity pneumonitis, nonspecific interstitial pneumonia, sarcoidosis)

Consider video-assisted surgical lung biopsy if: 1, 2

• Patient is not at high surgical risk
• DLCO >25% after correction for hematocrit
• No severe hypoxemia at rest
• No severe pulmonary hypertension

Avoid surgical biopsy in patients with contraindications due to age, comorbidities, or disease severity 1

If HRCT Shows Pattern Inconsistent with UIP

Pursue alternative diagnoses through BAL, serologic testing, and potentially surgical biopsy 1, 4

Multidisciplinary Discussion Requirement

All cases must undergo multidisciplinary discussion involving pulmonologists, radiologists, and pathologists experienced in interstitial lung disease to integrate clinical, radiological, and pathological features 1, 2, 4

Refer complex cases to expert centers (reference or competence centers for rare lung diseases) when diagnosis remains uncertain 1, 4

Prognostic Assessment at Diagnosis

Assess prognosis using: 1, 2

• Severity of dyspnea
• FVC and DLCO values (DLCO 35-40% predicted indicates poor prognosis)
• Oxygen saturation at end of 6-minute walk test (≤88% indicates poor prognosis)
• Extent of honeycombing on HRCT
• Signs of pulmonary hypertension on echocardiography

Calculate GAP score (gender, age, physiology) for 1-, 2-, and 3-year survival estimates 1, 2

Common Diagnostic Pitfalls to Avoid

Do not diagnose IPF without adequate multidisciplinary discussion, as multiple conditions can mimic the disease 2, 4

Do not overlook connective tissue disease - it can present with minimal extrapulmonary manifestations and must be systematically excluded 1, 2, 4

Do not initiate treatment before establishing a specific diagnosis, as different interstitial lung diseases require different therapeutic approaches 4

Do not miss hypersensitivity pneumonitis - take detailed environmental exposure history as this treatable condition is frequently misdiagnosed as IPF 2