Lung Function Tests vs Imaging: When You Need Which

A doctor evaluating breathing symptoms reaches for either lung function tests or lung imaging — sometimes both, often one before the other. The two answer fundamentally different questions. Lung function tests measure how the lungs work; imaging shows how the lungs look. Asthma is a function problem with often-normal imaging. Lung cancer is a structural problem that doesn't necessarily reduce function until late. Each test has its sweet spots and its blind spots.

This article clarifies when to ask for which.

Two Categories: Function vs Structure

Function tests measure physiology:

• How much air can you move?
• How fast can you exhale?
• How well do oxygen and carbon dioxide cross from air into blood?
• How much lung volume do you have?

Imaging shows anatomy:

• Are there nodules, masses, or other structural abnormalities?
• Is the airway structure normal?
• Are there signs of emphysema, fibrosis, infection, fluid?

A person with severe asthma may have completely normal chest X-ray and CT. A person with a 1 cm lung nodule may have completely normal function tests. The two complement rather than substitute for each other.

Spirometry: FEV1, FVC, FEV1/FVC Ratio

Spirometry is the most common pulmonary function test (PFT). It measures airflow and lung volumes:

• FEV1 (Forced Expiratory Volume in 1 second): how much air you can exhale in the first second
• FVC (Forced Vital Capacity): total exhaled volume after maximal effort
• FEV1/FVC ratio: percentage of total volume exhaled in 1 second

Normal FEV1/FVC: >70% (adjusted for age, sex, height, race).

Patterns:

Pattern	FEV1/FVC	FEV1	FVC	Suggests
Obstructive	<70%	Reduced	Normal or reduced	Asthma, COPD, bronchiectasis
Restrictive	>70%	Reduced	Reduced	Pulmonary fibrosis, neuromuscular, scoliosis, obesity
Normal	>70%	Normal	Normal	Healthy lungs
Mixed	<70%	Reduced	Reduced	Combined obstructive and restrictive

Reversibility test: after bronchodilator inhalation, an obstructive pattern that improves by ≥12% and ≥200 mL FEV1 suggests asthma. Persistent obstruction without reversibility suggests COPD.

Cost: $80–250 US; ¥150–350 China.

DLCO: Diffusion Capacity Tests

DLCO (diffusing capacity for carbon monoxide) measures how efficiently gas crosses the alveolar-capillary membrane. Reduced DLCO suggests:

• Emphysema (loss of alveolar surface area)
• Pulmonary fibrosis (thickened diffusion barrier)
• Pulmonary vascular disease (reduced capillary blood)
• Anemia (less hemoglobin to bind CO)
• Pulmonary embolism (reduced perfusion)

DLCO with normal spirometry: suggests early interstitial disease or pulmonary vascular disease.
DLCO with obstruction: differentiates COPD (DLCO reduced) from asthma (DLCO normal).

Cost: typically bundled with PFT panel, adds $50–150 US, ¥100–250 China.

Lung Volumes: TLC and RV

Full pulmonary function testing including body plethysmography measures:

• Total Lung Capacity (TLC): total volume after maximal inhalation
• Residual Volume (RV): volume remaining after maximal exhalation
• Functional Residual Capacity (FRC): volume at the end of normal exhalation

Hyperinflation: elevated TLC, elevated RV — characteristic of severe COPD or emphysema.
Restriction: reduced TLC — characteristic of fibrosis or chest wall problems.

Full PFT cost: $200–500 US; ¥350–700 China.

Imaging (X-Ray, CT, HRCT) Strengths

Chest X-ray: structural overview
- Visible: large masses, pleural effusion, pneumothorax, large pulmonary edema, large infections
- Misses: ~30% of early lung cancer, small nodules, early interstitial disease, mild emphysema

Standard chest CT (with or without contrast): detailed structural imaging
- Visible: nodules ≥4 mm, lymph nodes, vascular structures, mediastinal masses, pleural effusion, pneumothorax
- Sensitivity for lung cancer: ~95% at routine thickness

High-Resolution CT (HRCT): thin-section CT optimized for parenchymal detail
- Visible: interstitial patterns (ground-glass, reticulation, honeycombing, traction bronchiectasis), small airways disease, emphysema distribution
- Standard for evaluating interstitial lung disease (idiopathic pulmonary fibrosis, hypersensitivity pneumonitis, sarcoidosis)
- Cost: $700–1,500 US; ¥900–1,800 China

Low-Dose CT (LDCT): lung cancer screening
- Already discussed; for screening high-risk smokers

For interpretation of unusual imaging or function patterns, our team can help.

Bronchoscopy: When It's Added

Bronchoscopy combines visualization with tissue sampling:

• Direct visualization of central airways down to subsegmental bronchi
• Biopsy of endobronchial lesions
• Bronchoalveolar lavage (BAL) for infection or interstitial disease workup
• Transbronchial lung biopsy for peripheral disease
• EBUS for mediastinal node sampling

Ordered for:
- Persistent unexplained hemoptysis
- Suspected airway tumors
- Evaluation of unclear opacities seen on imaging
- Suspected sarcoidosis (with biopsy)
- Suspected interstitial lung disease (with biopsy and BAL)

Cost: $3,000–6,000 US; ¥4,000–8,000 China.

Combining Function and Structure

The integrated approach for breathing symptoms:

1. Chest X-ray + spirometry as initial workup
2. If function abnormal but X-ray normal: full PFT + chest HRCT
3. If imaging shows nodule or mass: spirometry as baseline for surgical planning
4. If interstitial disease suspected: HRCT + full PFT including DLCO
5. If asthma or COPD diagnosed: function-based monitoring; imaging only if symptoms change

Each test has a sweet spot — pairing tests strategically is more useful than ordering everything at once.

Comprehensive Lung Health Package in China

Top Chinese hospitals offer comprehensive lung health bundles for international patients:

Basic respiratory bundle (~¥2,500–4,000 / $350–570):
- Chest X-ray (PA + lateral)
- Spirometry with bronchodilator
- Pulse oximetry
- Basic labs

Comprehensive lung bundle (~¥4,500–7,500 / $640–1,070):
- Above plus:
- Full PFT with DLCO
- Chest CT (low-dose for screening, contrast for diagnostic)
- Pulmonologist consultation

Diagnostic lung bundle (~¥7,500–12,500 / $1,070–1,790):
- All of the above plus:
- HRCT chest
- Bronchoscopy with biopsy (if indicated)
- Cardiac assessment (ECG, echo)

Centers commonly used: Shanghai Pulmonary Hospital, PUMC Beijing, Sun Yat-sen, HKU-Shenzhen, Fudan University-affiliated hospitals.

Frequently Asked Questions

My CT was normal but I still can't breathe well. What now?
Normal CT doesn't rule out functional disease. Full pulmonary function testing (spirometry + DLCO + lung volumes) often clarifies asthma, COPD, or early interstitial disease.

Do I need both PFT and chest CT?
Often, yes. They answer different questions. For suspected lung cancer or other structural issues, CT first. For breathing problems with normal X-ray, PFT first.

What is "post-bronchodilator" testing?
The standard spirometry test is performed twice: at baseline and 15–20 minutes after inhaling a short-acting bronchodilator (e.g., albuterol). Improvement of ≥12% FEV1 suggests reversible airway disease (asthma).

Can PFT be performed in pregnancy?
Yes, safely. Spirometry doesn't involve radiation. DLCO involves brief inhalation of low-concentration CO (no fetal effect).

My DLCO is low but everything else is normal. What does that mean?
Isolated reduced DLCO can be early interstitial disease, pulmonary vascular disease, mild anemia, or early emphysema. HRCT often clarifies the cause.

Is the lung function test painful or difficult?
No. It requires forceful blowing into a tube, which can leave patients winded for a few minutes. No needles, no radiation. Most patients find the test less uncomfortable than blood draws.

Need Help Booking?

SinoCareLink can pre-book a comprehensive lung health bundle (PFT + imaging + specialist consultation) at a top Chinese hospital, translate reports into English, and arrange airport pickup. Contact us for a free consultation.