**Core Concept**
Spirometry is a pulmonary function test used to assess lung function by measuring the volume and/or flow of air in and out of the lungs. It provides valuable information about lung volumes, capacities, and airflow rates. Spirometers are essential tools in diagnosing and managing respiratory diseases.

**Why the Correct Answer is Right**
Spirometry can measure lung volumes and capacities, but it cannot directly estimate total lung capacity (TLC) because TLC includes the residual volume, which is the volume of air remaining in the lungs after a maximal exhalation. Spirometers can only measure the volume of air exhaled from the lungs, not the volume of air retained in the lungs. TLC requires additional tests, such as body plethysmography or helium dilution, to accurately estimate residual volume.

**Why Each Wrong Option is Incorrect**
**Option B:** Forced expiratory volume in 1 second (FEV1) is a critical parameter measured by spirometry, which indicates the amount of air that can be forcibly exhaled in one second. Spirometers accurately measure FEV1.
**Option C:** Peak expiratory flow (PEF) is another parameter that can be measured by spirometry, which represents the highest rate of airflow achieved during a forced exhalation. Spirometers can accurately measure PEF.
**Option D:** Vital capacity (VC) is the maximum amount of air that can be exhaled from the lungs after a maximal inhalation, and spirometry can accurately estimate VC.

**Clinical Pearl / High-Yield Fact**
When interpreting spirometry results, it's essential to remember that a reduction in FEV1/FVC ratio (forced vital capacity) is indicative of obstructive lung disease, whereas a reduction in FVC is more suggestive of restrictive lung disease.

✓ Correct Answer: A. Total lung capacity