Understanding "Spirometry Results Within Normal Limits"
The automatic interpretation "Spirometry results are within normal limits" means that the measured FEV₁, FVC, and FEV₁/FVC ratio all fall above the lower limit of normal (5th percentile) when compared to reference values matched for age, height, sex, and ethnicity. 1, 2
What the Interpretation Evaluates
The spirometry system compares your measured values against predicted reference equations to determine normality:
FEV₁ (Forced Expiratory Volume in 1 second): The volume of air forcefully exhaled in the first second—your value of 2.88 L represents 91% of predicted (2.01 L predicted), which is above the lower limit of normal 3, 4
FVC (Forced Vital Capacity): The total volume of air exhaled during a maximal forced breath—your value of 3.94 L represents 134% of predicted (2.94 L predicted), which is well above normal 4
FEV₁/FVC ratio: The proportion of total lung capacity exhaled in the first second—your ratio of 74.87% exceeds the lower limit of normal and rules out airway obstruction 4, 5
How "Normal" is Defined
The lower limit of normal is statistically defined as the 5th percentile of values from healthy, non-smoking individuals matched for your demographic characteristics 2, 6
Values above this threshold are considered within normal limits, even if they don't reach 100% of the predicted value 2, 5
Your results show no evidence of obstructive defect (which would show FEV₁/FVC below the lower limit) or restrictive pattern (which would show low FVC) 4, 5
Quality Indicators in Your Report
Your test met technical quality standards:
Repeatability: Trial 1 and Trial 2 values were sufficiently close (within 0.150 L for both FEV₁ and FVC), confirming reliable measurements 1, 4
Acceptable maneuvers: The curves were free from artifacts like coughing, early termination, or submaximal effort 3, 4
Adequate exhalation time: The flow-volume and volume-time curves show complete exhalation with proper plateau formation 4
Clinical Significance
Normal spirometry effectively rules out significant obstructive lung disease (such as asthma or COPD) and does not suggest restrictive lung disease at this time 5, 6
The slightly elevated FVC (134% predicted) is not concerning and may reflect above-average lung size for your body habitus 6
Normal results do not exclude all respiratory conditions—some diseases (like early interstitial lung disease or pulmonary vascular disease) may not affect spirometry 6, 5
Important Caveats
Spirometry interpretation assumes the reference equations used are appropriate for your ethnic background; mismatched equations can lead to erroneous conclusions 6
If you have respiratory symptoms despite normal spirometry, additional testing (such as bronchoprovocation, lung volumes, or diffusing capacity) may be warranted 5, 4
The Z-scores in your report (ranging from -0.3 to 1.4 for the main parameters) confirm values are within the expected statistical range for the reference population 2