<prompt> In a Patient with clinical signs of Asthma which of the following tests will confirm the diagnosis:Increase in FEV1FVC200 ml increase in FEVI after MethacholineDiurnal variation in PEF 20 PercentReduction of FEV I 20 after bronchodilators  <response>: Answer is C Diurnal variation in PEF 20 Percent: Demonstrate Outflow Obstruction Decreased FEV1 Decreased PEF Decreased FEV1 FVC While respiratory symptoms suggest asthma, the sine qua non for the diagnosis of asthma is the presence of Reversible Airflow Obstruction andor Airway Hyper-responsiveness or Increased Peak Expiratory Flow PEF Variability in subjects without airways obstruction. Reversible Airflow Obstruction Reversibility is demonstrated by repeating spirometry results 15 minutes after administering a sho acting bronchodilator 12 reversibility in FEV1 200 ml increase in Baseline FEV1 Positive Reversibility Results Strongly Considered Diagnostic Increased Peak Expiratory Flow Rate PEF Variability Demonstration of Diurnal Variation in the Peak Expiratory Flow Rate A diurnal variation in PEF of more than 20 percent Strongly suggests a diagnosis of Asthma Considered Diagnostic Airway Hyper-responsiveness Measured by Methacholine orHistamine challenge. Increasing Concentrations of Methacholine are administered and if the FEV1 drops to 20 percent of baseline with any standard dose the test is consideredpositive. Positive test strongly suggests a diagnosis of Asthma 