Which variables matter in smell tests in the clinic?

Testing of olfactory thresholds in the clinic is becoming more common, with commercially produced tests now available. The effect of common potential variables in the clinic setting on these results is unclear. If many variables must be controlled, tests become more complex and a universally accepted olfactory test becomes less likely.

The aim of this study was to determine which potential variables the clinician needs to consider when testing olfaction in the out-patient clinic.

The study was conducted in a clinic setting at a university hospital, using 103 normal volunteers, comprising staff members and patients and relatives from the ENT clinic waiting room. The subjects recruited had no active rhinological complaints, were not taking any medications and were aged between 16 and 70 years. An olfactory threshold was established for each subject for the odour eucalyptol. Gender, smoking status, age, peak nasal inspiratory flow, ambient temperature and relative humidity were all recorded.

For eucalyptol, the distribution of values for olfactory thresholds in the normal population lies around the concentration 10(-3) log vol/vol. There was no significant effect of smoking status, tester, ambient temperature or humidity on the thresholds obtained.

The above variables do not have a significant effect on olfactory thresholds elicited in the clinic. The clinician therefore need not attempt to control these factors when testing olfaction in the out-patient setting. These findings bring the implementation of a universal, reliable and easily administered measurement of olfaction a step closer.