Retronasal olfactory testing using candies sent by post and for screening purposes: a feasibility study

The olfactory system is able to detect external odours through the orthonasal- and internal odours through the retronasal route. Flavour perception strongly relies on the sense of smell and this back route. In contrast to orthonasal, retronasal olfactory tests (ROT) are less frequently applied, although testing should be recommended for several reasons. The aim of the present investigation was to propose a suitable form of ROT for home-testing (and postal distribution) and evaluate a retronasal screening test.

Initially, 111 participants were tested using a 27-item version of the Candy Smell Test (CST). Fifty-four participants performed retesting, of which 25 subjects did so in a home-setting being supplied with professionally packed "candy-chains". Seven candies were chosen by means of hit rate differences in normosmics and severely hyposmics/anosmics. The 7-CST is designed in a non-forced-choice fashion with same seven flavours to choose from.

For the 27-item CST both groups (subjects performing home-testing and those performing retesting at the clinic) showed highly significant test-rest-reliabilities. The 7-CST was capable of discriminating healthy from diseased subjects when being tested in 116 healthy subjects and 47 patients suffering from olfactory dysfunction.

The CST is suitable for home-testing and postal distribution. The new 7-item CST can be valuable for rapidly revealing anosmics. These findings help in further standardizing ROT, may encourage rhinologists to more routinely evaluate retronasal olfactory abilities and pave the way for larger epidemiologic studies also in regard to food preferences and nutritional behaviour.