The applicability of the “Sniffin’ Sticks” olfactory test in a Turkish population

Background

The sense of smell plays important roles in daily human life, and loss of olfaction is mostly expressed in terms of a severe decrease in quality of life. Problems in quality of life were reported primarily in the areas of eating and safety [1–4]. The major causes of olfactory disorders are head injury, infections of upper respiratory tract, sinonasal diseases, head trauma, and toxic exposure.

Approximately 5% of the general population is anosmic (no sense of smell), but about 15% have reduced olfactory function [5–8]. A significant number of patients complain of a reduction in their olfactory function, so it becomes important to use appropriate diagnostic tools (e.g., the University of Pennsylvania UPSIT Smell Identification Test [9], “Sniffin’ Sticks” [10,11], or measurements of event-related potentials [12]). Quantitative smell disorders such as anosmia or hyposmia can be differentiated from normal olfactory function.

The “Sniffin’ Sticks” test was initially developed and validated on large numbers of patients in Germany [10,13]. Currently, the kit is used by many clinicians around the world and has been validated in various countries and populations (e.g., Australia [14], Greece [15,16], Taiwan [17–19], Italy [20], Holland [21], Sri Lanka [22], and Brazil [23]). The “Sniffin’ Sticks” test has been validated and normative data published on a large number of subjects in Northern Europe and smaller studies have proven its usefulness in assessing olfaction in populations around the world, but there is only 1 study evaluating the “Sniffin’ Sticks” olfactory test in Turkey [24]. In that study researchers found quite poor scores in a Turkish population when compared to other worldwide studies. Thus, we aimed to re-investigate the normative data for “Sniffin’ Sticks” olfactory test in healthy Turkish subjects. Another goal of this study was to compare the scores of subjects with and without a complaint of olfactory dysfunction for detecting the clinical applicability of the “Sniffin’ Sticks” olfactory test.

Material and Methods

STATISTICAL ANALYSIS:

Data analysis was performed by SPSS 21.0 (Statistical Package for Social Sciences, SPSS Inc. Chicago, IL). The normal distribution of considered variables was evaluated using the Shapiro-Wilk test. Data are shown as mean ?standard deviation for continuous variables and number of cases was used for categorical variables. Demographic data of the subjects were compared by t test or chi-squared test, as appropriate. To explore general olfactory sensitivity (TDI score) in relation to age and sex, data were submitted to analysis of variance (ANOVA) using the general linear model with between subject factors? age group? and sex?with Bonferroni post hoc tests. The level of significance was set at 0.05.

Results

The study was carried out in 174 subjects between the ages of 18–68 years. The participants were divided into 2 groups according to subjective olfactory function, either healthy or abnormal. Most participants (68%) had a high educational level (high school or university) and there was no difference between the groups in terms of education and age; however, there was significant difference in terms of sex.

Table 1 summarizes the characteristics of each of the variables of interest by disease status. Differences in TDI, T, D, and I were significant between the abnormal and healthy groups.

Descriptive statistics of normative values obtained in healthy subjects are shown in Table 2. When all the age groups were considered together in healthy subjects, the 10th percentiles of odor threshold score, odor discrimination score, odor identification score, and TDI score were 7.25, 12, 11, and 32, respectively.

ANOVA testing did not reveal a significant effect of age on T, D, or TDI scores but a significant decrease was detected in I scores in subjects over the age of 55 (p=0.04).

A significant effect of subject sex was found in the I score (p=0.03) and TDI score (p=0.02), with females being more sensitive than males.

In the healthy group, some odorants were consistently correctly identified but others were not. Peppermint, rose, fish, banana, cloves, garlic, and coffee were the odorants most reliably identified correctly, while turpentine, apple, leather, lemon, and liquorice were most commonly mistaken (Figure 1). In the abnormal group, as expected, a larger proportion of subjects wrongly identified odorants (Figure 2). Considering the 2 groups together, apple and turpentine were the least well-recognized odors from the 16 presented.

Discussion

Our study provides an update of normative values for routine clinical use of “Sniffin’ Sticks” in Turkish populations. Also, the present study validated that the “Sniffin’ Sticks” olfactory test is suitable for clinical usage in Turkish populations.

“Sniffin’ Sticks” is a modern olfactory test recommended by the German Olfactology and Gustology Association as a standard for olfactory testing [7]. However, cultural differences make the application of the odor identification tests in different countries difficult, because odor identification is strongly dependent on familiarity with the odors tested. When applied cross-culturally, the “Sniffin’ Sticks” test appears to perform well, but in some populations the test required adaptation using different distracters in the 4 alternative forced multiple-choice identification subtest [16–19].

In a validating study conducted in Taiwan, although the odorants were kept the same, some descriptors were changed from the original version. The authors concluded that the “Sniffin’ Sticks” test appears to be suited for the assessment of olfactory identification in an Asian population after revision of the descriptors [18,19].

Two studies were conducted in Greece on healthy subjects. In 1 of the studies the authors did not encounter any problematic items in the identification list and found the “Sniffin’ Sticks” test well-adapted to testing olfaction in a Greek population [15]. The other, larger, study showed decreased identification (<70%) for 6 of the odorants: aniseed, turpentine, liquorice, apple, lemon, and cinnamon [16]. The modifications in the list of descriptors after linguistic changes significantly increased the identification of problematic items. Translation and cultural adaptation of the descriptor list in the identification subtest was used in studies conducted in Brazil, Sri-Lanka, and the Netherlands, with the test being validated against normative data from Germany [21–23].

In a randomized crossover study on patients with hyposmia and anosmia, the investigators modified the distracters, using more contrasted distracters (contrasted test) [27]. Patients with hyposmia performed better in the contrasted test in odor identification, but patients with anosmia did not. It appears that the use of more contrasted distracters can contribute to better discrimination between patients with hyposmia and anosmia, which is important in a clinical context.

In our Turkish population, the odors most commonly mistaken in the healthy group were turpentine (54%), apple (25%), lemon (21%), liquorice (21%), and pineapple (17%). In the abnormal group, the most commonly mistaken odorants were apple (72%), cinnamon (67%), turpentine (63%), pineapple (55%) and liquorice (55%). A possible explanation for these results could be the similarity of distracters with the odorant, as in the case of apple (distracters are orange, peach, and melon), cinnamon (distracters are honey, vanilla, and chocolate) and lemon (distracters are grapefruit, apple, and peach) or unfamiliarity with an odorant such as turpentine, liquorice, and pineapple. Another possible reason for the difficulties in identification could lie in the odor itself: the currently used apple odor smells like Granny Smith apple and the participants confused this odor with air freshener. In Turkish culture, people are accustomed to more sugary and sweet apple types. Also, some of the odors presented as distracters may not be very familiar to Turkish populations, for example ham, wine, rum, or gummy bears.

According to Hummel et al., a criterion for the selection of odorants was the successful identification of individual odorants from a list of 4 descriptors should be >75% in healthy subjects [28]. Based on this view, we propose replacing turpentine with an odorant more familiar to Turkish culture. Our study had a limitation due to the low number of participants over the age 55. Thus, further studies with a higher number of participants including all age groups are needed for the Turkish population.

Conclusions

These results provide the basis for routine clinical evaluation of patients with olfactory disorders using the “Sniffin’ Sticks” test in Turkish populations.