The demographic and clinical characteristics of the subjects are summarised in Table 1. Of the 137 subjects, 28 (20.4%) were men and 109 (79.6%) were women, with the mean age being 71.60 ± 7.56 years. The mean combined TDI score, based on the YSK olfactory function test, was 17.46 ± 5.49. The detection threshold for PEA, based on the sniffing bead system, was 2.58 ± 1.52.
Table 1
Characteristics of the enrolled subjects
Variables | Number |
Number | 137 |
Sex | |
Male: female | 28:109 |
Age (years) | |
Mean ± SD | 71.60 ± 7.56 |
Range | 58–92 |
Smoking | |
Non-smoker, n (%) | 134 (98.5%) |
Smoker, n (%) | 3 (1.5%) |
Number of subjects with AD (%) | 38 (28.1%) |
Number of subjects with VD (%) | 7 (5.2%) |
MMSE-K | 22.08 ± 6.56 |
CERAD-K | 60.05 ± 22.72 |
YSK_Threshold | 2.41 ± 1.79 |
YSK_Discrimination | 6.11 ± 2.07 . |
YSK_Identification | 8.93 ± 3.25 |
YSK_TDI | 17.46 ± 5.49 |
Threshold for PEA sniffing bead _ threshold | 2.58 ± 1.52 |
AD, Alzheimer’s disease; CERAD-K, Consortium to Establish a Registry for Alzheimer’s Disease- Korean version; MMSE-K, Mini-Mental State Examination-Korean version; PEA, 2-phenylethyl alcohol; SD, standard deviation; VD, Vascular dementia; YSK_TDI, YSK_Threshold-Discrimination-Identification |
The correlation between scores was evaluated based on the YSK olfactory function test, i.e. standard testing; the detection threshold for PEA was evaluated based on the novel sniffing bead system. The threshold and identification scores of the YSK olfactory function test were positively correlated (YSK_Threshold: p < 0.001, r = 0.4296 and YSK_Identification: p = 0.0147, r = 0.2080, respectively) with the detection threshold scores for PEA also based on the sniffing bead system. However, the discrimination component of the YSK olfactory function test was not significantly correlated (YSK_Discrimination: p = 0.1017, r = 0.1404) (Fig. 1A–C). The combined TDI score of the YSK olfactory function test was also positively correlated with the detection threshold scores for PEA based on the sniffing bead system (YSK_TDI: p < 0.001, r = 0.3164) (Fig. 1D).
Subsequently, subjects were divided into groups based on cognitive function. Eighty-four subjects were classified as having normal cognitive function and 53 were classified as having impaired cognitive function. In the normal cognitive function group, YSK_Threshold, YSK_Identification, and YSK_TDI were significantly correlated with the detection threshold scores for PEA based on the sniffing bead system. In the impaired cognitive function group, YSK_Threshold and YSK_TDI were significantly correlated with the detection threshold scores for PEA, also based on the same system. R-values, p-values, and 95% confidence intervals for all correlations are given in Table 2.
Table 2
Correlation between each component of the olfactory function test (YSK) and the 2-phenylethyl alcohol detection threshold in subjects with and without cognitive impairment
| Normal | Cognitive impairment |
| r | p | r | p |
YSK_Threshold | 0.4791 | < 0.001 | 0.3816 | 0.0057 |
YSK_Discrimination | 0.1959 | 0.0742 | 0.1746 | 0.2205 |
YSK_Identification | 0.3166 | 0.0033 | 0.2572 0.0 | 0.0684 |
YSK_TDI | 0.4294 | < 0.001 | 0.3538 | 0.0109 |
YSK_TDI, YSK_ Threshold-Discrimination-Identification |
Next, we evaluated the time required to conduct each olfactory test. The mean duration of the YSK_Threshold test was 6.41 ± 2.71 min for all subjects, with a mean test duration of 6.35 ± 2.40 min and 6.51 ± 3.17 min in subjects with normal and impaired cognitive function, respectively. The mean duration of the YSK_Discrimination test was 7.62 ± 2.23 min for all subjects, with a mean test duration of 7.5 ± 1.96 min and 7.83 ± 2.61 min in subjects with normal and impaired cognitive function, respectively. The mean duration of the YSK_Identification test was 6.43 ± 1.96 min for all subjects, with a mean test duration of 6.20 ± 1.65 and 6.79 ± 2.35 min in subjects with normal and impaired cognitive function, respectively. The mean duration of the complete YSK olfactory function test battery was 20.43 ± 5.29 min in all subjects, with a mean test duration of 20.05 ± 5.01 min and 21.01 ± 5.72 min in the those with normal and impaired cognitive function, respectively. In contrast, the mean test duration of the PEA-based sniffing bead system was 5.00 ± 1.51 min for all subjects, with a mean test duration of 4.87 ± 1.36 and 5.01 ± 1.44 min in the normal and impaired cognitive functioning groups, respectively. The mean test duration for the PEA-based sniffing bead system (5.00 ± 1.51 min) was significantly shorter than that of the YSK_Threshold (6.41 ± 2.71 min), YSK_Discrimination (7.62 ± 2.23 min), YSK_Identification (6.43 ± 1.96 min), and YSK_TDI tests (20.43 ± 5.29 min) (Fig. 2).
Finally, the generalisability of the sniffing bead system to other odours was evaluated. The detection threshold scores for PEA and n-butanol sniffing bead systems were significantly correlated (Fig. 3).