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M.R.B. Piodena-Aportadera1, S. Lau1,2, C.N. Tan2, J. Chew1,2, J.P. Lim1, N.H. Ismail2,3, Y.Y. Ding1,2, W.S. Lim1,2


1. Department of Geriatric Medicine,Tan Tock Seng Hospital, Singapore; 2. Institute of Geriatrics and Active Aging, Tan Tock Seng Hospital, Singapore; 3. Department of Continuing and Community Care, Tan Tock Seng Hospital, Singapore

Corresponding Author: Wee Shiong Lim, Institute of Geriatrics and Active Aging, Tan Tock Seng Hospital, 11 Jalan Tan Tock Seng, Singapore 308433, wee_shiong_lim@ttsh.com.sg

J Frailty Aging 2024;13(2)98-107
Published online March 11, 2024, http://dx.doi.org/10.14283/jfa.2024.25



BACKGROUND: Screening tools such as calf circumference (CC) and Yubi-wakka (finger-ring) test have been recognized as effective tools by Asian Working Group for Sarcopenia 2019 (AWGS’19) for sarcopenia screening but their comparative agreement, diagnostic performance and validity are unclear.
OBJECTIVES: This study aims to determine: (i)agreement between calf and finger-ring circumference, (ii)diagnostic performance for low muscle mass and AWGS’19 sarcopenia diagnosis, (iii)correlation with muscle mass, strength, and physical performance, and (iv)association with frailty, life space mobility and physical activity.
METHODS: We studied 187 healthy community-dwelling older adults (mean age=66.8+7.0years) from the GERILABS-2 study. CC was measured via (i) both calves in sitting and standing positions, and (ii) Yubi-wakka test by encircling the thickest part of the non-dominant calf with index fingers and thumbs of both hands. We performed Cohen’s kappa to check for agreement, area under receiver operating characteristic curve (AUC) to compare diagnostic performance, partial correlations adjusted for age and gender to compare convergent validity, and logistic regression to determine predictive validity for outcome measures.
RESULTS: Sarcopenia prevalence was 24.0% (AWGS’19). Yubi-wakka identified 16.6% of participants as screen-positive (“smaller”), showing moderate agreement only with non-dominant sitting CC measurements (k=0.421,p<0.001) and having lower diagnostic performance in determining low muscle mass (AUC=0.591 vs 0.855-0.870,p<0.001; sensitivity=57.1% vs 75.5-90.8%; specificity=58.4% vs 70.8-80.9%) and sarcopenia diagnosis (AUC=0.581 vs 0.788-0.818,p<0.001; sensitivity=55.6% vs 57.5-71.8%; specificity=74.4% vs 75.6-88.9%) compared to CC measurements. Yubi-wakka correlated significantly with muscle mass, grip strength and knee extension but not physical performance. When adjusted for age, gender and hypertension, Yubi-wakka was significantly associated with frailty (OR=3.96,95%CI:1.09-14.38), life space mobility (OR=2.38,95%CI:1.08-5.24) and physical activity (OR=2.50,95%CI:1.07-5.86).
DISCUSSION AND CONCLUSIONS: Yubi-wakka provides a self-administered, low-cost and practicable community screening tool for sarcopenia. Our study affirmed the convergent and predictive validity of Yubi-wakka, albeit with lower sensitivity and specificity in diagnostic performance compared to CC measurements.

Key words: Sarcopenia, screening, calf circumference, Yubi-wakka.



With the considerable public health burden imposed by sarcopenia (1), there is increasing interest in early detection through screening to identify at-risk individuals so that early diagnosis and intervention can ensue to help improve health outcomes. Diagnostic modalities such as dual-energy X-ray absorptiometry (DXA) and bioelectrical impedance analysis (BIA) to measure muscle mass remain costly and are not readily available in the community. Not surprisingly, the diagnostic algorithm of consensus statements such as the Asian Working Group for Sarcopenia 2019 (AWGS’19) (2) and the European Working Group on Sarcopenia in Older People 2 (EWGSOP2) (3), as well as recently released clinical practice guidelines (4), advocate the use of simple screening tests which are easy to administer, feasible, and can be readily implemented in clinical practice and community settings. Calf circumference (CC) measurement and “Yubi-wakka” (YW) or finger-ring test are recommended by AWGS’19 as effective community screening tools to detect sarcopenia in older adults (2). Studies have demonstrated their predictive validity for incident frailty and negative outcomes including physical impairment and mortality (5, 6, 7).
CC serves as a surrogate marker of muscle mass (8, 9, 10) in older adults and has good correlation with skeletal muscle mass measurements using DXA and BIA (11) . Recent evidence suggests that CC measurements may differ by laterality (dominant versus non-dominant) and position (sitting versus standing), and that the standing position has better diagnostic performance for sarcopenia screening (12). The YW test is a convenient and practical self-screening proxy to CC measurement (13). It can be performed by lay individuals on their own in the sitting position using only fingers of both hands, compared to CC measurement which requires trained personnel using a measuring tape. Several studies support YW test as a screening tool for sarcopenia. It was assessed to be a valid screening test in comparison to the actual measurement of skeletal muscle mass index (SMI) (14). The prevalence of sarcopenia assessed by YW were found to be slightly higher in both middle-aged and older adults compared to those detected using gait speed, grip strength or skeletal muscle mass (14). It can also detect sarcopenic features in the positive “smaller” calf group such as lower body mass index (BMI), creatinine, albumin and hemoglobin (15). YW test can help identify older adults who are presarcopenic, sarcopenic and at longitudinal risk of new-onset sarcopenia (13).
Table 1 summarizes existing studies of the YW test (7, 13, 14, 15, 16, 17, 18). Notably, although CC and YW are well-validated tools for sarcopenia screening in the community, there is no prior study which directly compares the two tests in order to ascertain their comparative agreement, diagnostic performance and validity. The YW test provides a self-administered, low-cost and potentially scalable alternative to CC measurement for community screening of sarcopenia. As such, it is necessary to establish the agreement between measurements of finger-ring circumference and CC in different positions in a healthy population of community-dwelling older persons. It is also important to delineate their comparative sensitivity and specificity for sarcopenia screening, and underlying psychometric properties (construct and predictive validity) amongst healthy older persons.
Therefore, in this study, the primary aim was to determine the agreement between measurements of CC and the YW finger ring test based upon different positions in healthy community-dwelling older persons. The secondary aims were to determine their diagnostic performance for low muscle mass and AWGS’19 sarcopenia diagnosis; correlation with muscle mass, muscle function and nutrition (construct validity); and association with frailty, life space mobility and physical activity (predictive validity).

Table 1. Summary of Yubi-wakka studies

ALT, Alanine transaminase; AST, aspartate aminotransferase; AUROC, Area under receiver operating curve; AWGS’19, Asian Working Group for Sarcopenia 2019; BMI, Body Mass Index; CC, calf circumference; CI, Confidence Interval; CLD, chronic liver disease; CT, computed tomography; Hb, hemoglobin, HCC, hepatocellular carcinoma; HR, Hazards ratio; L3, third lumbar vertebrae; OR, Odd’s ratio; PI, psoas index; SMI, skeletal muscle mass index; YW, Yubi-wakka



Study Population

This cross-sectional study involved 187 participants using data at the second follow-up visit from the “Longitudinal Assessment of Biomarkers for characterisation of early Sarcopenia and Osteosarcopenic Obesity in predicting frailty and functional decline in community-dwelling Asian older adults Study” (GeriLABS-2). Details of the study have been described previously (19). In brief, this is a prospective cohort study with annual follow-up of 230 healthy community-dwelling older adults aged 50-99 years who are functionally independent in both basic and instrumental activities of daily living (bADL and iADLs), cognitively intact (modified Chinese Mini-Mental State Examination [mCMMSE] score >21) (20), generally healthy and can walk independently. For the second follow-up visit (between September 1, 2020, and December 8, 2021), 193 participants returned for the full research evaluation; we excluded 4 participants who did not complete BIA evaluation for body composition, 1 who could not perform the Yubbi-wakka test due to index finger amputation and 1 with missing data. Thus, our sample comprised 187 (81.3%) participants who completed the assessments. Written informed consent was obtained from all participants and the study was approved by the Institutional Review Board of the National Healthcare Group (No. NHG DSRB 2017/00850).

Data Collection

We collected baseline demographic data (age, gender, and ethnicity), information on cardiovascular health (hypertension, hyperlipidemia, diabetes mellitus, ischemic heart disease, atrial fibrillation, stroke/transient ischemic attack, and smoking), anthropometric measurements (height, weight, calf circumference, and relative appendicular skeletal muscle mass) and finger-ring test of the participants in the study. To measure obesity, we employed body mass index (BMI) and waist circumference (WC). We used the BMI cut-off of >27.5kg/m2 to define obesity as recommended by World Health Organization for Asian Populations (21, 22), of which mortality risk is higher (23). WC cut-offs of >90cm and >80cm were used for males and females respectively according to the Asia Pacific Consensus by the International Diabetes Foundation Consensus Worldwide Definition of the Metabolic Syndrome (24, 25).
Nutritional status was assessed using the Mini-Nutritional Assessment (26) and Simplified Nutritional Appetite Questionnaire (27). Functional status was assessed using the Modified Barthel Index (MBI) (28) for bADL, and Lawton and Brody’s Index (29) for iADL. Physical activity was measured using Frenchay Activities Index (30), and International Physical Activity Questionnaire (IPAQ) (31). Life-space mobility was assessed using the Life-Space Assessment (32) which comprises five space-levels corresponding to activities outside the bedroom, home, neighbourhood, town, and beyond. Using cohort quintile cut-offs, we defined low physical activity as Frenchay Activity Index ≤29 and IPAQ <2826 METS respectively, and low life-space mobility as Life-Space Assessment <76 (33). Physical frailty was assessed using the modified Fried Frailty Phenotype criteria (34), with a score of 0 denoting non-frail, 1–2 denoting prefrail, and 3 and above denoting physical frailty.
We measured relative appendicular skeletal mass (ALM) using multi-frequency bioimpedance analysis (InBody 770; InBody, Seoul, Korea). Fat-free lean body mass in the four limbs was summed and standardized using the square of the height to obtain the relative appendicular skeletal mass. Muscle function was assessed based on muscle strength and physical performance. For muscle strength, we measured the maximum hand grip strength using a hydraulic hand dynamometer (North Coast Medical Inc., Gilroy, CA, USA) and knee extension strength using an electronic push/pull dynamometer (BASELINE 12-0342; Fabrication En- terprises Inc., White Plains, NY, USA). For physical performance, we assessed usual gait speed on a three-meter walk test and the time taken to perform five chair stands with a sitting stop. Overall physical performance was measured using Short Physical Performance Battery (SPPB) (35), a three-component test comprising balance, gait speed and repeated chair stand. Sarcopenia was defined using the AWGS’19 criteria as follows: (1) low muscle mass (<7.0 kg/m2 in male and <5.7 kg/m2 in female); along with (2) low handgrip strength (<28 kg in male and <18 kg in female) and/or slow usual gait speed (<1.0 m/s) (2).

Calf Circumference Measurement

Calf circumference was measured at the widest part of the calf using a non-elastic tape snugly applied flat on the skin and parallel to the floor with caution not to compress the calf. CC was first measured in the sitting position with the knee and ankle bent at a right angle and the feet flat on the floor. Standing CC was then measured with the feet at shoulder-width distance for equal distribution of body weight. Altogether, four readings were obtained: dominant and non-dominant sides in the sitting and standing positions. Cutoffs for low CC were <34cm in men and <33cm in women as per the AWGS’2019 recommendations (2).

Yubi-wakka Test

YW or finger-ring was performed by making a ring with the index fingers and thumbs of both hands and circling the thickest part of the non-dominant calf of the participant’s leg bent at a 90° angle, checking whether the calf is “bigger,” “just fits” or “smaller” as compared with finger-ring circumference. This was self-performed in a seated position without the use of any instrument (13). As per the recommendations, a positive YW test result is indicated by a “smaller” calf size compared to finger ring circumference (13).

Statistical Analysis

We performed statistical analyses using IBM SPSS Statistics for Windows, version 23.0 (IBM Corp., Armonk, NY, USA). Statistical tests used were two-tailed, with the level of significance set at 5% (p<0.05). Quantitative or continuous variables were expressed as mean ± standard deviation or median (interquartile range). Categorical variables were expressed as absolute and relative frequencies or counts and percentages.
We first performed Cohen’s kappa to check for agreement between screen-positive for CC measurement and YW test. To compare their diagnostic performance, we generated receiver operating characteristic (ROC) curves against the AWGS’19 criteria for sarcopenia as the reference standard. The area under the ROC curves (AUCs) were compared using the DeLong method (36). We determined the optimal cut-off value using the Youden index method and derived the corresponding sensitivity, specificity, positive predictive value, and negative predictive value. We further performed subgroup analysis for sarcopenic non-obese and sarcopenic obesity.
As a measure of construct (convergent) validity, we performed partial correlation adjusted for age and sex comparing CC and finger-ring circumference against appendicular skeletal mass, muscle strength, muscle function, and nutrition, respectively. To determine the predictive ability for outcome measures, we performed binary logistic regression adjusting for age, gender and hypertension.
We performed sample size calculation using MedCalc for Windows (version 20.018; MedCalc Software, Ostend, Belgium). The reported area under ROC for the Yubi-Wakka test ranges from 0.697 to 0.729. Assuming area under ROC of 0.697, Type 1 error (α) of 0.5, study power (1−β) of 0.80, and sarcopenia prevalence of 15%, we will require 134 participants. Thus, for our actual sample size of 187, using the same assumptions as before, this will yield a power of 91%.



Baseline Characteristics

The mean age was 66.8 ± 7.0 years with Chinese (93.6%) and female (73.3%) predominance (Table 2). Hyperlipidemia (62%), hypertension (33.2%), and diabetes mellitus (12.3%) were the most prevalent cardiovascular risk factors. The high scores for basic and instrumental ADL (mean scores of 100 and 23, respectively), Frenchay Activities Index (mean ± SD: 30.97 ± 4.6) and Mini-Nutritional Assessment (27.52 ± 1.8) attested to the relatively robust health of the study participants. The prevalence of obesity was 9.6% based on high BMI of >27.5 kg/m2 and 62.6% based on high WC criteria.
Based on CC measurements, the prevalence of positive screen for sarcopenia ranged from 32.6 to 34.2% in the standing position and 23.5 to 26.2% in the sitting position. In contrast, the prevalence of YW positive screen (smaller group) was 16.6%. Comparing between sarcopenia and non-sarcopenia groups, there was a significant difference in CC measurements and proportion of screen-positive cases for both CC and YW (all P<0.001).

Table 2. General characteristics

Presented as mean + standard deviation, median (IQR, interquartile range) or N (%); *p<0.01; ALMI, appendicular lean mass index; bADL, basic activities of daily living; BMI, Body Mass Index; FAI, Frenchay Activities Index; iADL, instrumental activities of daily living; IPAQ, International Physical Ativity Questionnaire; LSA, Life-Space Assessment; MNA, Mini-Nutritional Assessment; SNAQ, Simplified Nutritional Appetite Questionnaire; SPPB , Short Physical Performance Battery; TIA, Transient Ischemic Attack; WC, waist circumference; AWGS’19 cut-offs were used for sarcopenia diagnosis


Comparing YW with other muscle measures for sarcopenia case detection, YW has lower detection rate (16.6%) compared with gait speed (29.4%), grip strength (19.8%), and skeletal muscle mass (SMM) (47.6%).

Agreement between calf and finger-ring circumference

There is only fair to moderate agreement between screen positivity for YW test and CC (Table 3). The kappa agreement is higher in the sitting (kappa: 0.373 – 0.421) compared with standing position (kappa: 0.309 – 0.331), and also for non-dominant compared with dominant readings.

Table 3. Agreement between yubi-wakka test and calf circumference measurements

1. Yubi-Wakka (smaller) compared with AWGS’19 cutoffs for calf circumference


Diagnostic performance for low muscle mass and AWGS’19 sarcopenia diagnosis

Table 4 compares the diagnostic performance of YW test and CC for low muscle mass and AWGS’19 sarcopenia diagnosis. Compared with CC measurements, YW has lower diagnostic performance in determining low muscle mass (AUC = 0.591 vs 0.855 – 0.870, P<0.001 for comparison with YW) and sarcopenia diagnosis (AUC = 0.581 vs 0.788 – 0.818, P<0.001 for comparison with YW). This is attributable to the lower sensitivity (57.1% vs 75.5 – 90.8%), specificity (58.4% vs 70.8 – 80.9%) and positive predictive value (21.5% vs 50.2 – 65.7%) for low muscle mass and the lower sensitivity (55.6% vs 57.5 – 71.8%), specificity (74.4% vs 75.6 – 88.9%), positive predictive value (30.2% vs 47.2 – 71.5%) and negative predictive value (64.6% vs 81.2 – 89.5%) for sarcopenia diagnosis.

Table 4. Comparison between finger-ring circumference and calf circumference measurements

AUC, area under the curve; CI, confidence interval; NPV, negative predictive value; PPV, positive predictive value; SMI, skeletal muscle mass index; Sn, sensitivity; Sp, specificity; *p<0.001, compared with finger-ring


When the participants with sarcopenia were further stratified by obesity measures using WC cutoffs into sarcopenic non-obesity (SNO) and sarcopenic obesity (SO) subgroups, the corresponding AUCs were 0.607 (95%CI: 0.469 – 0.74) for SNO and 0.559 (95%CI: 0.435 – 0.682) for SO.


Correlation with muscle mass, muscle strength, physical performance and nutrition

Adjusting for age and gender, YW test result had significant albeit weak- correlations with muscle mass (r = -0.169, p<0.05), grip strength (r = 0.244, p<0.01), and knee extension (r = 0.161, p<0.05). There was no significant correlation with physical performance indices or nutritional status (Appendix Table 1). CC measurements showed good correlation with muscle mass (adjusted r, 0.653 – 0.693) and fair correlation with muscle strength (adjusted r, 0.229 – 0.381). CC measurements in the dominant position showed significant correlations with physical performance in the domains of repeated chair stand and SPPB.

Association with frailty, life space mobility and physical activity

When adjusted for age, gender and hypertension, a ‘smaller’ reading on YW test was significantly associated with low physical activity (IPAQ) (OR = 2.50, 95% CI of 1.07 – 5.86); low life space mobility (OR = 2.38, 95% CI of 1.08 – 5.24) and physical frailty (OR = 3.96, 95% CI of 1.09 – 14.38) although there was no association with the Frenchay Activities index. A similar pattern was seen for CC, with screen positive cases showing comparable odds for IPAQ (adjusted OR range, 1.88 – 2.68), higher odds for life space mobility (adjusted OR range, 2.89 – 4.09), and lower odds for physical frailty only in the standing position (adjusted OR range, 2.86 – 3.26).

Table 5. Logistic regression analysis for finger-ring and calf circumference measurements with frailty and functional ability

Model 1: unadjusted; Model 2: adjusted for age, gender and hypertension; CC, calf circumference; CI, Confidence interval; FAI, Frenchay Activities Index; FFP, Fried Frailty Phenotype; IPAQ, International Physical Activity Questionnaire; LSA, Life-Space Assessment; OR, Odds ratio; CI, Confidence interval; *p<0.01; **p<0.05



Yubi-wakka provides a self-administered, low-cost and practicable community screening tool for sarcopenia. Despite being recommended by AWGS’19 as a possible screening tool for sarcopenia (2), there is a gap in understanding the comparable agreement, diagnostic performance, and validity of the self-administered YW test versus personnel-measured CC in different positions (7, 13, 14, 15, 16, 17, 18). Our study thus bridges this evidence gap by ascertaining and directly comparing both tests in a healthy population of community-dwelling older adults. Our results demonstrate that the two tests are not inter-changeable, with only fair to moderate agreement for screen-positivity. Moreover, YW has a lower case-detection rate with poorer diagnostic performance for both low muscle mass and sarcopenia diagnosis. Nonetheless, there is evidence to support the construct validity (albeit weaker than CC) and predictive validity. Taken together, our study affirmed the validity of the YW test for community screening of healthy older persons, albeit with lower case-detection rate due to decreased sensitivity and specificity in diagnostic performance when compared to CC measurements.
Although the two tests are indicators of muscle mass using finger-ring and trained personnel tape-measurements of calf circumference respectively, their results are not inter-changeable. Firstly, we demonstrated fair agreement between YW and CC measurement in all positions, with the exception of the non-dominant calf in the sitting position where there is moderate agreement. This is not surprising, as the latter corresponds to the measurement protocol for the YW test which is performed using the non-dominant calf in a seated position. The non-dominant sitting position is the measurement protocol for detection of risk of malnutrition using the Mini-Nutritional Assessment (26) whereas AWGS’19 recommends the maximum value of both calves without specifying the measurement position (2). Notably, a recent study reported that the sitting position can systematically over-estimate CC measurements by 0.7cm compared to standing (12), which corresponds to the higher detection rate for sarcopenia in the standing compared to the sitting position in our study. Secondly, the YW test has significantly inferior diagnostic performance for low muscle mass and sarcopenia diagnosis attributed to its lower sensitivity and specificity amongst healthy older persons. Of note, the analogous CC measurement in the non-dominant sitting position has comparatively lower diagnostic performance compared with other CC measurement positions due to the lower positive predictive value.
The case detection rate for positive YW is lower compared with other sarcopenia case detection measures such as gait speed, grip strength and SMM. It has lower sensitivity compared to the previous study by Watanabe (14), in which the study population is older with a higher proportion aged >=70 years; more frail (higher proportion with slow gait speed); and may have a lower prevalence of central obesity. There may also be population differences in the finger-ring circumference which may affect case detection rate.
Similarly, our results showed generally lower sensitivity with comparable specificity with earlier studies (16). This may be due to the fact that YW may be less sensitive in healthier and more robust populations such as in our study. Furthermore, the high prevalence of central obesity (62.6% defined by high WC) may further attenuate the pick-up rate of YW. Our results indicate that YW has poorer diagnostic performance in SO compared with SNO. This is consistent with previous literature which reported the reduced diagnostic performance of calf circumference (37) in SO and may account for the lower sensitivity of Y-W for sarcopenia identification in our study.
Our results support the construct validity of YW in healthy older persons for muscle mass and strength, but not physical performance or nutrition. The significant correlation with muscle mass, grip strength and knee extension was similar to the results of an earlier study showing significant association of the YW test with body fat, appendicular skeletal muscle mass, skeletal muscle mass index, and other body composition elements (14). Another study also reported association of the ‘smaller’ group on YW test with lower weight and muscle mass as well as weaker upper and lower extremity strength, compared with the ‘bigger’ or ‘just fits’ counterparts (13). A recent study demonstrated that changes in YW test from ‘bigger’ to ‘smaller’ at one-year was associated with low or decreasing body mass index (18). Nonetheless, the YW test can only be used to evaluate calf size but not subcutaneous or intramuscular fat tissue (18) thus accounting for the lack of correlation with physical performance measures such as repeated chair stand, gait speed and SPPB. The comparatively lower correlations with muscle mass and strength vis-a-vis CC measurements suggest that the construct validity may be attenuated by other factors such as individual variations in finger-ring circumference and measurement issues.
In addition, our study corroborates the predictive validity of YW by demonstrating that the positive group (“smaller”) is significantly associated with physical frailty, life space mobility and physical activity. It has been suggested that the YW test has been adjusted for differences in body size due to differences in hand size -and hence the encircling finger-ring-, making it a custom-made indicator for individualised sarcopenia risk assessment (13). A previous study (15) found that the YW positive group tended to have lower BMI, creatinine, albumin and hemoglobin, which suggests that the test can detect sarcopenic features in the positive “smaller” calf group. Low BMI indicates low body muscle mass content while creatinine and albumin levels positively corelate with muscle mass, thus lending credence that sarcopenia is the major cause (38) and a precursor syndrome for the physical manifestation of frailty (39) in the screen-positive cases.
This study has some limitations. First, this was a cross-sectional analysis which limited the exclusion of reverse causal relationships from observed associations with outcomes. The cross-sectional design also precluded longitudinal measurements of finger-ring circumference; changes in the YW test results have been proposed as an alternative for early detection of those who are at high risk for sarcopenia (18). Second, this study comprised an Asian population of predominantly Chinese older adults. Thus, results may not be generalizable to populations of non-Chinese ethnicity who may have differences in terms of finger-ring size, prevalence of sarcopenia and preferences for self-administered screening tests for sarcopenia (15). Lastly, results from this study are only applicable to healthy, community-dwelling older adults who can measure their own calves using the YW test, and may not be generalizable to older persons who are frailer in health status.
Our study affirmed the validity of the YW test for community screening of sarcopenia in healthy older persons, albeit with lower case-detection due to decreased sensitivity and specificity in diagnostic performance when compared to CC measurements. When considering the role of YW as a community screening tool for sarcopenia, the practicality and potential scalability of self-administration without the requirement for specialized equipment or personnel would need to be balanced against the poorer diagnostic performance with consequent lower case-detection. It is plausible that the diagnostic performance may be even lower when implemented in the real-world setting. Future large-population implementation studies comparing well versus at-risk populations are therefore required to ascertain the diagnostic performance of YW in the real-world setting.


Acknowledgements: The authors would like to thank all study participants who contributed to this study. We are also grateful to Audrey Yeo, Suzanne Yew for their invaluable assistance with data collection.

Conflicts of Interest: The researchers claim no conflicts of interest.

Funding: This research was funded by the Lee Foundation Grant 2019. The funder had no role in the design of the study; in the collection, analyses, or interpretation of data; in the preparation of the manuscript, or in the review or approval of the manuscript and in the decision to publish the results.

Ethical standards: The National Healthcare Group Domain Specific Review Board (DSRB) granted ethics approval for this study (DSRB reference number: 2017/00850).





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