Setting
The Indonesian Family Life Survey (IFLS) is longitudinal large-scale survey based on samples of households living in 13 provinces from three different islands in Indonesia which represented 83% of Indonesian population.24 There are 4 provinces from Sumatra Island (North Sumatra, West Sumatra, South Sumatra, and Lampung) and 5 provinces from Java Island (DKI Jakarta, West Java, Central Java, DI Yogyakarta, East Java). Furthermore, the provinces also included Bali, West Nusa Tenggara, South Kalimantan, and South Sulawesi. The other 14 provinces were excluded due to cost-effectiveness reasons. IFLS is currently the only multipurpose population-based survey with large sample size in Indonesia that measured health outcomes.
In IFLS, a multistage stratified sampling design was used, where initially, the sampling was stratified on provinces.24 Subsequently, the sampling was conducted randomly within the provinces.
According to IFLS documentation, currently, there are a total of five waves of IFLS conducted, as follows24:
- The first wave (IFLS1) in 1993;
- The second wave (IFLS2) in 1997;
- The third wave (IFLS3) in 2000;
- The fourth wave (IFLS4) in late 2007 and early 2008;
- The fifth wave (IFLS5) in late 2014 and early 2015.
Statement of Ethics
The procedures of IFLS surveys were reviewed and approved by institutional review boards (IRBs) in both United States and Indonesia.24 In United States, the IRBs responsible for ethical review of IFLS was Research and Development (RAND) corporation, a nonprofit think tank. Meanwhile, in Indonesia, the IFLS-5 study was approved by IRBs at Universitas Gadjah Mada (UGM).
The protocol approval number given by RAND’s Human Subjects Protection Committee (RAND’s IRB) for IFLS-5 was s0064-06-01-CR01.
Funding
The funding for IFLS5 was provided by several institutions.24 Those institutions are:
- National Institute on Aging (NIA), grant 2R01 AG026676-05
- National Institute for Child Health and Human Development (NICHD), grant 2R01 HD050764-05A1
- Department of Foreign Affairs and Trade (DFAT), Government of Australia
- Grants from the World Bank, Indonesia, and GRM International
Data Availability
The datasets supporting the conclusions of this article are available from RAND website: https://www.rand.org/well-being/social-and-behavioral-policy/data/FLS/IFLS.html.
Study Design
This study was a multicenter, non-interventional, cross-sectional study using data from IFLS5 that was conducted in late 2014 and early 2015 at 13 provinces in Indonesia. Despite IFLS consisted of five waves, only the most recent wave, the fifth IFLS (IFLS5) was used for this study.
The dependent variable for this study was handgrip strength. The independent variables were hemoglobin level, gender, age, body mass index (BMI), waist circumference, smoking history, comorbidities, and current use of drug therapies.
The inclusion criteria used in this study was respondents aged ≥60 years old as in Indonesia, the elderly is defined by age 60 years and above.25 Exclusion criteria were: (1) respondents who refused to take health measurements (hemoglobin level, handgrip strength, weight, stature, and waist circumference); (2) respondents with incomplete or missing data; (3) respondents with history of stroke; and (4) respondents with a history of pain, swelling, inflammation, injury, and surgery on one or both hands within the last 6 months.
Variable Classifications and Measurements
Hemoglobin Level
Hemoglobin test was performed using capillary blood drawn from a finger prick. The measurement was performed using a Hemocue handheld meter (model Hb201+) together with its respective HB201 microcuvettes. The finger sticks lancets manufactured by Hospital and Home Care were used. Meanwhile, the dried blood spot cards used were Whatman® 903 Protein Saver Cards containing five half-inch circles with each circle capable of holding 75 to 80 μL of sample.26
Based on WHO standard, male and female participants with Hb less than 13 g/dL and 12 g/dL, respectively, were defined as anemic.27
Handgrip Strength
Handgrip strength on each hand was measured twice using a Baseline Smedley Spring type dynamometer. The dynamometer was calibrated daily.
Trained personals instructed the study participants to hold and squeeze the handle of the dynamometer as firmly as they could. The measurement begins with the dominant hand and continues with alternating hand, with a resting period in between measurements.
The value for handgrip strength used for this study was the average of both left and right hands, each measured twice. Subjects were classified as weak if the handgrip strength <28 kg for men and <18 kg for women based on classification from Asian Working Group for Sarcopenia (AWGS) 2019.19
Confounders
Confounders included in this study were age, sex, BMI, waist circumference, history of smoking, comorbidities, history of taking anemia medicine, history of taking hypertension medicine, history of taking diabetes medicine, and history of taking cholesterol medicine.
The stature of subjects was recorded to the nearest millimeter using a Seca plastic height board (model 213). Meanwhile, weights of subjects were measured using Camry model EB1003 scale to the nearest tenth of a kilogram. Subsequently, body mass index (BMI) was calculated as weight in kg divided by stature in meter square. The BMI was classified based on Western Pacific Region of World Health Organization criteria which are: (1) <18.5 kg/m2 as underweight; (2) 18.5 to 22.9 kg/m2 as normal weight; (3) 23.0 to 24.9 kg/m2 as overweight; and (4) ≥25 kg/m2 as obese.28
Waist circumference was based on cut-offs of ≥80 cm for women and ≥90 cm for men.
The comorbidities were heart disease, diabetes, hypercholesterolemia, hypertension, kidney disease, and tuberculosis. Comorbidities were assessed using the question “Have a doctor/paramedic/nurse/midwife ever told you had…. (Comorbidities mention above)”.
This study also investigated whether the participant had been taking drug therapies for anemia, hypertension, diabetes, and hypercholesterolemia. Participants were categorized into yes and no groups based on whether they take the medicine or not.
Statistical Analysis
All statistical analyses were performed using SPSS Statistical software version 21.0 (IBM Corp, Armonk, NY, USA) with statistical significance defined as p < 0.05.
In this study, categorical variables reported as percentages were used for characteristics of our study population. Prevalence of anemia and weak handgrip strength were calculated as percentages. Sex-specific and age-specific anemia prevalence were also calculated. Differences in prevalence of anemia between participants aged ≥80 years old with those aged <80 years old were assessed using Chi-square (χ2) test.
Correlation analysis was conducted using Pearson’s correlation test for data with normal distribution. If the data has non-parametric distribution, Spearman correlation was used instead. Normality of data was assessed using Kolmogorov–Smirnov test and Shapiro-Wilk test.
Logistic regression was conducted for bivariable and multivariable analysis of risk factors associated with weak handgrip strength. Subsequently, Hosmer and Lemeshow test was used to determine goodness of fit for the multivariable model. Multicollinearity test was also conducted with multicollinearity defined as variable inflation factor (VIF) >5. The multivariable analysis in this study employed a backward elimination model-building process.
Subgroup analysis was then conducted to explore the association between anemia and weak handgrip strength based on gender and age (60-69 years, 70-79 years, and ≥ 80 years)