Correlation between Skinfold Thickness and Total Daily Dose of Insulin in Patients with Type 2 Diabetes Mellitus in a Tertiary Hospital

Introduction: Type 2 diabetes mellitus (T2DM) is a non-communicable disease with a high prevalence in Indonesia. T2DM is caused by insulin resistance and relative insulin deficiency. One of the therapy for T2DM is insulin administration which is injected into the subcutaneous tissue. The absorption of insulin in the subcutaneous tissue is influenced by many factors, one of which is the thickness of subcutaneous fat. This study aimed to determine the correlation between the skinfold thickness of T2DM patients with the total daily dose of insulin needed every day. Methods: This was an observational analytic study using a cross-sectional design to analyze the correlation between subcutaneous fat thickness represented by skinfold thickness and the total daily dose of insulin of T2DM patients. Measurement of skinfold thickness was carried out on the triceps using a skinfold caliper. Data on the patient's total daily dose of insulin were obtained from medical records. Results: A total of 53 patients were included in this study. The patient's mean triceps skinfold thickness was 26.29±8.72 mm. The mean total daily dose of insulin was 40.96±18.01 IU. The results of the Spearman Rank correlation test showed a significant correlation between skinfold thickness on the triceps and the patient's total daily dose of insulin (p<0.05). Conclusion: The higher the skinfold thickness, the greater the dose of insulin needed by the patient.


INTRODUCTION
Diabetes mellitus has several different types, one of them is the type 2 diabetes mellitus (T2DM).Patients with T2DM suffer from insulin resistance and relative insulin deficiency (ADA, 2010).Type 2 diabetes mellitus (T2DM) is a noncommunicable disease with a high prevalence in both the world and Indonesia.Based on International Diabetes Federation (IDF), Indonesia ranks 7th as the country with the highest diabetes prevalence in the world, which affects 10.7 million people, and predicted to raise to 16.6 million in 2045 (IDF, 2019).
The pharmacological therapy for controlling T2DM can be in the form of oral on injected medications.One of the types of injected medication is insulin.Insulin for T2DM is considered to be given if the glycaemic target (A1C <7%) is not achieved after the patient has received monotherapy or dual therapy for 3 months (ADA, 2019).The American Association of Clinical Endocrinologists (AACE) recommends initiation of long-acting basal insulin with a total daily dose (TDD) of 0.1 -0.2 unit/kg for patients with A1C <8% or 0.2 -0.3 unit/kg for patients with A1C > 8%, with titration every 2 -3 days to achieve the glycaemic target.Initiation and titration of insulin in T2DM patients can be a challenge for primary healthcare providers resulting in delayed in insulin initiation (Chun et al., 2019).This delay significantly impacts the increased risk of developing microvascular complications of diabetes mellitus (Chun et al., 2019).
Insulin is injected into the subcutaneous tissue.The absorption rate of insulin can be varied depending on several factors, such as the fat thickness of the subcutaneous tissue where insulin is absorbed from.High subcutaneous fat may slow the absorption and change or delay the timeaction profile of insulin and people with severe obesity may need a higher insulin daily dose and multiple split insulin injections to enhance its action and predictability (Morello, 2011).Subcutaneous fat thickness can be measured indirectly by measuring the skinfold thickness (Duren et al., 2008).The triceps is the most frequently chosen site for measuring skinfold thickness because it is easily accessible, reproducible, and can measure wide differences between people (Wang et al., 2006).Triceps skinfold thickness indicates peripheral subcutaneous fat (Eaton-Evans, 2012) and also correlates with BMI (body mass index) (Chavhan et al., 2020).Differences in skinfold thickness are associated with variability of insulin depot size, subcutaneous blood flow, and insulin absorption in diabetics (Gradel et al., 2018).This study aimed to determine the correlation between the skinfold thickness of T2DM patients with the total daily dose of insulin needed every day.

METHODS
This was an analytic observational study using a crosssectional design.This study was conducted in the Endocrine outpatient clinic at Dr. Soetomo General Academic Hospital, Surabaya, Indonesia.The subjects of this research were recruited using purposive sampling method.The inclusion criteria for this research were T2DM patients who used insulin injections as their therapy, having A1C <8%, and did not get insulin dose titration.Whereas, the exclusion criteria were T2DM patients receiving additional therapy, either insulin or oral antidiabetic drugs (OAD), having a history of hospitalization in the last 3 months, and had more than 2 kg weight loss in the last 3 months.The patients who met the inclusion and exclusion criteria were then recruited as subjects for this research.All of the subjects' skinfold thickness on the triceps was measured using the Harpenden skinfold caliper two times and the average was recorded.The subjects' total daily dose of insulin and characteristics, such as age and sex, were obtained from the medical records.The correlation of skinfold thickness and the total daily dose of insulin then were analyzed using IBM SPSS Statistics ver.

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This research was approved by the Health Research Ethics Committee of Dr. Soetomo General Academic Hospital with Ethical Clearance number 0303/KEPK/XI/2021.All the subjects were given informed consent before agreeing to become the subject of this research.

RESULTS
The total number of patients who met the inclusion and exclusion criteria and were recruited from April to August 2022 was 53.The subjects' age and gender are shown in Table 1.The mean age of the subjects was 53.9±8.9 years, with the highest age group being 50-59 years and the lowest being 30-39 years.Sex distribution of the subject showed that the number of female patients was 27 people and the males was 26 people.The mean for the triceps skinfold thickness was 26.29 mm and it was higher in females than in males.For the insulin total daily dose, the mean was 40.96IU, as shown in Table 2.
The correlation between triceps skinfold thickness and the total daily dose of insulin was determined using Spearman's Rank Correlation because the data distribution was not normal.The result was p<0.05, meaning there was a significant correlation between the two variables.The coefficient correlation value was r=0.325 which showed a moderate relationship, which can be seen in Table 3.  2022) that the prevalence of T2DM in females and males is rather equal.Tramunt et al. (2020) reported that the prevalence of T2DM was higher in males because they are more likely to be obese, have insulin resistance, and have hyperglycemia than in females.
The average triceps skinfold thickness results found in this study was 26.29±8.72 mm, with females having it higher than males.A higher triceps skinfold thickness in females was also found in other studies in Turkey and India (Selcuk et al., 2013;Chavhan and Chandrachood, 2020).This is possible because total body fat in females is higher than in males and it is mostly deposited in the subcutaneous area rather than the visceral (Khera et al., 2009;Pausova, 2014).Skinfold thickness is also affected by age.In the older population, fat distribution decreases in the subcutaneous tissue and increases in the visceral (Nguyen et al., 2021).As it was reported in a study by Dwimartutie et al., (2009), the triceps skinfold thickness interval in subjects aged more that 60 years was 4-32 mm, which is lower than that found in this study.
In this study, the total daily dose of insulin multiple daily injections in T2DM patients used every day was recorded, without differentiating the type of insulin used.The average total daily dose used by the patients in this study was 40.9±18.01IU.Similar result was also found in another study in India, where the total daily dose of insulin used was 43.3±23.4IU (Kesavadev et al., 2013).The similarity of these results may be caused by the similarity of diets in Indonesia and India, where the common carbohydrate consumed is rice.Carbohydrate consumption is one of the factors that affect the insulin doses needed (Nourizadeh-Sedaghati et al., 2016).In another study by Reznik et al. (2014)  reported average total daily dose of insulin was 122±68 IU in T2DM patients with multiple daily injections.The high dose of insulin used compared to the results obtained in this study was due to the fact that the study subjects included were T2DM patients with uncontrolled blood glucose and insulin resistance, with an average total insulin dose of 1.1 IU/kg.In this study, there was a significant correlation (p <0.05) between triceps skinfold thickness and insulin total daily dose in T2DM patients at Dr. Soetomo General Academic Hospital with a moderate positive correlation (r=0.325).This correlation means that the thicker the subcutaneous fat or skinfolds, the higher the insulin dose needed per day.However, there are other factors that affect the insulin total daily dose besides the skinfold thickness.
The absorption of insulin from the subcutaneous tissue is affected by many factors.These factors create variability in the effects of insulin which will result in unpredictable therapeutic responses, inadequate glycaemic control, and an increased risk of hypoglycemia (Gradel et al., 2018).One example is insulin glargine, where the difference in the biological action of insulin is more influenced by its absorption in the subcutaneous tissue (Mudaliar et al., 2002).
In people with obesity, the high thickness of subcutaneous fat affects the reduced capillary density and reduces subcutaneous blood flow which causes slow absorption of insulin, which will also contribute to changes in the pharmacokinetics of insulin (Morello, 2011;Gradel et al., 2018).The results obtained in this study were consistent with those of Gradel et al. (2019) who conducted experiments on mice fed with high-fat and low-fat diets.In rats fed with high-fat diet, absorption of insulin Aspart after subcutaneous injection was slower than in rats fed with low-fat diet.This is caused by the smaller subcutaneous insulin depot after injection in mice fed with high-fat diet, where the smaller the injection depot, the slower the loss or absorption of insulin from the subcutaneous tissue.A study conducted by Hildebrandt and Vaag (1993) showed that skinfold thickness is directly proportional to the size of the CSII (continuous subcutaneous insulin infusion) insulin depot at steady-state.This suggests that insulin absorption is slower in patients who have higher skinfold thickness.Gagnon-Auger et al. (2010), who studied the pharmacokinetic differences of short-acting insulin analogs in obese T2DM patients, found that both the absorption and action of insulin lispro were greatly delayed at high doses (30 and 50 units).However, different results were found in the study of Clauson and Linde, (1995) which compared the absorption of rapid-acting insulin in obese and nonobese T2DM patients.In that study, no difference was found between absorption in obese and non-obese patients.This might happen because the average fat thickness of the study subjects was lower than this study.
In addition to obesity and subcutaneous fat thickness, subcutaneous insulin absorption is affected by other factors, such as injection site, temperature, physical activity, and differences in insulin types (Gradel et al., 2018).Various insulin injection sites have different absorption rates depending on the injection site.Insulin absorption is more rapid in the abdomen and deltoid than in the thighs and buttocks (Morello, 2011;Gradel et al., 2018).Bitton et al. (2019) compared the effects of heating and cooling at the injection site of insulin glargine and found that warming had an effect on increasing insulin absorption.This is possible because an increase in temperature causes vasodilation.Vasodilation caused by an increase in temperature can occur due to the effects of a vasodilator the NO (nitric oxide).NO is produced from the conversion of L-arginine to L-citrulline and NO that is catalyzed by NOS (nitric oxide synthase) (Förstermann and Münzel, 2006).There are 3 isoforms of NOS, namely nNOS (neural NOS), iNOS (inducible NOS), and eNOS (endothelial NOS).Local warming triggers eNOS (Kellogg et al., 2008), while heat stress applied to the whole body (whole body heat stress) triggers nNOS to produce NO (Kellogg et al., 2008).
Physical activity and exercise accelerate insulin absorption subcutaneously (Gradel et al., 2018).Study by Berger et al. (1982) also found that massage at the site of insulin injection and exercise increased the rate of insulin absorption.Heinonen et al. (2012) reported that during exercise, the blood vessels in the subcutaneous tissue that are close to the contracting muscles will be vasodilated due to the influence of the heat generated by the muscles.Rhythmic muscle contractions that occur during exercise are one of the stimuli for increased shear stress on the arterial circulation (Casey et al., 2017).Shear stress itself is a tangential force of blood flowing on the surface of the vascular endothelium (Paszkowiak et al., 2003).Shear stress induced by muscle contraction can increase the phosphorylation of eNOS, which in turn increases NO bioavailability (Casey et al. , 2017).

CONCLUSION
Subcutaneous fat thickness, as measured by skinfold thickness, is one of many factors that affect insulin absorption from the subcutaneous tissue.Therefore, more attention is needed to these factors in administering insulin doses to T2DM patients in order to avoid unwanted risks, such as the risk of hypoglycemia and not achieving the desired glycemic target.

Table 2 .
Subject's triceps skinfold thickness and insulin total daily dose Khan et al. (2020) characteristics of the subjects, it was found that the age group ranging from 50-59 years was the highest among other age groups.This was also found in another study byKhan et al. (2020)who studied the global epidemiology of T2DM, where most T2DM patients aged 55-59 years.The number of female subjects in this study was higher than males, despite the slight difference.Data from Riskesdas (2018) from the Indonesian Ministry of Health also stated that in Indonesia, diabetes was found higher in females.A different result was found in another study byKhan et al.  (2020) and Sun et al. ( conducted multicentred in Canada, Europe, Israel, South Africa, and the United States, the