Mid-arm muscle circumference: A significant factor of all-cause and cancer mortalities in individuals with elevated platelet-to-lymphocyte ratio

Platelet-to-lymphocyte ratio (PLR) is an inflammatory maker, and high PLR is associated with mortality in several diseases. The predictors of mortality in individuals with high PLR is still lacking. Our aims were to assess if mid-arm muscle circumference (MAMC) can predict all-cause mortality, cancer mortality, and cardiovascular mortality in individuals with high PLR. Adult participants from the National Health and Nutrition Examination Survey III (1988–1994) were included. All participants were divided into low PLR and high PLR groups with the cut-off point being the median PLR level, and each group was evaluated for risk factors of mortality. MAMC was divided into tertiles and the general characteristics of the study population related to MAMC were evaluated. The study included 14,221 adults with 6,701 (47.1%) male and 7,520 (52.9%) female participants. The median PLR ratio was 122. Higher levels of systolic blood pressure, total triglycerides, total cholesterol, low-density lipoprotein, C-reactive protein, uric acid, and glucose, as well as a higher age, were associated with increased risk of mortality in both groups. After adjusting for all the covariates, in the higher PLR group, the highest MAMC tertile was significantly associated with lower hazard ratios for all-cause and cancer mortalities compared with the lowest MAMC tertile. However, this association was not observed in the low PLR group. The highest MAMC tertile showed protective effects from all-cause and cancer mortalities compared with the lowest MAMC tertile in individuals with PLR ≥ 122. In conclusion, the highest MAMC tertile was significantly associated with decreasing HRs for all-cause and cancer mortalities compared with the lowest MAMC tertile in individuals with elevated PLR.


Introduction
The platelet-to-lymphocyte (PLR) ratio is a universally known indicator of systemic inflammation. Previous literature has demonstrated that higher PLR is associated with poor prognosis a1111111111 a1111111111 a1111111111 a1111111111 a1111111111

Data source and participants
The National Health and Nutrition Examination III (1988)(1989)(1990)(1991)(1992)(1993)(1994)) was a complex multi-stage stratified study managed by the National Center for Health Statistics (NCHS) of the Centers for Disease Control and Prevention (CDC) [8]. NHANES III was a program to evaluate the health and nutritional statuses with household interviews and physical examinations of noninstitutionalized adults in USA. It was conducted in accordance with the guidelines of the Declaration of Helsinki. A subsample of participants aged 20-90 years was identified from it with a mean follow-up of 14.3 years. The survey design and procedures (questionnaires, examinations, and laboratory components) of NHANES III are publicly available online at http://www. cdc.gov/nchs/nhanes.htm.

Follow-up data on all-cause mortality, cancer mortality, and cardiovascular mortality
The mortality data of the NHANES III study is from a probabilistic match between NHANES III and the National Death Index (NDI) records. NDI is available publically and contains deidentified death-certificate data, updated through 31 December 2006.
The cause of death was identified according to the guidelines of the International Statistical Classification of Disease, Injuries and Causes of Death; the 9th revision was used for those who died before 1999 and 10th revision for all others. NHANES procedures harmonized the differences in definitions and causes of death, all of which have been demonstrated to be comparable.
We included deaths from all causes; we included deaths due to malignant neoplasms, which were coded from C00-C97 in the International Classification of Diseases, 10th Edition (ICD-10) for cancer specific mortality, while for cardiovascular (CV) mortality, we included diseases of the heart and circulation system (ICD-10 = I00-I178).
The data of MAC was collected according to the standard procedures defined by Lohman and colleagues and was based on the age of the participant [9]. They were divided into tertiles and the lowest tertile was used as the reference group. All participants were divided into low PLR and high PLR groups with the cut-off point being the median PLR level, and each group was divided into three subgroups (lowest, middle, and highest) based on their MAMC level. The tertiles were as follows: T1 (

Covariates
The participants were interviewed for self-reporting of general characteristics and previous medical histories regarding the following variables: age, race/ethnicity, sex, smoking status, and physician-diagnosed previous clinical illnesses (congestive heart failure-CHF, stroke, asthma, malignancy, and type 2 diabetes mellitus-DM). Diabetes was defined as self-report history, fasting plasma glucose � 126 mg/dL, OGTT 2-h plasma glucose � 200 mg/dL, or random serum glucose � 200 mg/dL. The biochemistry profiles were collected from the blood samples, which were then assessed by the Lipoprotein Analytical Laboratory at Johns Hopkins University, Baltimore, Maryland, USA. The plasma glucose level was assessed via the hexokinase enzymatic method. Serum total cholesterol (TC), triglycerides (TG), high-density lipoprotein (HDL), and low-density lipoprotein (LDL) levels were measured using the Hitachi 704 Analyzer, and serum C-reactive protein (CRP) levels were measured using latex-enhanced nephelometry. Other biochemical profiles, such as serum albumin, aspartate transaminase (AST), alanine transaminase (ALT), uric acid (UA), and total bilirubin were measured by using Beckman Synchron LX20.

Statistical analysis
The statistical analyses were performed using SPSS version 18 (SPSS, Inc., Chicago, IL, USA). Continuous data were compared using the Independent t-test or Wilcoxon Rank sum test, and presented as means ± standard errors (SE). Categorical data were compared using the Chisquare test and presented as number and percentages (%). The p values of less than 0.05 were considered to be statistically significant.
The association between MAMC tertiles and all-cause, cardiovascular, and cancer mortalities were evaluated by Cox proportional hazard models. An extended-model approach was used for adjusted covariates. Model 1 was not adjusted for any variables; model 2 was adjusted for race, sex, and body mass index (BMI); model 3 was adjusted for the variables in model 2 and systolic blood pressure, serum triglycerides, and serum fasting glucose; and model 4 was adjusted for the variables of models 2 and 3, and smoking, congestive heart failure, stroke, gout, and malignancy.

Ethics statement
The National Center for Health Statistics Institutional Review Board approved the NHANES III study, and all participants in the NHANES III provided written informed consent. This study was exempt from IRB review because we analyzed an open available online database. All methods in this study were performed based on the relevant guidelines and regulations.

Results
The study included 14,221 adults with 6,701 (47.1%) male and 7,520 (52.9%) female participants. The median PLR ratio in this population was 122. The participants were divided into two groups; low PLR group (PLR<122) and high PLR (PLR�122) group. The mean MAMC was 26.3 ± 3.9 cm and mean age was 47.5 ± 18.7 years in the lower PLR group. The mean MAMC was 25.6 ± 3.8 cm and the mean age was 47.8 ± 19.4 years in the high PLR group. In our study, the mean follow-up duration was 14.3 years.
The clinical characteristics of the participants of the low PLR group related to mortality are depicted in Table 1. In this group, higher levels of age, systolic blood pressure (SBP), diastolic blood pressure (DBP), and serum levels of TG, TC, LDL, CRP, total bilirubin, UA, glucose, and AST were associated with increased risk of mortality. Other factors that were associated with increased risk of mortality included male sex, non-Hispanic white ethnicity, and associated conditions like congestive heart failure, stroke, asthma, malignancy, diabetes mellitus, and smoking. However, higher serum levels of HDL, albumin, and ALT were associated with decreased risk of mortality.
The clinical characteristics of the participants of the high PLR group related to mortality are depicted in Table 2. In this group, higher levels of age, SBP, and serum TG, TC, LDL, CRP, UA, and glucose were associated with increased risk of mortality. Additional factors that Table 1. Characteristics of participants with low platelet-to-lymphocyte ratio (<122).

Characteristics of Study Participants
Non increased the risk of mortality included male sex, non-Hispanic white ethnicity, and conditions such as congestive heart failure, stroke, asthma, malignancy, diabetes mellitus, and smoking. However, high levels of BMI, and serum albumin and ALT were associated with decreased risk of mortality. Table 3 presents the clinical characteristics of the participants of the low PLR group related to MAMC tertiles. In these participants, higher levels of BMI, SBP, DBP, TC, TG, LDL, total bilirubin, UA, glucose, albumin, AST, and ALT were associated with higher MAMC tertiles. However, higher levels of HDL were associated with lower MAMC tertiles. Higher percentages of male participants and those with diabetes mellitus and smoking were associated with higher MAMC tertiles. Higher percentages of non-Hispanic white participants were associated with lower MAMC tertiles. Higher levels of age and higher percentages of congestive heart failure and malignancy were found in the second tertile of MAMC. Table 4 shows the clinical characteristics of the participants of the higher PLR group related to MAMC tertiles. In these participants, higher levels of BMI, DBP, and serum TG, LDL, total bilirubin, UA, glucose, albumin, AST, and ALT were associated with higher MAMC tertiles. However, higher HDL was associated with lower MAMC tertiles. Higher levels of age, SBP, and serum TC and CRP were found in the second tertile of MAMC. Higher percentages of male participants and those with smoking habit were associated with higher MAMC tertiles. Higher percentages of non-Hispanic white participants and those with malignancies were associated with lower MAMC tertiles. The maximal percentage of patients with congestive heart failure, stroke, and diabetes mellitus were found in the second tertile of MAMC. We further investigated the relationship between MAMC and all-cause mortality, cancer mortality, and CV mortality according to the low and high PLR values. The results of multivariable adjusted analyses for all-cause mortality, cancer mortality, and CV mortality associated with MAMC in the two PLR groups are shown in Table 5. After adjusting for all the covariates (model 4), in the high PLR group, the highest MAMC tertile was significantly associated with decreasing hazards ratios (HRs) for all-cause and cancer mortalities compared with the lowest MAMC tertile. However, this association was not observed in the low PLR group. Furthermore, higher MAMC tertiles were not significantly associated with decreasing CV mortality after adjusting for covariates in both the groups.

Discussion
PLR is an inexpensive and routinely available valuable maker for nonspecific inflammatory conditions [10]. Previous reports have shown that inflammation plays a critical role in cancer progression [11],coronary artery disease [12], chronic kidney disease [13], heart failure [14], and all-cause mortality [15]. Recently, studies demonstrated that PLR is an inflammatory biomarker, prognostic factor, and mortality predictor in patients with malignancy, cardiovascular diseases, and end-stage renal diseases [1][2][3][4]. The mechanisms of the influence of PLR on prognoses in patients with malignancies, cardiovascular diseases, and end-stage renal disease is still incompletely understood. The increased inflammatory response may promote production of acute phase proteins and cytokines, and lead to the differentiation of megakaryocytes into platelets [16][17][18]. Platelets play a critical role in thrombosis and inflammation. The increased platelet counts may lead to the release of pro-inflammatory cytokines and further result in a pro-thrombotic state, which will lead to further platelet activation and thrombosis [19][20]. Platelets also play a critical role in cancer cell proliferation and migration through production of metalloproteinases and growth factors [21][22]. Lymphocytes also play a major role in inflammation; under stressful conditions, the activation of hypothalamic-pituitary-adrenal axis results in secretion of cortisol, which results in decreased lymphocyte count [23][24].
Since the relationships between high PLR, mortality, and clinical outcomes in several diseases have been proven, we should attempt to identify the potential factors to decrease the mortality in individuals with high PLR. Patients with lower MAMC may have reduced lean muscle mass and decreased muscle strength, which may be due to decreased physical activity or an underlying medical disease [7,25]. In previous studies, MAMC has been demonstrated to be associated with physical function, life quality [7], male all-cause mortality [26], and mortality in patients on hemodialysis [5]. In our study, we examined a nationally demonstrative sample of American adults to determine whether MAMC influences mortality outcomes in low and high PLR groups. We observed a statistically significant decrease in the HRs for all-cause and cancer mortalities in the highest MAMC tertile compared with those in the lowest MAMC tertile after adjusting for covariates; however, this association was not observed in the low PLR group. Individuals with high PLR are believed to be in a state of systemic inflammation and one of the reasons for our results is that higher MAMC may have a protective effect from mortality in such individuals. However, patients with lower MAMC may be suffering from weakness, chronic illness, or malnutrition; therefore, the underlying condition may result in a higher mortality rate in individuals with chronic inflammation. Previous studies reported that physical performance was associated with MAMC [27] and physical activity may aid in the prevention and treatment of sarcopenic obesity [28]. As mentioned above, proper exercise may help control inflammation, and it plays an important role in lowering the mortality risk in individuals with high PLR. Routine exercise maintains muscle mass and strength, and it also improves inflammatory conditions by reducing the levels of pro-inflammatory cytokines [29][30][31]. Therefore, we may suppose that proper exercising modulates inflammation and leads to decreased mortality risk in the population with high PLR.
There are several limitations to our study. First, the cross-sectional nature of our survey and the fact that the anthropometric and blood examination data were collected only at the followup time may have resulted in bias. Second, the large amount of data was collected from selfreporting and, therefore, maybe have a recall bias. Third, even after adjusting for many confounding variables, some confounding bias may still be present. Fourth, the native design of NHANES database is not fit for a global population.

Conclusion
In conclusion, the highest MAMC tertile was significantly associated with decreasing HRs for all-cause and cancer mortalities compared with the lowest MAMC tertile in individuals with PLR � 122. Clinical care should focus on maintaining muscle mass and muscle strength by means of increasing physical activity and controlling the underlying chronic inflammatory disease to decrease the mortality rate. Future studies should focus on the longitudinal investigation of the changes in MAMC and the change in the influence of MAMC on mortality in individuals with high PLR.