Prevalence of Elevated Serum Aminotransferases among Asymptomatic Population of Tamil Nadu , India

Studies carried out across several countries have shown that serum aminotransferases levels vary with various clinical and demographic factors such as age, sex, race, body mass index (BMI) etc. Our objectives were to estimate the prevalence of elevated serum aminotransferases among asymptomatic individuals in the population in Tamil Nadu, the southern region of India and also to identify the associated risk factors for the same. A total of 10765 individuals were included in this population-based study. Subjects were requested to report on an empty stomach in the morning and blood samples were collected. Those subjects who did not report were visited in their homes and blood collected. Subject’s demographic, clinical and laboratory data such as serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), cholesterol, triglycerides, glucose, HDL cholesterol were analyzed. Univariate and multivariate logistic regression was done to calculate odds ratio with 95% confidence intervals. Among the 10765 participants, 18.0% (1938) had elevated aminotransferase. High proportion of elevated aminotransferase was seen in males (20.2%) compared to females (15.7%) (p < 0.0001). Univariate analysis showed a significant association of hypertriglyceridemia, hyperglycemia, diabetes mellitus, age and BMI with elevated aminotransferase in both genders. Multivariate analysis revealed that age, hypertriglyceridemia, hyperglycemia and BMI may be independently associated with elevated aminotransferase in both genders. This study revealed that 18% of the asymptomatic individuals in Tamil Nadu, South India had laboratory findings suggestive of possible liver damage. Middle aged and obese individuals having hypertriglyceridemia and hyperglycemia should be screened for elevated aminotransferase and clinically evaluated further for potential liver damage.


INTRODUCTION
Liver diseases are a significant health burden due to their increasing morbidity and mortality rates worldwide.In the majority of the cases, a long and asymptomatic pathogenic duration of chronic liver diseases (CLD) leads to the end stage liver diseases such as cirrhosis, hepatocellular carcinoma (HCC), etc., 1,2 .The major risk factors for CLD and end stage liver diseases include excess alcohol consumption 3 , hepatitis B or hepatitis C virus infection (4), Non-alcoholic fatty liver disease (NAFLD) 5 .However, several studies have shown that causes of cirrhosis remains cryptogenic in many individuals.Indeed, prevalence of liver diseases and diverse etiologies are closely related to different geographical regions and populations hygienic, sanitary conditions, sedentary lifestyles and other indicators of the level of socioeconomic status 6 .In particular, NAFLD is emerging as one of the most important causes of CLD in various countries [7][8][9] .Understanding the causes of liver disease and its future projections is critically important for the planning of care pathways and the provision of healthcare.
Chronic liver disease is often diagnosed by asymptomatic elevations in serum aminotransferases, which include alanine aminotransferase (ALT) and aspartate aminotransferase (AST), as these are usually sensitive indicators of liver-cell injury and are helpful in recognizing CLD (10).Most of the published epidemiological studies on the prevalence and etiology of elevated aminotransferase levels have only been documented in restricted groups such as blood donors 11 , health screening 12 , primary care center 13 and in overweight and obese adolescents 14 .Moreover, changing lifestyle habits, food habits and urbanization in the recent times have increased the incidence of obesity in India.Several studies from different countries had shown variation in serum aminotransferases levels to be associated with various clinical and demographic factors such as age, sex, race, body mass index (BMI) etc. 15,16 .
A population based screening of liver function test could provide a reliable tool to estimate the potential chronic liver diseases.However, to our knowledge, such a study has not been conducted on liver function test in Tamil Nadu, South India.This is the first population-based study and aims to determine the prevalence of elevated serum aminotransferases in asymptomatic individuals in a large population in urban, sub-urban and rural areas of southern region of India and identify associated risk factors.

Study Design and Target Population
A large population survey was carried out for screening of liver disease among the South Indian population in the period of 2013 to 2016 by the Department of Hepatology, Madras Medical College, Chennai.The study protocol has been approved by the Institutional ethics committees.Randomly selected areas of urban, rural and suburban regions of Tamil Nadu South India were included (Pannaipuram in Theni district, Royapuram, Madhavaram, Porur, Poonamalle areas of Chennai District, Tambaram area of Kanchipuram District, Uthukottai, Velliyur, Manavur, Periyapalayam, Palavedu areas of Tiruvallur District, Sholurmattam of Nilgris District and Vellore District).The local population was informed a day before of conducting the study via press, loud speaker and local newspapers.

Screening
A written informed consent was obtained from each participant.During the screening, participants were asked to complete a comprehensive questionnaire regarding their basic demographic information, medical history, medication use and social information which includes age, sex, alcohol intake, history of diabetes, history of hypertension and history of previous liver disease.Heights and weights were measured and body mass index was calculated.Subjects were excluded during the analysis if they had a known history of viral hepatitis, any other liver disease, alcoholic (consumed >20 g/ day) or an identified cause of LFT elevation (ie, drug toxicity).

Biochemistry
Five millilitres of fasting venous blood sample was collected in the morning from all individuals who participated in sterile dry syringes.All blood tests were undertaken within a few hours of sampling.Blood samples were tested for serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), cholesterol, triglycerides, serology for viral hepatitis.In our analyses, ALT levels were considered to be abnormal if they exceeded 31 IU/L (men), 24 IU/L (women); AST levels were considered to be abnormal if they exceeded 37 IU/L (men), 31 IU/L (women); these values are consistent with the upper limits of normal established by our lab.

Statistical Analysis
Data for continuous variables were expressed as mean ± SD and categorical variables were expressed as frequencies.The continuous variables were evaluated by Student's t-tests and categorical variables were evaluated by Pearson's chi-square test.P value of less than 0.05 was considered to be significant as the distributions were normal.To identify variables associated with elevated aminotransferases crude and adjusted odds ratios (ORs) were calculated using univariate and multivariate logistic regression analyses.Only those variables that were statistically significant effect at the 0.05 level in the univariate analyses remained in the multivariate model.Ninety-five percent confidence intervals (CIs) were also determined.All statistical calculations were conducted using SPSS version 20.0.

Abnormal liver function tests
The distribution of the different possible causes of elevated aminotransferase by demographic characteristics and other factors were shown in Table 2. Overall, 18.0% had elevated aminotransferase (1938 out of 10765 subjects).The abnormal aminotransferase was very high in male gender (20.2%) when compared to female gender (15.7%) (p < 0.0001).The aminotransferase elevation was very high between the age group of 41 -50 years (33.9%).This was followed by the age group of 31 -40 years (16.5%) and minimal level were observed among the individuals falling below the age group of 20 years (9.7%) (p < 0.0001).However, elevated aminotransferase increased gradually with increasing BMI (p < 0.0001).The elevated aminotransferase was higher in urban populations (21.6%) than suburban (19.6%), rural (13.3%), tribal (6.8%) (p< 0.0001).
We conducted further analyses to determine specific characteristics associated with asymptomatic aminotransferase elevations in male gender and female genders (Table 3-6).Male with elevated aminotransferase were slightly younger (p < 0.004) and were having higher BMI when compared to that of males with normal aminotransferases (p < 0.001).On the other hand, compare to males, females with asymptomatic aminotransferase elevations were in the slightly higher age (p < 0.006).Similar to male, female with asymptomatic aminotransferase elevations had higher BMI (p < 0.001), higher number of increased fasting triglyceride levels (p < 0.001), number of diabetics (p < 0.001) and glucose levels (p < 0.001).
Neither history of hypertension nor total and HDL cholesterol levels were shown to have significant association in both the genders.
Univariate analysis had shown that there was a significant association in age, hypertriglyceridemia, hyperglycemia, diabetes mellitus and BMI with elevated aminotransferase in both genders, however, multivariate analysis had revealed that age, hypertriglyceridemia, hyperglycemia and BMI may be the common independent predictors of elevated aminotransferase.Diabetes mellitus was again significant risk factors for males but not females.

DISCUSSION
Majority of the epidemiological studies on liver diseases were conducted in a highly selected hospital based populations and this leads to referral bias.To avoid such bias in the studies related to the liver diseases, we have assessed the elevations in the levels of aminotransferases and its etiology among population of a South India, Tamil Nadu; such a population has dietary and cultural habits that are different from those of populations in northern India and other states of Indian country.
In the present study, we found a high proportion of elevated serum aminotransferase levels (18.0%) in the population of South India, Tamil Nadu including 20.2% of male gender, 15.7% of female gender.
To our knowledge, this is the first and largest cross-sectional population based study to analyze the level of aminotransferases among the population of south India.A study from Punjab showed that the elevation of serum aminotransferases was found in 46.15% of non insulin dependent diabetes mellitus patients 17 .In our study the observed high proportion 18.0% of elevated serum aminotransferase levels were relatively lower among the population without any symptom of the disease.
The causes of elevated aminotransferases may vary across different geographic areas which has been supported by the data obtained in our studies.The level of aminotransferase varied significantly between the two genders in the present study.Our present study revealed that male subjects had high proportion of elevated aminotransferase.Hypertriglyceridemia, hyperglycemia, metabolic factor ie., body mass index were associated with elevated serum aminotransferase in both genders.However, gender differences have been reported in different studies worldwide including Japan 18,19 , USA in various ethnicity 20,21 .Similar to our result, previous Asian studies also could not the find gender based differences in BMI for liver enzyme elevation 22 .However, we found that aminotransferase levels very high among middle aged 41-50 individuals in both genders and they are 4 to 5 fold more prone to develop liver disease.These important findings were not observed in other studies.This clearly explained that aminotransferase levels may vary by race and ethnicity.Hence, we conclude that this could be due to South Indian origin and might be different for other ethnicities.
However, it should be stressed that in both men and women, asymptomatic aminotransferase elevation is strongly associated with excess BMI, one of the possible abnormalities related to the asymptomatic elevation of liver function test.We s u s p e c t t h a t m o s t c a s e s o f aminotransferase elevations may be caused by nonalcoholic fatty liver disease (NAFLD).To support this, aminotransferase elevations was significantly associated with hypertriglyceridemia, hyperglycemia, diabetes and which is consistent with other studies on NAFLD 23 -25 .However, we did not find an association between aminotransferase elevations hypercholesterolemia and HDL cholesterol, as seen in prior studies.

CONCLUSIONS
The results of this population-based survey indicate that a high proportion of the population in a Tamil Nadu, South India has laboratory findings suggestive of possible liver damage even though they are asymptomatic.Hypertriglyceridemia, hyperglycemia and excess BMI in the middle age is becoming an increasingly important etiological factor for individuals with elevated aminotransferase.It may be suggested based on these findings that obese individuals with diabetes and hypertriglyceridemia should be investigated for liver damage and managed accordingly.

Table 1 : Data distribution of age, body mass index, laboratory values among the study subjects
*The continuous variables are mean±sd and categorical variables are frequency.t test for continuous variables or chisquared test for categorical variables (*P<0.05)

Table 2 : Proportion of elevated aminotransferase levels in the Tamil Nadu population by various demographic, body mass index and laboratory characteristics
The continuous variables are mean±sd and categorical variables are frequency.t test for continuous variables or chi-squared test for categorical variables (*P<0.05)

Table 3 : Demographic and Laboratory Characteristics of Male by Elevation of Aminotransferase
The continuous variables are mean±sd and categorical variables are frequency.t test for continuous variables or chi-squared test for categorical variables (*P<0.05)

Table 4 : Demographic and Laboratory Characteristics of Female by Elevation of Aminotransferase
The continuous variables are means±sd and categorical variables are frequency.t test for continuous variables or chi-squared test for categorical variables (*P<0.05)

Table 6 : Multivariate logistic regression analysis to evaluate the association of risk factors predicting elevated aminotransferase
*Significant by logistic regression analysis (*P<0.05).