Several studies have suggested that the upper limit of normal aminotransferases should be revised [1,2]. In the past seven years, several approaches have been made to establish new reference intervals or thresholds for liver enzymes in children [3-7], but most of these were for Western population. With the assumption that the current reference range for amino-transferases may need revision, we conducted this study to evaluate the normal values of aminotransferases in school children aged 2-18 years.

This school-based cross-sectional study was carried out in Jaipur in the year 2019 after institutional ethics committee clearance. Three schools were selected randomly from rural areas and two schools from urban areas of Jaipur, Rajasthan. Study population included children aged 2-18 years, after parental written consent. A total of 590 children and adolescents were initially screened. During the screening, participants were asked a comprehensive questionnaire regarding their basic demographic information, medical history including current history of febrile illness, medication use (including ayurvedic, growth and apetite stimulators) and social information which included age, sex and history of previous liver disease. Clinical history and general physical examination was done based on a predefined proforma. Height, weight and triceps skin fold thickness (by skinfold caliper) were measured. Five milliliter of non-fasting venous blood sample was collected and processed within 4 hours. We excluded 149 study subjects (active viral upper respiratory infection, 14;HBsAg positive, 5; IgAtTG positive, 7; those with aminotransferses values >3 standard deviation, 16; BMI less than 10th percentile, 50; BMI 90th percentile, 57) [7]. Finally, aminotransferases levels of 441 subjects (165 males) were analyzed.

Student t test and ANOVA (one-way analysis of variance) test followed by post hoc test were used for comparing the difference between the various groups. Pearson correlation was conducted to examine the relationship between aminotransferase levels and various parameters like age, sex, body mass index (BMI), triceps skin fold thickness etc.

Mean (SD) age of study subjects was 12.3 (7.4) years, and for analysis, we divided study subjects to different age groups (2-5, 6-8, 9-11, 12-15 and 16-18 years) with 22, 57, 77, 195, and 90 study subjects in each age group, respectively. Median (IQR) AST and ALT values in study subjects were 30 (27- 34) U/L and 23 (19-29) U/L (Table I). However, Poustchi, et al. [3] reported median ALT for boys and girls to be 16 U/L and 13 U/L which were quite lower than our median ALT values. The difference between sexes was statistically significant, similar to previous studies [4,7]. We found upper limit of normal (97th percentile) AST and ALT to be 44 U/L and 40 U/L, which were somewhat similar to as described by England, et al. [4] 40 and 35, respectively, but were higher than those reported by Dehghani, et al. [5] (29 and 21, respectively).

We observed peak of median AST serum values in age group 6-8 years followed by continuos decline with increasing age. However in a study by Bussler, et al. [7], the AST serum values were showing peak at age group 1-3 years followed by continuos decline with increasing age. While in ALT, we observed maximum values in age group 2-5 years followed by continous decline and we did not find any peak around puberty. The initial decrease in ALT has also been described by previously [4], and apart from the missing ALT peak in early puberty in boys, Zierk, et al. [6] presented similar patterns of ALT with age. However, others reported initial fall in ALT with increasing age followed by peaking around puberty [7].We found that both AST and ALT were significantly negatively related to age (P<0.001). Bussler, et al. [7] showed that AST also decreases with increasing age, with no significant effect of age on ALT. Reverse association of ALT increase with increasing BMI, with weak negative association with AST was previously reported [7], but we did not observe such an association.

We provide age- and sex-related percentiles of amino-transferases of children from a limited data set from a single center in Northern India. In addition to the small sample size, our sample was not equally distributed between males, females and different age groups, so it was not representative of the population. Also, our data cannot be generalized to others parts of the country. We did not use ultrasound or fibroscan to exclude pediatric non-alcoholic fatty liver disease (NAFLD). We didnot do C-reactive protein levels to exclude occult sepsis. Tanner staging was not done to see effect of puberty on transaminases. We did not take into account the other factors like timing of day, effect of exercise and day to day variation of aminotransferases. However, our findings underscore the need for large multi-centric studies to document normal aminotransferase levels children.

Contributors: SN, GKG: Concept and designed the study; SR, SS, GKG: Analyzed data and drafted the manuscript; SR, KD: Collected the data and helped in data analysis.

Ethics clearance: IEC, SMS medical college; No 64IMC/RC/2019, dated November 15, 2019.

Funding: None; Competing interests: None stated.

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2. Kariv R, Leshno M, Beth-Or A, et al. Re-evaluation ofserum alanine aminotransferase upper normal limit and its modulating factors in a large-scale population study. Liver Intr. 2006;26: 445-50

3. Poustchi H, George J, Esmaili S, et al. Gender differences in healthy ranges for serum alanine aminotransferase levels in adolescence. PLoS One. 2011;6:e21178.

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5. Dehghani SM, Erjaee A, Haghighat M, Imanieh MH, Ahmadi R. Upper limits of normal aminotransferases in children in Southern Iran. J Compr Ped. 2014;5:15274.

6. Zierk J, Arzideh F, Rechenauer T, et al. Age- and sexspecific dynamics in 22 hematologic and biochemical analyses from birth to adolescence. Clin Chem. 2015;61:964-73.

7. Bussler S, Vogel M, Pietzner D, et al. New pediatric percentiles of liver enzyme serum levels (alanine aminotransferase, aspartate aminotransferase, gamma glutamyl transferase): Effect of age,sex, body mass index and pubertal stage. Hepatology. 2018;68: 1319-30.