Introduction
erum alanine aminotransferase (ALT) concentration is
the most commonly-used variable for assessment of the risk of mortality in
liver disease.1,2 The current mean upper normal limit (UNL) for ALT
was 40 (range: 30 – 50) U/L in previous studies.1,3–8 Such
thresholds were introduced when ALT testing was a surrogate marker for the screening of non-A non-B
hepatitis among blood donors and before antihepatitis C virus (HCV) testing,
and restrictive behavioral criteria for donor selection were implemented.
The so-called “reference” population was
likely to include many persons with nonalcoholic fatty-liver disease (NAFLD),
now recognized as the most prevalent cause of chronic liver disease in
developed countries.9–11 The current reference ranges for ALT levels
probably underestimate the frequency of chronic liver disease.
The UNL varies in different laboratories
according to the commercial kit used and the reference population chosen by
each manufacturer to establish the normal range. In Iran, no UNL has yet been
established in a large-scale population-based study, despite its importance as
an aid to the classification and management of patients with liver diseases.
Recent studies have shown that serum ALT
levels can be modulated by a number of factors, including gender, body mass
index (BMI), fasting blood glucose, and serum triglyceride levels.12–14
These factors are usually not taken into account when the normal ALT range is
determined. Considering the fact that serum ALT level varies in different
populations, this study was undertaken in an Iranian general population for the
first time.
Materials and Methods
Golestan Province is located in northeast Iran with 1,700,000 populations.
Gonbad and Kalaleh are located in Golestan Province. Gonbad has a population of
437,960 and the population of Kalaleh is 154,349.
In autumn 2006, a total of 2,292 (1,376
females, aged 18 – 75 years) inhabitants of villages and cities of Gonbad and
Kalaleh were randomly selected by systematic clustering, according to the house
hold number in the health houses, and were invited to take part in this study.
The protocol used in the present study was approved by the Ethical Committee of
the Digestive Disease Research Center at Tehran University of Medical Sciences
based on the Declaration of Helsinki.
The participants were informed about the
objectives of the study. A written informed consent was obtained and a
comprehensive questionnaire including history of known hepatic disease,
medications used currently or during the last six months, hypertension, and
diabetes mellitus, was completed by a trained physician interviewer. Morning
blood samples of each participant were collected and transferred to Iranian Blood Transfusion Organization Research Center under appropriate condition. Separation
of serum was done under aseptic conditions. The sera were checked for ALT, hepatitis
B surface antigen (HBs Ag), and hepatitis C virus antibody (HCV Ab). The sera were
tested for ALT level using Hitachi autoanalyzer 704 (Roche, Switzerland) with Pars Azmoon reagents kit (Tehran, Iran). HBs Ag was measured by Enzygnost HBs Ag
5.0 kit (Dade Behring, Germany). HCV Ab was detected by enzyme-linked immunosorbent
assay (ELISA) method using Anti-HCV-EIA-Avicenna kit (Moscow, Russia). HCV
recombinant immunoblot assay III using INNOLIATM HCV-Score kit (Innogenetics, Gent, Belgium) was carried out on the positive samples of HCV by ELISA method. Those who
had positive HCV recombinant immunoblot assay III test were considered as exposed
to HCV. BMI was calculated by dividing weight in kilogram to the squared height
in meter. We considered a BMI≥25 kg/m2 as overweight.15
Diabetes mellitus and hypertension were defined if the participant was a known
case of those diseases (diagnosed by a physician, received medications, or had
nutritional restrictions). UNL introduced by the manufacturer for ALT kit was
40 U/L. UNL of serum ALT was considered as 95th percentile for the
serum ALT level, and was measured separately considering gender, BMI, and
diabetes mellitus status. All data were analyzed by SPSS software, version 13 (Chicago, IL, USA). Proportions were compared by Chi-square test. Multivariate analysis was
performed to identify factors independently associated with serum ALT>40 U/L.
P values <0.05 were considered statistically significant.
Results
Of the invited individuals (2,292), 698 out
of the 916 males and 1,351 out of the 1,376 females participated in the study
(participation rate: 76.2% and 98.1%, respectively). One hundred and twenty-one
participants were excluded due to positive HBs Ag, positive HCV Ab, and/or
drinking more than 20 grams of alcohol per day.
A total of 1,928 participants (1300 females)
were included. The mean age of the participants was 40.7±14.7 (range: 18 – 75)
years. The mean serum ALT level was 20.48±13.1 U/L and the mean BMI was
26.12±5.09 kg/m2.
The mean serum ALT level was significantly
higher in males (23.03±13.93 U/L) than females (19.24±12.5 U/L) (P<0.001);
in subjects with BMI≥25 (22.94±14.27 U/L) than those with BMI< 25
(17.51±10.82 U/L) (P<0.001); and also in diabetics (28.70±19.93 U/L)
than nondiabetics (20.12±12.62 U/L) (P<0.001). Table 1 indicates UNL
for serum ALT level considering BMI and diabetes mellitus in total study sample
and also separately according to gender.
|
Table 1. The upper normal
limit for serum alanine aminotransferase levels considering body mass index
and diabetes mellitus status.
|
|
Status
|
|
UNL for serum ALT levels (U/L)
|
|
|
Male
|
Female
|
Total
|
|
BMI<25
kg/m2 and nondiabetics (n=859)
|
37.5
|
36
|
36.1
|
|
BMI<25 kg/m2 (n=875)
|
37.85
|
36
|
36.2
|
|
BMI ≥ 25 kg/m2 (n=1053)
|
59
|
45.25
|
51
|
|
Diabetics (n=79)
|
51
|
80.5
|
77
|
|
Diabetics and BMI ≥25 kg/m2 (n=63)
|
60
|
85
|
79.4
|
|
Nondiabetics (n=1849)
|
48.5
|
39.85
|
45
|
|
Total
(n=1928)
|
50.55
|
41.95
|
45
|
|
UNL=upper normal limit; ALT=alanine
aminotransferase; U/L=unit per liter; BMI=body mass index; kg/m2=kilogram
per square meter.
|
Figure 1 shows the correlation between
serum ALT level and BMI in men and women.
|
|
|
Figure 1. Association between
serum alanine aminotransferase levels and body mass index in males and
females.
|
Logistic regression analysis showed that
male gender (OR=2.05; 95%CI: 1.44 – 2.94), BMI≥25 (OR=2.76; 95%CI:
1.84 – 4.13), and diabetes mellitus (OR=2.96; 95%CI: 1.56 – 5.61) were
independent risk factors for serum ALT level>40 U/L. Hypertension did not
have any correlationwith serum ALT level.
Discussion
Serum ALT level, a sensitive indicator of
liver cell injury, has been used to identify patients with liver disease for
almost 50 years.3 It has been recently suggested as a predictor of
overall mortality and medical costs.16 Several studies have recently
questioned whether the previously-established values for normal ALT range are
still accurate. They have suggested that the upper limit of normal range should
be revised.12–14 To the best of our knowledge, this is the first
population- based study conducted in Iran that determined the UNL for serum ALT
level. A previous study conducted in Iran on 1939 blood donors showed that UNL
in Iranian blood donors was 40 U/L in men and 34 U/L in women.12
However, the sample studied was not representative of the general
population. Blood donors in Iran are volunteers with healthy behaviors and
usually do not include obese or underweight subjects, alcohol or medication
users, or those with severe chronic diseases.
A large-scale population-based study by
Kariv et al. showed that the UNL of serum ALT level in a subgroup of the study
sample who had normal triglyceride, cholesterol, glucose, negative viral and
autoimmune markers, normal BMI, and those who used no hepatotoxic drugs or
alcohol (37.5 U/L) was lower than the UNL calculated in total study sample
which was selected at random from the general population (50.1 U/L).13
Prati et al. calculated the “healthy”
range for serum ALT level in blood donors who had a normal BMI and normal serum
cholesterol, triglyceride, and glucose levels and were not taking medications.
The calculated UNL for ALT level decreased from 40 U/L to 30 U/L in men and
from 30 U/L to 19 U/L in women.14 In this study, after excluding the
subjects with overweight or diabetes, the UNL of serum ALT level was
significantly lower than the total study group (36 versus 45 U/L). This finding
is comparable to the previous studies.13,14
Considering the high prevalence of over-
weights (54.6%) in our study, which is comparable to the previous studies
conducted in this area,17,18 the calculated UNL for the whole study
sample (45 U/L) cannot be used as the UNL for healthy individuals. The UNL
calculated for the subgroup of the study sample with BMI<25 kg/m2
(36.2 U/L) was lower than that for the total study sample and even the current
upper thresholds (40 U/L) proposed by the ALT kit manufacturer.
The UNL in those with normal weight and
non-diabetic individuals (men: 37.5 U/L; women: 36 U/L) was near to the
previously reported UNL for Iranian blood donors (men: 40 U/L; women: 34 U/L).12
The results also showed that UNL in non-diabetics (45 U/L) was lower than
diabetics (77 U/L). This most probably reflects the effect of diabetes mellitus
as a component of metabolic syndrome by inducing NAFLD on serum ALT level. There
is evidence showing that abnormal carbohydrate metabolism results in elevation
of serum ALT level.14,19–20
In this study, the UNL for serum ALT level
was significantly higher in overweight males than females (59 versus 45.25 U/L).
This is comparable with the previous study showing the more strong effect of
overweight in males in increasing the serum ALT level than in females.21
The previous study for determining UNL in Iranian blood donors also clarified
that serum ALT level was independently associated with BMI and male gender. And
association of ALT with BMI was more prominent in males than in females.12
Our study also determined the correlation
between serum ALT levels and male gender, BMI≥25 kg/m2, and
diabetes mellitus. It showed new thresholds for the UNL of serum ALT level according
to gender, BMI, and the presence of diabetes mellitus. This study further
emphasized the findings of the previous studies regarding the strong
association of serum ALT level with male gender and BMI.12,14,22–25
Diabetes mellitus and overweight are both
components of metabolic syndrome. NAFLD is the hepatic manifestation of
metabolic syndrome and the commonest etiology of elevated serum ALT level in
Iran.26,27 This explains the observed elevation of serum ALT level
in overweights and diabetics in this study. The study of Iacobellis et al.19
showed that elevated serum ALT level was associated with increased fasting
insulin and not with obesity per se. They suggested that the presence of
insulin resistance, rather than BMI alone, plays a role in mediating the
increased aminotransferase levels.19,20
We should emphasize that UNL calculated in
this study is the 95th percentile for serum ALT level in the studied
population and does not appropriately set the healthy serum ALT level which may
predict the over all mortality. Lack of measurement of serum triglyceride,
cholesterol, and fasting glucose, which influence on serum ALT level is the
limitation of this study.
The previous studies in Iran, Korea, and
Jordan have shown that the prevalence of diagnosed diabetes mellitus in adult
population was about 4% and if screening with fasting plasma glucose was used,
the prevalence would be increased to 7%.28–30 Although screening
with fasting plasma glucose was not performed in our study, the prevalence of
diagnosed diabetes mellitus was 4%, which is comparable with the previous
studies mentioned above.
In conclusion, considering the lower
calculated UNL in normal-weight, nondiabetic participants in this study, we
recommend setting new UNL for serum ALT level. The new threshold for serum ALT
level increases the sensitivity of the test for early diagnosis and follow-up
of patients with liver diseases. It seems reasonable to set UNL for serum ALT
level in males and females separately. However, considering the BMI for redefinition
of the UNL is not recommended because elevated levels in overweights may be a
clue to the diagnosis of NAFLD. Therefore, adjusting the UNL for overweights
will result in underdiagnosis of some patients with NAFLD.
Acknowledgment
This study was supported by research
funds of Tehran University of Medical Sciences, Digestive Disease Research Center (DDRC), and Iranian Blood Transfusion Organization (IBTO). The authors would
also extend their gratitude to Dr. Afshin Aslani, and Ms. Goharshad Googlani from
DDRC for their special help and support of this study and Ms. S. Raman, B. Amoo-Hossein,
M. Moghtadaie, R. Shamriz, and M. Mirzaie from IBTO for their technical
assistance.
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