Elevated serum alanine transaminase in patients with type 1 or type 2 diabetes mellitus
From the 1Division of Epidemiology & Public Health, 2Wolfson Digestive Diseases Centre and 4Department of Biomedical Sciences, University of Nottingham Medical School, 3Divisions of Diabetes & Endocrinology and Queen's Medical Centre, Nottingham, UK
Address correspondence to Dr G.P. Aithal, Consultant Hepatobiliary Physician, D Floor, South Block, Queen's Medical Centre University Hospital, Nottingham NG7 2UH, UK. email: guru.aithal{at}qmc.nhs.uk
Received 25 April 2006 and in revised form 3 July 2006
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Background: The risk of chronic liver disease is higher in diabetics, and serum alanine transaminase (ALT) is a sensitive predictor of mortality from liver disease.
Aim: To estimate the prevalence of elevated ALT in type 1 and type 2 diabetes, and identify possible risk factors.
Methods: We identified all patients (n = 2077) attending review between September 2002 and August 2003. We excluded those with no ALT measurement (n = 73); those whose alcohol consumption was >14 units/week (women) (n = 276) or >21 units/week (men) (n = 324); and those with a diagnosis of Maturity Onset Diabetes of the Young, secondary diabetes, gestational diabetes or uncertain type of diabetes (n = 51). We calculated the prevalences of elevated ALT in both type 1 and type 2 diabetes patients, and compared the demographic, microvascular risk factors and current drug use between each group using multivariate logistic regression.
Results: Of 1353 patients included, 836 (61.9%) had type 2 diabetes. Elevated ALT was found in 9.5% (95%CI 7.1–12.3%) of patients with type 1 diabetes, and 12.1% (95%CI 9.9–14.5%) of those with type 2 diabetes. The risk of elevated ALT in patients with type 2 diabetes increased with increasing body mass index (ptrend = 0.04), and was lower in those taking insulin (OR 0.38, 95%CI 0.22–0.65).
Discussion: The prevalence of elevated ALT is 3–4 times higher in patients with either type 1 or type 2 diabetes than in the general population. Further studies investigating the aetiology and mechanisms of this elevation may suggest appropriate early interventions.
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Introduction |
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Diabetes mellitus (DM) is associated with non-alcoholic fatty liver disease (NAFLD) including its severe form, non-alcoholic steatohepatitis (NASH).1,2 Among patients with diabetes, the risk of chronic liver disease is doubled, independent of alcoholic liver disease or viral hepatitis.3 Diabetes also increases the risk of primary liver cancers3–5 and death from liver cirrhosis.6,7 However, the prevalence of previously undetected liver disease in a large unselected diabetic population has not been examined.7
Alanine transaminase (ALT) is a widely available serum marker of liver disease. Even a minor elevation of ALT is a good predictor of mortality from liver disease.8 In previous reports, including one from our centre, NAFLD was the most common diagnosis, accounting for 64–90% of cases, when detailed investigations were carried out in patients with asymptomatic elevated liver enzymes.9–11 In a large population-based study analysing data from the Third National Health and Nutrition Examination Survey (NHANES III), ALT elevation was associated with a number of risk factors of NAFLD, such as impaired glucose metabolism, insulin resistance, central obesity, high leptin and triglycerides, even when patients with known diabetes (who are at high risk for NAFLD) were excluded.12 Hence, raised ALT has been used as a marker of NAFLD in epidemiological studies.13 In the current study, we have estimated the prevalence of and risk factors for elevated ALT in both Type 1 and Type 2 diabetes.
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Methods |
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Queen's Medical Centre serves a population of about 350 000. Of prevalent cases, about 15% of type 2 and 95% of type 1 diabetes attend hospital diabetes services at any one time. From our Diabetic Registry, we identified all those who attended for review between September 2002 and August 2003.
Data collected prospectively included age, gender, type of diabetes, height, weight, blood pressure, self-reported alcohol intake at the time of registration on the database (and updated during clinical practice), microvascular risk factors and current medications. During the study period, the routine laboratory measurements included: urea and electrolytes; HbA1c; lipid profile and liver profile (including ALT, 
-glutamyl transferase, alkaline phosphatase, bilirubin and albumin). ALT was estimated using Vitros dry-slide analysis (Johnson & Johnson, Ortho Clinical Diagnostics).
Hypertension was defined as either current use of anti-hypertensive medication or blood pressure >140/80 mmHg. Microalbuminuria was defined as either dipstick positive for protein or albumin/creatinine ratio (in mg/mmol) of >2.5 for women or >3.5 for men. Dyslipidaemia was defined as at least one of: current use of lipid-lowering medication; serum cholesterol >5 mmol/l; LDL >3 mmol/l; triglyceride >2.3 mmol/l; HDL <1 mmol/l.14 We categorized body mass index (BMI) into standard categories, current age into 10-year age bands, and HbA1c into quartiles. We defined elevated ALT as >50 IU/l.
Statistical analyses
We calculated the prevalence and 95%CIs of elevated ALT in both type 1 and type 2 diabetes, and compared the demographic, microvascular risk factors and current drug use between each group. To assess the risk factors for elevated ALT, we used multivariable logistic regression modelling, including all covariates. In the multivariate analyses, we only included those people with no missing values. To examine linear trends, we fitted categorical variables as quantitative variables and assessed goodness-of-fit of the nested models using likelihood ratio tests. All analyses used Stata 7.0/SE.
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Results |
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We identified 2077 people (of 2999 on the database at the time of the study) who attended for review during the 1-year study period. We excluded those who did not have ALT measured (n = 73), those whose alcohol consumption exceeded 14 units/week for women (n = 276) or 21 units/week for men (n = 324), and those with a diagnosis of Maturity Onset Diabetes of the Young, secondary diabetes, gestational diabetes or uncertain type of diabetes (n = 51). Of the 1353 patients included, 836 (61.9%) had type 2 diabetes. Elevated ALT was found in 9.5% (95%CI 7.1–12.3%) of those with type 1 diabetes and 12.1% (95%CI 9.9–14.5%) of those with type 2 diabetes.
Table 1 shows the characteristics of the included subjects by ALT category, and the unadjusted risk estimates for association with each characteristic. There were missing values in only the body mass index and HbA1c variables.
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Table 2 shows the multivariable analyses of the risk of elevated ALT from various characteristics. The prevalence of elevated ALT decreased with increasing age in type 2 diabetes (although not statistically significant at the 5% level). In type 2 diabetes, the risk of elevated ALT increased with increasing BMI category (>30 vs.
25, OR 2.76, 95%CI 0.91–8.38, ptrend = 0.04) and decreased with current treatment with insulin (OR 0.38, 95%CI 0.22–0.65).
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Discussion |
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The prevalences of elevated ALT in our type 1 (9.5%) and type 2 (12.1%) diabetes patients were both considerably higher than the 2.7% expected in the general population,8 and higher than 5.6% reported at baseline in clinical trials.15 This suggests that about 10% of diabetes patients under regular review in secondary care may need further investigation for the causes of raised ALT, and has potential resource implications. However, these prevalences of raised ALT may still be underestimates, for two reasons. Firstly, a single estimation of ALT was used to define abnormality. Fluctuation in the ALT levels is recognized in patients with chronic liver disease, and a single measurement can underestimate disease burden.13 Secondly, we defined ALT >50 U/l as abnormal, according to our laboratory range, which was established from 2 SD of ALT estimations in apparently healthy subjects. This concept of establishing normal ranges for ALT based on apparently healthy subjects has been challenged; recent studies have argued that cut-off values identified using normograms of ALT estimations in apparently normal subjects may miss occult chronic liver disease, and underestimate the population at risk of mortality from liver diseases.9 We acknowledge that our pragmatic approach to defining elevated ALT may have underestimated the prevalence of NAFLD slightly.
As the study included patients attending their hospital review, there is likely to be some selection bias. This may be particularly true of patients with type 2 diabetes, as only 15% of prevalent cases are under hospital review. A variety of factors, including referral pattern, co-morbidity and poor control, can influence the selection of patients for regular hospital review. Although we have controlled for this to some extent by including HbA1c in our multivariable analysis, findings of the current study may not be true of an unselected population of type 2 diabetes and will require confirmation in population-based studies. It is unlikely that selection bias would have affected the findings in type 1 diabetes as 95% of such patients are under regular hospital review.
Although we have not investigated patients with ALT elevation, high alcohol consumption is unlikely to be a major confounder, as we excluded those with moderate or excess alcohol intake. The prevalence of chronic viral hepatitis in our population is likely to be very low (<1–2%), and hence is unlikely to explain the high prevalence of abnormal ALT. Therefore, based on previous reports including that from our centre, we have assumed that the majority of these patients have NAFLD.9–11 Our finding that patients with type 2 diabetes had a higher risk of elevated ALT with increasing body mass index (ptrend = 0.04) is consistent with the well-established association of NAFLD with metabolic syndrome, and is supportive of our underlying assumption.
The spectrum of NAFLD, including its severe form NASH, has been consistently associated with insulin resistance and hyperinsulinaemia.16–18 This has raised a concern that treatment with insulin in type 2 diabetes may aggravate liver disease. Consistent with this, in data from de Marco et al.,6 the standardized mortality ratio from cirrhosis in patients with type 2 diabetes was higher in those treated with insulin (OR 6.8 vs. diet alone) than in those on oral hypoglycaemic agents (OR 4.9 vs. diet alone).6 However, both hyperglycaemia and hyperinsulinaemia can promote fatty infiltration of the liver. Long-standing type 2 diabetes may be associated with relative insulin deficiency, and appropriate insulin treatment would shift the balance against hepatic steatosis. Therefore, our observation that current insulin use in patients with type 2 diabetes is associated with a reduced risk of elevated ALT is reassuring, but requires confirmation in larger groups.
Previous reports of raised liver enzymes in patients with type 1 diabetes have been limited to small case series.19,20 In reports where patients with liver test abnormalities were investigated in detail, marked accumulation of glycogen and steatohepatitis were demonstrated on liver biopsy.19,20 We did not identify any statistically significant risk factors in type 1 diabetes, although elevated ALT was slightly more common in men, and appeared to show some association with microalbuminuria and dyslipidaemia. Risk factors for elevated liver enzymes in Type 1 diabetes should be investigated further in future studies.
In summary, the prevalence of elevated ALT is 3–4 times higher in patients with either type 1 or type 2 diabetes than in the general population. Further studies investigating the aetiology and mechanisms of this elevation may suggest appropriate early interventions.
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References |
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