Liver stiffness values in apparently healthy subjects: Influence of gender and metabolic syndrome

Liver stiffness values in apparently healthy subjects: Influence of gender and metabolic syndrome

Journal of Hepatology 48 (2008) 606–613 www.elsevier.com/locate/jhep Liver stiffness values in apparently healthy subjects: Influence of gender and met...

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Journal of Hepatology 48 (2008) 606–613 www.elsevier.com/locate/jhep

Liver stiffness values in apparently healthy subjects: Influence of gender and metabolic syndromeq Dominique Roulot1,2,3,*, Se´bastien Czernichow4,5, Herve´ Le Cle´siau6, Jean-Luc Costes6, Anne-Claire Vergnaud4, Michel Beaugrand3 1

Unite´ d’He´patologie, Hopital Avicenne, Assistance Publique, Hoˆpitaux de Paris, Bobigny, France 2 UPRES-EA 3406, Universite´ Paris 13, Bobigny, France 3 Service d’he´patogastroenterologie, Hoˆpital Jean Verdier, Assistance Publique, Hoˆpitaux de Paris, Bondy, France 4 INSERM, U55; INRA, U1125; CNAM, EA3200; CRNH-IdF, Universite´ Paris 13, Bobigny, France 5 De´partement de Sante´ Publique, Hoˆpital Avicenne, Assistance Publique, Hoˆpitaux de Paris, Bobigny, France 6 Centre d’examens de Sante´ de l’Assurance Maladie, Bobigny, France

See Editorial, pages 529–531

Background/Aims: Liver stiffness measurement by transient elastography is a very promising non-invasive method for the diagnosis of fibrosis in chronic liver diseases. However, studies on normal values of liver stiffness in healthy subjects are still lacking. The aim of the present study was to prospectively assess liver stiffness values in the general population and to determine potential factors, which may influence these values. Methods: Liver stiffness measurements were performed in 429 consecutive apparently healthy subjects, without overt cause of liver disease and normal liver enzymes, undergoing a free medical check-up. Results: Mean liver stiffness value was 5.49 ± 1.59 kPa. Transient elastography failure was observed in 4.6% of the cases. The failure rate increased with BMI, reaching 88% for values above 40 kg /m2. Liver stiffness values were higher in men than in women (5.81 ± 1.54 vs 5.23 ± 1.59 kPa, p = 0.0002) and in subjects with BMI > 30 kg/m2 (6.26 ± 1.89 vs 5.37 ± 1.51 kPa, p = 0.0003). Metabolic syndrome was diagnosed in 59 (13.7%) subjects. After adjustment for gender and BMI, liver stiffness values were higher in subjects with metabolic syndrome than in those without (6.51 ± 1.64 vs 5.33 ± 1.51 kPa, p < 0.0001). Conclusions: Liver stiffness values in the general population are influenced independently by gender, BMI and metabolic syndrome.  2007 European Association for the Study of the Liver. Published by Elsevier B.V. All rights reserved. Keywords: Transient elastography; Fibroscan; Liver stiffness; Metabolic syndrome; Healthy subjects; Gender; BMI

Received 27 June 2007; received in revised form 27 October 2007; accepted 8 November 2007; available online 3 January 2008 Associate Editor: C.P. Day q The authors who have taken part in the research of this paper declared that they do not have a relationship with the manufacturers of the device involved either in the past or present and they did not receive funding from the manufacturers to carry out their research. They did not receive funding from any source to carry out this study. * Corresponding author. Tel.: +33 1 48 95 54 30; fax: +33 1 48 95 54 50. E-mail address: [email protected] (D. Roulot). Abbreviations: ALT, alanine aminotransferase; AST, aspartate aminotransferase; BMI, body-mass index; GGT, gamma-glutamyl-transpeptidase; HCV, hepatitis C virus; HDL, high-density lipoprotein; LDL, low-density lipoprotein; NASH, non-alcoholic steatohepatitis; TE, transient elastography. 0168-8278/$34.00  2007 European Association for the Study of the Liver. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.jhep.2007.11.020

D. Roulot et al. / Journal of Hepatology 48 (2008) 606–613

1. Introduction Transient elastography (TE) is a recently described non-invasive procedure, which measures the transmission of a mechanical wave generated by vibration. This technique allows to evaluate liver stiffness [1]. A strong correlation between liver stiffness measurements and liver fibrosis stages, assessed by simultaneous liver biopsies, has initially been reported in chronic hepatitis C [2,3]. More recently, a similar correlation has been demonstrated in other chronic liver diseases including non-alcoholic steatohepatitis (NASH) [4]. TE allows the accurate prediction of cirrhosis and of its complications in patients with chronic liver disease [5]. The high reproducibility of liver stiffness measurement has recently been reported [6], together with a low rate of failure, mostly observed in overweight subjects [7]. Accordingly, in HCV patients TE success rate was lower in obese than non-obese patients and decreased with age [8]. Because TE is simple to perform, user-friendly, totally innocuous and reproducible, this procedure will probably gain popularity for the diagnosis and followup of liver diseases. However, an important prerequisite for the widespread application of TE in clinical practice is the establishment of normal values in large series of healthy subjects. Moreover, as liver fibrosis may occur in subjects with chronic hepatic disease despite of persistently normal liver enzymes, TE could be used for the screening of liver involvement in the general population. In the present study, we investigated liver stiffness values in a series of 429 healthy subjects without overt liver disease and normal liver enzymes. We studied potential factors influencing liver stiffness measures, including age, gender, body-mass index (BMI) and metabolic syndrome.

2. Patients and methods 2.1. Patients All subjects undergoing a systematic free medical check-up in a Social Medical Center (Bobigny, France) between September 2005 and June 2006 were eligible. All subjects gave written and informed consent, and the study protocol was approved by the local ethics committee (CCPPRB, Aulnay-sous-bois, France). Subjects underwent liver stiffness measurements and had a complete medical examination with laboratory tests on the same day. The following data were collected for each subject: age, gender, daily alcohol intake (number of glasses of alcohol per week) or previous history of excessive alcohol consumption (>30 g per day), tobacco use, history of arterial hypertension, diabetes or dyslipidemia, type and duration of antidiabetic and antihypertensive treatments, BMI, waist circumference, systolic and diastolic blood pressure. Laboratory tests included: platelet count and mean globular volume, gamma-glutamyl transferase (GGT), aspartate aminotransferase (AST), alanine transferase (ALT), total HDL and LDL cholesterol, triglycerides, fasting glucose, ferritin; serological tests for hepatitis B surface antigen (Hbs Ag), hepatitis C virus (anti-HCV) antibodies.

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According to the National Cholesterol Education Program (NCEP) criteria [9], metabolic syndrome was diagnosed in subjects displaying at least three of the five following features: (1) waist circumference >102 cm in men and >88 cm in women; (2) triglycerides P150 mg/dl (1.69 mmol/l); (3) HDL cholesterol <40 mg/dl (1.04 mmol/l) in men and <50 mg/dl (1.29 mmol/l) in women; (4) blood pressure P130/85 mmHg; (5) fasting glucose P110 mg/dl (6.1 mmol/l). Participants under antidiabetic (oral agents or insulin) or antihypertensive medication were classified for the study as subjects having increased fasting blood glucose or increased blood pressure, respectively.

2.2. Liver stiffness measurements TE (FibroScan, Echosens, Paris, France) was performed in all subjects by the same physician blinded to clinical and biological data. Details of the technical description and examination procedure have been described previously [1]. Briefly, an ultrasound transducer probe is mounted on the axis of a vibrator. Vibrations of mild amplitude (1 mm) and low frequency (50 Hz) are transmitted by the transducer, inducing an elastic shear wave that propagates through underlying tissues. Pulse-echo ultrasound acquisitions are used to follow the propagation of the shear wave and to measure its velocity, which is directly related to tissue stiffness (the elastic modulus): the stiffer the tissue, the faster the shear wave propagates. TE measures liver stiffness in a volume that approximates a cylinder of 1 cm wide and 4 cm long, 25– 65 mm below the skin surface. This volume is at least 100 times larger than that of a biopsy sample and is therefore far more representative of the hepatic parenchyma. The success rate of liver stiffness measurements was calculated as the ratio between validated and total measurements. Results were expressed as the median value of the total measurements in kilopascals (kPa), values ranging from 2.5 to 75 kPa [2]. Only procedures with at least ten successful acquisitions and a success rate of at least 60% were considered reliable. In addition, the median value of successful measurements was considered representative of the liver stiffness in a given patient, only if the interquartile (IQR) range of all validated measurements was less than 30% of the median value.

2.3. Statistical analysis Results were expressed as means ± standard deviations (SD) or percentages. Variables with skewed distributions were log-transformed and geometric means, as well as 95% confidence intervals (95% CI) are presented. Spearman coefficient correlations were computed between liver stiffness measurements and all continuous variables. Characteristics of all subjects, of subjects according to gender, and of subjects according to the metabolic syndrome status were compared by Student’s t-test and Chi-square test where appropriate. Using analysis of covariance we compared liver stiffness measurements means between subjects with metabolic syndrome and those without. Multivariate models were adjusted for age, gender, BMI, transaminases, GGT and ferritin levels. All statistical analyses were carried out with standard procedures (SAS, version 8.02). Statistical significance was judged at a < 0.05.

3. Results 3.1. Subject selection A total of 683 subjects were enrolled in the study. Seventy-nine of them (11.6%) were excluded because of missing clinical or biological data (Fig. 1). These subjects did not differ from the selected subjects for age (44.2 vs 45.1 yrs, respectively; NS), gender (women: 51.9% vs 54.3%, respectively; NS) and BMI (25.2 vs 25.6 kg/m2, NS). Thirty-two subjects (4.6%) were

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in women but no influence on liver stiffness could be found by multivariate analysis. 3.2. Influence of age, gender and BMI on liver stiffness measurements

Fig. 1. Flow chart of the study. After exclusion of subjects with unreliable liver stiffness measurements, missing data, or suspicion of chronic liver disease, 429 subjects were included in the study. In 59 of them a previously unknown metabolic syndrome was diagnosed.

excluded because of unreliable liver stiffness measurement, with fewer than ten successful acquisitions, or a success rate of liver stiffness measurement below 60% (see Section 2). The failure rate of liver stiffness measurements increased with BMI: 0.9% for BMI < 25 kg/m2; 4.6% for BMI between 25 kg/m2 and 30 kg/m2; 25% for BMI between 30 kg/m2 and 35 kg/m2; 41% for BMI > 35 kg/m2; 88% for a BMI > 40 kg/m2. Of the 572 remaining subjects, only subjects with normal liver enzymes and without overt cause of liver disease were considered for subsequent analysis. An additional 143 subjects were excluded because of past or present excessive alcohol consumption (n = 13) and/ or HCV or HBV positive tests (n = 19), and/or biological abnormalities (n = 124), defined as GGT >45 UI/L (n = 85), transaminases >40 UI/L (n = 53), ferritin >350 lg/L (n = 35), mean globular volume >98 lm3 (n = 14) and platelets <150 · 103/mm3 (n = 8). Finally, a total of 429 subjects were analyzed. Their characteristics are shown in Table 1. Among these 429 subjects, the percentage of women was higher than that of men (54.3 vs 45.7%), reflecting the distribution within the general population. The mean age according to the gender was comparable (44.2 ± 16.5 vs 46.2 ± 16.9 yrs, for women and men, respectively, p = 0.22). The mean BMI was 25.8 ± 4.6 kg/m2 for women and 25.6 ± 3.7 kg/m2 for men. Fifty-nine (13.7%) subjects displayed metabolic syndrome (Fig. 1). Subjects were also classified, as a function of their tobacco use, in no smokers, past smokers and current smokers (Tables 1 and 3). Tobacco use was significantly higher in men than

Mean liver stiffness value of the 429 subjects was 5.49 ± 1.59 kPa. Liver stiffness values tended to be higher with age, although the difference did not reach statistical significance (p = 0.06) (Fig. 2). Liver stiffness values were significantly higher in men than in women (5.81 ± 1.54 vs 5.23 ± 1.59 kPa, respectively, p = 0.0002) (Fig. 3). Because a different percentage of obesity (BMI > 30 kg/m2) was observed in men than women (18.9 vs 9.2%, respectively, p < 0.004), we next examined whether BMI could affect liver stiffness values. Liver stiffness was found to be significantly higher in subjects with BMI >30 kg/m2 than in overweight or normal subjects, after adjusting for age, sex, ALT, AST and ferritin (p = 0.0005) (Table 2). 3.3. Influence of metabolic syndrome on liver stiffness values Metabolic syndrome was diagnosed in 59 subjects. Characteristics of subjects according to the presence or absence of metabolic syndrome are summarized in Table 3. Gender distribution was similar in the metabolic syndrome group and the normal group (women corresponding to 50.8% and 54.9%, respectively, p = 0.56). The mean age was significantly higher in the metabolic syndrome group than in the normal group (56.3 ± 13.3 vs 43.3 ± 16.5 yrs, respectively, p < 0.0001). As expected, BMI values above 30 kg/m2 were more frequent among subjects with metabolic syndrome than in normal subjects (49.1% vs 8.9%, respectively, p < 0.0001). Mean liver stiffness value was higher in subjects with metabolic syndrome compared to controls: 6.51 ± 1.64 vs 5.33 ± 1.51 kPa, (p < 0.0001) (Fig. 4). In multivariate analysis, the differences of liver stiffness values were still significant between the two groups (with and without metabolic syndrome): the metabolic syndrome appears to be the most important factor associated with liver stiffness independently of BMI and other covariates (p = 0.0002, Table 4). For most individuals with high liver stiffness values, liver biopsy was not justified because of normal liver enzymes. However, in seven patients with metabolic syndrome and liver stiffness values above 8.0 kPa, histological examination of the liver was proposed, because previous studies had reported that threshold values of liver stiffness predictive for significant liver fibrosis (i.e. Metavir F score P 2), ranged from 7 and 8.8 kPa [2,3,6]. In the four patients who accepted liver biopsy, anatomical lesions of NASH were present with a F2

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Table 1 Main characteristics of the 429 evaluated subjects

Number (%) Age (years) Tobacco use (%) No smokers Past smokers Current smokers Alcohol consumption (glass/week)b BMI (kg/m2) <30 kg/m2 (n = 367) (%) P30 kg/m2(n = 62) (%) Waist circumference (cm) SBP (mmHg) DBP (mmHg) Fasting blood glucose (mmol/l)a GGT (Ul/l)a,c Triglycerides (mmol/l)a Total cholesterol (mmol/l) HDL cholesterol(mmol/l) LDL cholesterol (mmol/l) Ferritin (lg/l)a ALT (Ul/l)c AST (Ul/l)c Liver stiffness (kPa) [min–max] 95th percentile Subjects without MS and with BMI < 30 kg/m2 number Liver stiffness (kPa)

All subjects

Men

Women

429 45.1 ± 16.7

196 (45.7) 46.2 ± 16.9

233 (54.3) 44.2 ± 16.5

67.52 14.72 17.76 1.42 ± 2.45 25.6 ± 4.2 85.55 14.45 85.8 ± 12.1 126.1 ± 13.2 75.3 ± 8.3 5.16 [5.07–5.25] 16.1 [15.5–16.8] 0.92 [0.88–0.97] 4.97 ± 1.00 1.40 ± 0.35 3.09 ± 0.83 60.0 [54.3–66.3] 18.0 ± 6.6 19.6 ± 4.2 5.49 ± 1.59 [1.5–12.7] 8.6 337 5.30 ± 1.45

56.12 24.49 19.39 1.94 ± 2.90 25.4 ± 3.7 90.8 9.2 89.4 ± 11.1 129.5 ± 11.9 77.0 ± 7.3 5.34 [5.19–5.50] 18.4 [17.3–19.6] 1.02 [0.95–1.09] 4.98 ± 0.92 1.29 ± 0.30 3.17 ± 0.78 104.8 [94–116.6] 20.2 ± 6.7 20.6 ± 4.1 5.81 ± 1.54 [3.3–12.7] 9.0 159 5.60 ± 1.30

77.16 6.47 16.38 0.99 ± 1.88 25.8 ± 4.6 81.1 18.9 82.8 ± 12.1 123.3 ± 13.6 73.7 ± 8.7 5.01 [4.91–5.12] 14.4 [13.7–15.2] 0.85 [0.80–0.91] 4.96 ± 1.07 1.49 ± 0.37 3.03 ± 0.87 37.6 [32.9–43.0] 16.2 ± 5.8 18.8 ± 4.1 5.23 ± 1.59 [1.5–11.3] 7.9 178 5.05 ± 1.49

p 0.2205 <.0001

0.0012 0.3483 0.0044 <.0001 <.0001 <.0001 0.0005 <.0001 0.0004 0.8582 <.0001 0.0681 <.0001 <.0001 <.0001 0.0002

0.0006

Means ± SD and %. p values are performed with test for continuous variables and Chi-square test for qualitative variables. BMI, body-mass index; SBP, systolic blood pressure; DBP, diastolic blood pressure; GGT, gamma-glutamyl-transpeptidase; HDL, high-density lipoprotein; LDL, low-density lipoprotein; ALT, alanine aminotransferase; AST, aspartate aminotransferase, MS, metabolic syndrome. a Geometric means and 95% CI are performed because of skewed distribution. b Test on ranks. c Normal values. GGT < 45 UI/l; AST < 40 UI/l; ALT < 40 UI/l.

score of portal fibrosis and liver steatosis involving less than 10% of the hepatocytes, according to the grading system for steatohepatitis [10]. From the results of our study, it is difficult to define normal values of liver stiffness in the general population. However, based on the calculation of the 95th percentile, we can conclude that 90% of a normal non-obese

population, without metabolic syndrome, displays liver stiffness values comprised between 3.3 and 7.8 kPa (5.05 ± 1.49, means ± SD) in women and between 3.8 and 8.0 kPa (5.60 ± 1.30, means ± SD) in men.

Fig. 2. Correlation between liver stiffness and the age of the subjects.

Fig. 3. Distribution of liver stiffness values according to gender.

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Table 2 Association between liver stiffness values and BMI

n (subjects) M1 M2

BMI < 25

25 6 BMI < 30

BMI P 30

p

204 5.41 ± 0.11 5.44 ± 0.11

163 5.37 ± 0.12 5.33 ± 0.12

62 6.26 ± 0.20 6.23 ± 0.20

0.0003 0.0005

M1: age, sex-adjusted. M2: age, sex, ALT, AST and ferritin-adjusted. BMI, body-mass index (kg/m2); ALT, alanine aminotransferase; AST, aspartate aminotransferase.

4. Discussion Despite the increasing popularity of TE to explore liver diseases, liver stiffness values had not been determined in large populations of apparently healthy subjects and normal values were still lacking. We studied 429 consecutive subjects undergoing systematic checkup in a social medical center, who were carefully selected for absence of obvious hepatic risk factors and clinical and biological evidence of liver disease. The investigated subjects have been selected from an initial group of 683 participants, in which the percentage of individuals with positive HbsAg or anti-HCV antibodies (2.7%, n = 19)

Fig. 4. Distribution of liver stiffness values according to the presence or absence of metabolic syndrome.

is representative of the national French population. Reported alcohol consumption was below the national average, probably because it was under-estimated in the questionnaire filled by the participants. 47.6% of

Table 3 Subject characteristics according to metabolic syndrome (MS) statusa

n = 429 Women (%) Age (years) Tobacco use (%) No smokers Past smokers Current smokers Alcohol consumption (glass/week)c BMI (kg/m2) <30 kg/m2 (%) P30 kg/m2 (%) Waist circumference (cm) SBP (mmHg) DBP (mmHg) Fasting blood glucose (mmol/l)b GGT (Ul/l)b Triglycerides (mmol/l)b Total cholesterol (mmol/l) HDL (mmol/l) LDL (mmol/l) Ferritin (lg/l)b ALT (Ul/l) AST (Ul/l) Liver stiffness (kPa) all subjects Liver stiffness (kPa) if BMI < 30 kg/m2

No MS

MS

370 54.9 43.3 ± 16.5

59 50.8 56.3 ± 13.3

67.84 14.05 18.11 1.46 ± 2.32 24.9 ± 3.8 91.1 8.9 83.6 ± 10.9 124.7 ± 12.8 74.6 ± 8.3 4.96 [4.91–5.01] 15.7 [15.0–16.4] 0.84 [0.80–0.88] 4.92 ± 1.00 1.44 ± 0.35 3.05 ± 0.82 57.9 [52.1–64.5] 17.6 ± 6.5 19.7 ± 4.2 5.33 ± 1.51 5.30 ± 1.45

65.52 18.97 15.52 1.22 ± 3.13 30.0 ± 4.0 50.8 49.1 99.4 ± 10.2 135.0 ± 12.2 79.2 ± 7.1 6.63 [6.10–7.22] 18.8 [16.9–20.9] 1.64 [1.47–1.84] 5.28 ± 0.99 1.13 ± 0.22 3.34 ± 0.86 74.9 [57.0–98.3] 20.1 ± 6.7 18.8 ± 4.4 6.51 ± 1.64 6.25 ± 1.96

p 0.5651 <.0001 0.5912

0.0174 <.0001 <.0001 <.0001 <.0001 <.0001 <.0001 0.0034 <.0001 0.0098 <.0001 0.0149 0.0835 0.0064 0.1316 <.0001 0.0106

p values are performed with t-test for continuous variables and Chi-square test for qualitative variables. BMI, body-mass index; SBP, systolic blood pressure; DBP, diastolic blood pressure; GGT, gamma-glutamyl-transpeptidase; HDL, high-density lipoprotein; LDL, low-density lipoprotein; ALT, alanine aminotransferase; AST, aspartate aminotransferase. a Means ± SD and %. b Geometric means and 95% CI are performed because of skewed distribution. c Test on ranks.

D. Roulot et al. / Journal of Hepatology 48 (2008) 606–613 Table 4 Association between liver stiffness and metabolic syndrome (MS) status No MS n (subjects) 370 Liver stiffness (kPa) Crude 5.33 ± 0.08 M1 5.36 ± 0.08 M2 5.36 ± 0.08

MS

p

59 6.51 ± 0.20 6.48 ± 0.20 6.46 ± 0.22

<.0001 <.0001 <.0001

M1: age, sex-adjusted. M2: age, sex, BMI, ALT, AST, GGT and ferritin-adjusted (means ± SE). BMI, body-mass index; ALT,alanine aminotransferase; AST, aspartate aminotransferase GGT, gamma-glutamyl-transpeptidase.

the studied subjects showed a normal BMI, whereas 37.9% were overweight and 14.4% obese. The prevalence of obesity in this study-group is high for a French population-based study. However, this increased rate is explained by the low socio-economic status of the subjects living in the district where the study was conducted [11]. As reported previously, reliable liver stiffness measurements can be difficult to obtain in obese patients. In our study, the proportion of patients in whom liver stiffness measurements could not be obtained (4.6%) is close to that of 5% reported in another prospective study of 2114 cases [7]. In that study, multivariate analysis showed that the only factor associated with liver stiffness measurement failure was a body-mass index above 28 kg/m2. All but two subjects of the present study with unreliable liver stiffness values (n = 32) had a BMI above 28 kg/m2 (values ranging from 28 to 45 kg/m2). Overall, we found that liver stiffness measurements are almost impossible to obtain for BMI > 40 (88% of failure rate). An important finding of the present study is that liver stiffness is significantly influenced by gender, with higher values found in men than in women. This finding, which is consistent with the results of a previous study conducted on a small population of supposedly ‘‘healthy subjects’’ [12], indicates that gender should be taken into account when interpreting liver stiffness values. It also suggests the existence of intrinsic differences between men and women in the density of liver extracellular matrix [13], a hypothesis supported by previous studies showing that ovarian hormones inhibit extracellular matrix production by liver stellate cells [14]. Another interesting finding of our study is that mean liver stiffness values were significantly higher in subjects in whom a metabolic syndrome was diagnosed, compared to other subjects. In multivariate analysis, the metabolic syndrome appeared to be the most important factor associated with liver stiffness, independently of BMI. Metabolic syndrome is frequent, affecting 10% 25% of the general population in western countries [15]. The percentage of subjects with metabolic syn-

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drome among the 429 individuals of our study was 13.7%, close to the value of 11% found in the French DESIR study [16]. Clinical, epidemiological and biochemical data strongly support the concept that nonalcoholic fatty liver disease (NAFLD) is the hepatic manifestation of the metabolic syndrome [17]. NAFLD has been recently recognized as a leading cause of chronic liver disease in the Western world with an estimated prevalence up to 30% [18–20]. A significant proportion of patients with NAFLD can progress to cirrhosis, liver failure and, possibly, hepatocellular carcinoma [21–24]. However, no factors have been recognized that determine increasing fibrosis and histologically advanced disease during NAFLD. In addition, advanced hepatic disease may be present in individuals with normal aminotransferase levels and normal ultrasound examination [25–28]. Ultrasonography may misdiagnose non-alcoholic fatty liver disease in 10–30% of the cases and cannot distinguish steatohepatitis from simple steatosis. Liver biopsy remains the gold standard for the assessment of fibrosis in patients with chronic liver disease. However, in case of suspicion of NAFLD, liver biopsy is difficult to recommend for apparently healthy patients with normal aminotransferases, because of potential, albeit infrequent, associated risks. In addition, histological lesions of NASH are unevenly distributed throughout the liver parenchyma and sampling error of liver biopsy, resulting in substantial misdiagnosis and staging inaccuracies, are frequent in this disease [29]. These limitations have led to the development of new non-invasive parameters to assess fibrosis, such as biochemical surrogate markers of fibrosis [30–32] or the FibroTest, a panel of biological markers reported to predict advanced fibrosis [33]. Combination of multiple biological markers and clinical data were also proposed to predict liver fibrosis in patients with NAFLD [34–36]. At present it is difficult to determine the real impact of TE in the early diagnosis of liver involvement in patients with metabolic syndrome. In our study, among the 30 subjects with metabolic syndrome and BMI < 30 K/m2, seven displayed high TE values above 8 kPa. Interestingly, in the four subjects belonging to this group who underwent liver biopsy, the histological examination revealed portal fibrosis with minor or absent steatosis. These data support the hypothesis that isolated steatosis does not increase liver stiffness, in agreement with previous studies, performed in the context of chronic hepatitis C, indicating that the correlation between liver stiffness and the fibrosis stage was not influenced by steatosis or activity grade [3,37]. In most (88%) of our subjects with metabolic syndrome, however, TE values fell within the ‘‘normal range’’ of the non-metabolic syndrome group, limiting the discriminatory value of the test in this context. Future investigation will determine whether or not the

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individual follow-up of TE values in patients with metabolic syndrome may predict the evolution toward liver fibrosis. In conclusion, we have determined liver stiffness values in a large group of presumably healthy subjects. Although the differences observed are relatively small, given the spread of data in the examined groups, we could determine that liver stiffness was significantly higher in men than in women. In addition, previously undiagnosed metabolic syndrome was positively associated with enhanced values of liver stiffness in subjects with normal liver enzymes levels and no overt liver disease, independently of their BMI. Acknowledgments The Fibroscan device was made available for the study by Echosens (Paris, France). We thank Ce´line Fournier who assisted us in setting up TE in the social medical center. References [1] Sandrin L, Fourquet B, Hasquenoph JM, Yon S, Fournier C, Mal F, et al. Transient elastography: a new noninvasive method for assessment of hepatic fibrosis. Ultrasound Med Biol 2003;29:1705–1713. [2] Castera L, Vergniol J, Foucher J, Le Bail B, Chanteloup E, Haaser M, et al. Prospective comparison of transient elastography, Fibrotest, APRI, and liver biopsy for the assessment of fibrosis in chronic hepatitis C. Gastroenterology 2005;128:343–350. [3] Ziol M, Handra-Luca A, Kettaneh A, Christidis C, Mal F, Kazemi F, et al. Noninvasive assessment of liver fibrosis by measurement of stiffness in patients with chronic hepatitis C. Hepatology 2005;41:48–54. [4] de Ledinghen V, Beaugrand M, Kelleher TB, Foucher J, Castera L, Ziol M, et al. Prediction of liver fibrosis in non-alcoholic steatohepatitis (NASH): risk factors and diagnostic potential of liver elasticity using Fibroscan. J Hepatol 2006;44:S39. [5] Kazemi F, Kettaneh A, N’Kontchou G, Pinto E, Ganne-Carrie N, Trinchet JC, et al. Liver stiffness measurement selects patients with cirrhosis at risk of bearing large oesophageal varices. J Hepatol 2006;45:230–235. [6] Fraquelli M, Rigamonti C, Casazza G, Conte D, Donato MF, Ronchi G, et al. Reproducibility of transient elastography in the evaluation of liver fibrosis in patients with chronic liver disease. Gut 2007;56:968–973. [7] Foucher J, Castera L, Bernard PH, Adhoute X, Laharie D, Bertet J, et al. Prevalence and factors associated with failure of liver stiffness measurement using FibroScan in a prospective study of 2114 examinations. Eur J Gastroenterol Hepatol 2006;18:411–412. [8] Kettaneh A, Marcellin P, Douvin C, Poupon R, Ziol M, Beaugrand M, et al. Features associated with success rate and performance of fibroscan measurements for the diagnosis of cirrhosis in HCV patients: a prospective study of 935 patients. J Hepatol 2007;46:628–634. [9] Executive Summary of The Third Report of The National Cholesterol Education Program (NCEP) Expert Panel on Detection, Evaluation, And Treatment of High Blood Cholesterol In Adults (Adult Treatment Panel III). JAMA 2001;285:2486–2497.

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