Comparison of Transient Elastography and Liver Biopsy for the Assessment of Liver Fibrosis in HIV/Hepatitis C Virus-coinfected Patients and Correlation with Noninvasive Serum Markers

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Comparison of Transient Elastography and Liver Biopsy for the Assessment of Liver Fibrosis in HIV/Hepatitis C Virus-coinfected Patients and Correlation with Noninvasive Serum Markers

Abstract

Transient elastography (FibroScan®) is a novel, rapid and noninvasive technique to assess liver fibrosis. Our objective was to compare transient elastography (TE) and other noninvasive serum indexes as alternatives to liver biopsy in HIV/hepatitis C virus (HCV)-coinfected patients. The fibrosis stage (METAVIR Score), TE, the aspartate aminotransferase-to-platelet ratio index, the Forns fibrosis index, FIB-4 and HGM-2 indexes were assessed in 100 patients between January 2007 and January 2008. The diagnostic values were compared by calculating the area under the receiver operating characteristic curves (AUROCs). Using TE, the AUROC (95% CI) of liver stiffness was 0.80 (0.72–0.89) when discriminating between F ≤ 1 and F > 2, 0.93 (0.85–1.00) when discriminating between F ≤ 2 and F > 3 and 0.99 (0.97–1.00) when discriminating between F ≤ 3 and F4. For the diagnosis of F ≥ 3, the

AUROCs of TE were significantly higher than those obtained with the other four noninvasive indexes. Based on receiver operating characteristic curves, three cutoff values were chosen to identify F ≤ 1 (<7 kPa), F ≥ 3 (≥11 kPa) and F4 (≥14 kPa). Using these best cutoff scores, the negative predictive value and positive predictive value were 81.1% and 70.2% for the diagnosis of F ≤ 1, 96.3% and 60% for the diagnosis of F ≥ 3 and 100% and 57.1% for the diagnosis of F4. Thus, Transient elastography accurately predicted liver fibrosis and outperformed other simple noninvasive indexes in HIV/HCV-coinfected patients. Our data suggest that TE is a helpful tool for guiding therapeutic decisions in clinical practice.

Introduction

The HIV infection modifies the natural history of chronic hepatitis C, thus promoting more rapid progression to cirrhosis and end-stage liver disease.[1–3] Since the introduction of highly active antiretroviral therapy (HAART), chronic liver disease because of the hepatitis C virus (HCV) has become one of the most clinically relevant comorbid conditions in the HIV-infected population.[4,5] For this reason, all HIV-infected individuals with positive HCV-RNA should be considered as candidates for anti-HCV treatment, providing HIV infection is well controlled and there are no contraindications to therapy with interferon or ribavirin.[6]

Staging liver biopsy samples is considered an essential part of the management of patients with chronic hepatitis C because it provides prognostic information and, in many cases, assists in therapeutic decisions.[7] This is particularly true in HIV/HCV-coinfected patients because of the overall lower response to anti-HCV therapy and the potential interactions between antiretroviral and anti-HCV drugs.[8–10]

Because fibrosis implies morphological damage, liver biopsy has come to be considered the best standard for the assessment of liver fibrosis.[11] However, it has several limitations, including patient reluctance, adverse events, accessibility, cost, sampling error and interobserver variability.[12–14] In recent years, these limitations have led to an intensive search for alternative noninvasive procedures for staging liver fibrosis. These methods include assays based on serum biomarkers,[11] and transient elastography (TE), a technique that estimates the degree of fibrosis by measuring liver stiffness.[15,16]

Transient elastography is a rapid and user-friendly tool for early detection of significant fibrosis and cirrhosis and may have prognostic value in this setting. Although TE for HIV/HCV-coinfected patients has been evaluated in some trials showing values strongly correlated with METAVIR advanced fibrosis stages, an optimal TE cutoff for severe fibrosis and cirrhosis has yet to be established, and TE cutoff values must be optimized. The differences in the characteristics of each population, the prevalence of cirrhosis, or the presence of hepatic tissue inflammation or massive steatosis may have influenced the TE cutoffs assessed in the trials.[17,18] Thus, more studies are needed to address this issue.

In this prospective study, we aimed to determine the diagnostic accuracy of TE to predict fibrosis in HIV/HCV-coinfected patients, and to compare it with published noninvasive serum markers.

Methods

Patients

The study sample was composed of patients from the HIV outpatient clinic of two large teaching hospitals in Madrid, Spain. Patients with documented HIV/HCV coinfection who underwent liver biopsy and TE between January 2007 and January 2008 were included. Most liver biopsies were performed on patients who were potential candidates for HCV therapy. The inclusion criteria were as follows: no clinical evidence of hepatic decompensation, detectable HCV-RNA by polymerase chain reaction, negative hepatitis B surface antigen and absence of anti-HCV therapy between the date of liver biopsy and the date of TE. All patients gave their written informed consent for the liver biopsy and the Institutional Ethics Committee approved the study.

Liver Stiffness Measurements

Liver stiffness was measured using a FibroScan device (EchoSens, Paris, France), which is equipped with a probe consisting of an ultrasonic transducer mounted on the axis of a vibrator. The transducer transmits a mild-amplitude, low-frequency vibration, which sends an elastic shear wave through the liver parenchyma. At the same time, pulse-echo ultrasound acquisitions follow the propagation of the shear wave, enabling its velocity to be measured. This velocity is directly related to tissue stiffness. Results are expressed in kilopascals (kPa).

Transient elastography was performed no more than 6 months after the liver biopsy by the same trained personnel at each institution. Measurements were taken on the right lobe of the liver, through the intercostal spaces with the patient lying in dorsal decubitus and the right arm in maximal abduction following well-described instructions.[19] Ten validated measurements were taken for each patient. The success rate was calculated as the number of validated measurements divided by the total number of measurements. The median value was considered representative of liver stiffness. The validity of TE results was assessed using two parameters: (a) the interquartile range (IQR), which ensures that the variability of the validated measures did not exceed 30% of the median value and ( only procedures with 10 validated measurements and a success rate of at least 60% were

accepted.

Liver Biopsy

Ultrasound was routinely used to determine the percutaneous biopsy site. Liver biopsies were 25 mm in length in most cases. Formalin-fixed, paraffin-embedded liver tissue sections were stained by haematoxylin–eosin, Mason's trichrome and Perls' iron, and were evaluated by an experienced pathologist at each centre who had no knowledge of the patient's clinical and laboratory data. Liver fibrosis was estimated following the criteria established by the METAVIR ative Study Group.[20] Fibrosis was scored as follows: F0, no fibrosis; F1, portal fibrosis; F2 periportal fibrosis or rare portal-portal septa; F3, fibrous septa with architectural distortion, no obvious cirrhosis (bridging fibrosis) and F4, definite cirrhosis.

Noninvasive Markers of Liver Fibrosis

For purposes of comparison with TE, we evaluated four previously reported simple models that use routine parameters to predict liver fibrosis: the Forns index, which was developed to discriminate between HCV-monoinfected patients with and without significant liver fibrosis;[21] the AST-to-platelet ratio index (APRI), developed to predict both significant fibrosis and cirrhosis in HCV-monoinfected patients;[22] the FIB-4 index, developed to predict both significant fibrosis and advanced fibrosis in HIV/HCV-coinfected patients[23] and the HGM-2 index, developed to predict advanced fibrosis in HIV/HCV-coinfected patients.[24] Serum markers were measured from

an overnight fasting blood sample taken on the same day as the liver biopsy.

Statistical Analysis

The diagnostic performance of liver stiffness for different METAVIR fibrosis stages was assessed using receiver operating characteristic curves constructed to compare the absence and presence of significant fibrosis (F ≤ 1 vs F ≥ 2) and the absence and presence of advanced fibrosis (F ≤ 2 vs F ≥ 3). We evaluated the relationship between TE and liver fibrosis stage using Kendall's correlation coefficients. We also determined optimal cutoff values of TE for F ≤ 1 vs F ≥ 2, F ≤ 2 vs F ≥ 3 and F ≤ 3 vs F4 based on the highest negative predictive values (NPV) with an acceptable positive predictive value (PPV) higher than 50%. The diagnostic values of all five noninvasive methods were compared by calculating the area under the receiver operating characteristic curves (AUROCs). All data were analysed using SPSS, version 14.0 (SPSS Inc., Chicago, IL,

USA).

Results

Patients

During the study period, 105 patients with documented HIV/HCV coinfection underwent liver biopsy and TE. None of them had clinical or biological signs suggestive of cirrhosis. Five patients were excluded from the analysis because of unsuccessful interpretation of the liver biopsy results (n = 3) or unsuccessful liver stiffness measurement (n = 2). A total of 100 patients were analysed; their characteristics and the distribution by fibrosis stage and activity grade are shown in Table 1.

Correlation between Transient Elastography and Histology

Liver stiffness measurements ranged from 2.7 to 43.5 kPa. The median (IQR) of liver stiffness (in kPa) according to the different stages of fibrosis was as follows: F0, 4.9 (4.1–6.5); F1, 6.1 (5.3–8.6); F2, 8.4 (5.8–10.5); F3, 11.9 (8.8–16.6) and F4, 31.4 (22.5–40.3; Fig. 1). Liver stiffness was significantly correlated with the fibrosis stage (Kendall's tau-beta 0.5; P < 0.0001). The AUROC (95% CI) for liver stiffness was 0.80 (0.72–0.89) when discriminating between F ≤ 1 and F > 2, 0.93 (0.85–1.00) when discriminating between F ≤ 2 and F > 3 and 0.99 (0.97–1.00) when discriminating between F ≤ 3 and F4.

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Figure 1.

Distribution of liver stiffness according to the different stages of fibrosis.

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Figure 1.

Distribution of liver stiffness according to the different stages of fibrosis.

Diagnostic Accuracy of Transient Elastography for Fibrosis Staging

We assessed the diagnostic accuracy of TE for different categories of fibrosis. Based on the AUROC curves, three cutoff values were chosen to identify F ≤ 1 (<7 kPa), F ≥ 3 (≥11 kPa) and F4 (≥14 kPa). Using these best cutoff scores, the NPV to exclude F ≥ 2 was 81.1% and the PPV to confirm F ≥ 2 was 70.2%. Likewise, the NPV to exclude F ≥ 3 was 96.3%, and the PPV to confirm F ≥ 3 was 60.0%. Finally, the NPV to exclude F4 was 100%, and the PPV to confirm F4 was 57.1% (Table 2).

We also compared the accuracy of TE with HGM-2, the Forns fibrosis index, APRI and the FIB-4 index for the diagnosis of advanced fibrosis (F ≥ 3). The AUROCs of TE were significantly higher than the AUROCs obtained with the other four noninvasive indexes (Fig. 2, Table 3).

Discussion

Liver stiffness correlates well with liver fibrosis stage and is very useful for assessing chronic liver damage of different aetiologies, especially chronic viral hepatitis,[25,26] in which the identification of patients with advanced fibrosis or cirrhosis and those with mild or no liver fibrosis has important implications for clinical practice. Patients with a higher fibrosis stage have a poor prognosis, and antiviral therapy, particularly if a sustained virological response is achieved, is associated with improved survival.[27,28] Moreover, patients with established liver cirrhosis must be continuously screened for oesophageal varices and hepatocellular carcinoma. In patients with mild or no liver fibrosis, disease progression is likely to be

slow, and periodic monitoring is a reasonable alternative to antiviral therapy.[29,30]

Transient elastography is a recently developed technique for the assessment of liver stiffness. We studied the performance of TE in HIV/HCV-coinfected patients and found a significant correlation between liver stiffness and advanced fibrosis. Our study confirms TE as an efficient technique for the diagnosis of advanced liver fibrosis and cirrhosis. It may also prove useful when discriminating between patients with mild and no fibrosis. We also show that liver stiffness has greater diagnostic accuracy in advanced fibrosis and cirrhosis than simple noninvasive serum markers such as the Forns index, APRI, FIB-4 and HGM-2.

In order to select the best cutoff points for the diagnosis of advanced liver fibrosis and cirrhosis, we looked for those with the highest NPV and an acceptable PPV. Therefore, using a cutoff of 11 kPa, the NPV is as high as 96% for the exclusion of advanced fibrosis (≥F3). A cutoff of 14 kPa gives an NPV of 100% for cirrhosis.[31,32]

Both the cutoff values and the accuracy of TE for the diagnosis of advanced fibrosis and cirrhosis found in our study are within the ranges published for HCV-monoinfected patients and HIV/HCV-coinfected patients. In a single-centre study with 183 consecutive HCV-monoinfected patients, TE was the most accurate diagnostic technique for cirrhosis and advanced fibrosis. Cutoff values were 9.5 kPa for advanced fibrosis and 12.5 kPa for cirrhosis.[16] In another multicentre study with 327 HCV-monoinfected patients, TE performed best for the identification of cirrhosis and advanced fibrosis. Optimal stiffness cutoff values were 8.7 and 14.5 kPa for significant fibrosis and cirrhosis, respectively.[26] In a study that assessed 76 consecutive

HIV/HCV-coinfected patients who underwent liver biopsy and TE simultaneously, a liver stiffness cutoff of 14.6 kPa was found to be highly accurate for the diagnosis of cirrhosis.[31] Vergara et al., who studied 169 HIV/HCV-coinfected patients (123 with liver biopsy and 46 with liver cirrhosis based on clinical, biological and/or imaging criteria), observed that the same cutoff of 14.6 KPa was accurate for cirrhosis.[32]

Of note, we found that, for the diagnosis of advanced fibrosis and cirrhosis, TE outperformed the other noninvasive serum markers of fibrosis. This is consistent with the results of a recent study (72 consecutive HIV/HCV-coinfected patients who underwent a simultaneous liver biopsy and liver stiffness measurement), in which TE performed significantly better for the diagnosis of cirrhosis than the AST/ALT ratio, APRI and FIB-4.[31]

As for the ability of TE to discriminate between lower fibrosis stages (≤F1), other authors have suggested that, when liver stiffness values range from 2.5 to 7 kPa, mild or no fibrosis is likely.[17] In our experience, a cutoff value of 7 kPa gave a PPV of 70% (i.e. 70% certainty for the presence of F ≥ 2) and an NPV of 80% (i.e. 80% certainty for the presence of F < 2), suggesting that TE may also be useful when discriminating between patients with mild or no fibrosis and those with significant fibrosis. However, TE was not as accurate for this purpose as for the diagnosis of advanced fibrosis and cirrhosis, a result that was also observed by other authors[32] in a recent study that included 142 HIV/HCV-coinfected patients

who had undergone liver biopsy and TE to determine the ability of TE to discriminate between mild fibrosis (F ≤ 1) and moderate-to-severe fibrosis (F ≥ 2). The authors attempted to establish two different cutoffs to enhance the usefulness of TE in differentiating between mild and moderate fibrosis, with 6 kPa (PPV 54, NPV 90) as the cutoff value with highest ability to detect the absence of F ≤ 2 and 9 kPa (PPV 85, NPV 91) as the cutoff with the highest ability to detect F ≥ 2. The percentages of patients misclassified using these two cutoffs were 18% and 17% for ≤F0–F1 and ≥F2, respectively. In our study, using a cutoff of 7 kPa to discriminate between the presence and absence of ≥F2 led to a 19% misclassification rate.

We analysed four different noninvasive markers of liver fibrosis in more than 95% of our population and compared them with TE for the diagnosis of advanced liver fibrosis. TE was superior in all comparisons, and we think these noninvasive markers are mainly useful for patients in whom it is impossible to measure liver stiffness or in patients with heterogeneous liver stiffness values. Using noninvasive score markers for the diagnosis of significant fibrosis did not prove useful (data not shown); therefore, they do not complement TE results. Similarly, Cacoub et al. [33] published a study comparing seven noninvasive biological markers for the diagnosis of significant fibrosis, advanced fibrosis or cirrhosis in HIV/HCV-coinfected patients. They included APRI, FIB-4 and the Forns index, and the AUROCs reported are similar to ours. Only

biological markers, which include special parameters such as hyaluronic acid or alpha-2 maroglobulin proved accurate for differentiating between those with mild-to-moderate fibrosis and those with advanced disease. They did not compare biological markers with TE, but the results of the best noninvasive biological markers were inferior to those for TE in our study and in others.[31,33]

We found little information for HIV/HCV-coinfected patients about the comparative diagnostic accuracy of TE compared with other noninvasive indexes that incorporate direct markers of fibrosis (Fibrotest, Hepascore and Fibrometer), which have been shown to be better than indirect markers in this population group.[33]

Our study has some limitations. First, and in common with other authors, we observed discordant results for liver biopsy and TE. One possible explanation for these discrepancies is the underestimation of liver fibrosis by liver biopsy. It is well known that a needle liver biopsy removes approximately 1/50 000 of the total organ tissue, and therefore, the potential for sampling error is substantial.[11,13,34,35] TE, on the contrary, measures liver stiffness as a cylindrical volume 1 cm in diameter and 4 cm in length, that is, 500 times larger than the biopsy specimen.[25,26] Another possible explanation for the discrepancies is the overestimation of fibrosis by TE, because components of the liver parenchyma other than fibrous tissue, such as

inflammatory cells and fat, may increase liver stiffness.[36,37] Although two groups[17,26] have observed that the correlation between liver stiffness and fibrosis stage is not affected by steatosis, more evidence on the role of this condition in staging must be found.

Second, our study included only 15 patients with advanced fibrosis or cirrhosis, indicating that the prevalence of these conditions is low in this group. We think the population we studied is more representative of current HIV/HCV-coinfected patients than those included in previous studies, with a higher proportion (57%) of patients in stage F0–F1.[31,32] Moreover, TE performed well in the diagnosis of cirrhosis and advanced fibrosis. Therefore, although the low number of patients with cirrhosis or advanced fibrosis in our study population could be considered a limitation, we believe that it reflects the reality of current clinical practice in this setting.

In conclusion, TE accurately diagnosed advanced liver fibrosis and cirrhosis in HIV/HCV-coinfected patients, and may be useful to discriminate between mild and no fibrosis. We also found that FIB-4, APRI, the Forns index and the HGM-2 score did not perform as well in the diagnosis of advanced fibrosis as TE in this group.

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Figure 2.

AUROCs for noninvasive markers and transient elastography for the diagnosis of advanced fibrosis.