Accurate assessment of fibrosis stage in persons infected with chronic hepatitis C virus (HCV) is important for management, understanding progression risk and determination of treatment urgency. Fibrosis assessment is particularly important in HIV/HCV co-infected patients because of the more rapid disease progression that has consistently been observed [1–4], diminished responses to therapy [5,6] and the need to consider antiretroviral therapy in conjunction with hepatitis C treatment decisions.
Liver biopsy is the standard of care for ascertainment of fibrosis. However, biopsy is invasive, expensive, associated with severe complications and highly subject to measurement error [7,8]. These limitations have driven a proliferation of noninvasive strategies or ‘surrogates’ for liver fibrosis. Noninvasive strategies have numerous advantages including lower cost and higher patient acceptability thus making them more amenable to repeat measurement across more frequent intervals then biopsy. Broadly, noninvasive strategies can be grouped into two categories: serum marker panels and imaging techniques. However, the degree to which these noninvasive strategies are currently used in clinical practice for HIV/HCV co-infected patients varies considerably by country and continent, with widespread use in some European countries and limited use in the USA.
The purpose of this review is to highlight new findings published in 2010–2011 related to noninvasive fibrosis assessment in HIV/HCV co-infected patients. Overall, we found 32 studies related to noninvasive strategies in HIV/HCV co-infected patients of which 15 were published in 2010–2011. We excluded two studies published in languages other than English.
Studies on serum marker panels focused on either validating established panels through comparison of multiple serum marker panels in the same population; establishing new panels using combinations of markers used in previously validated panels; or applying new methodology. A key challenge of marker panels applied to HIV/HCV co-infection is that the majority was developed specifically for HCV mono-infected patients and then subsequently applied to co-infected patients sometimes making performance sub-optimal. Table 1[9•–15•,16,17•,18•] illustrates the performance of all marker panels across the various studies conducted in 2010–2011. Serum marker panels included a combination of direct, indirect and both direct and indirect markers. Whereas direct markers of fibrosis actually reflect serum extracellular matrix (ECM) turnover, indirect markers reflect functional alterations in hepatic function and do not directly measure hepatic ECM metabolism. Accuracy of marker panels was generally measured by the area under the receiver operating characteristic curve (AUROC), which reflects the overall performance of the serum marker panel relative to the gold standard (biopsy), accounting for sensitivity and specificity across the full range of cut-points. The minimum possible value of the AUROC is 0.5; a perfect test would have a score of 1.0 but scores greater than 0.8 are generally considered very good.
Individual serum markers
Hyaluronic acid, a direct fibrosis marker, has been found to predict fibrosis and cirrhosis in HCV mono-infected patients alone and in combination with other markers but has not been widely evaluated alone in co-infection [15•,19]. In 2010–2011, hyaluronic acid was the only marker evaluated alone in terms of performance relative to the biopsy and marker panels. Resino et al.[9•] evaluated the performance of hyaluronic acid compared to HGM-1, HGM-2, Forns, aspartate aminotransferase (AST) to platelet ratio index (APRI) and FIB-4 among 201 HIV/HCV co-infected patients. The AUROC values for significant fibrosis (≥F2), advanced fibrosis (≥F3) and cirrhosis were 0.68, 0.77 and 0.86, respectively; these were comparable with performance of other indices. The only improvement over other panels was with respect to cirrhosis; using a low and a high cut-off, biopsy could be avoided in 52% of patients for diagnosis of cirrhosis. The advantage of using hyaluronic acid is that it only requires one test and is not likely to be affected by other factors associated with HIV, which can impact some of the markers included in the more simple noninvasive indexes. However, hyaluronic acid is not commonly measured in hospitals vs. the other indexes, which include markers that are routinely available in clinical practice. Overall, this study failed to demonstrate superiority of hyaluronic acid compared with these other markers.
Previously validated serum marker panels
Several studies applied previously validated marker panels to co-infected patients and drew comparisons across marker panels. All included APRI as one of the comparators. APRI has the advantage of using readily available laboratory tests and a simple calculation. However, a recent meta-analysis concluded that the primary utility of APRI is in excluding significant fibrosis . Two studies evaluated the performance of APRI in subgroups defined by CD4 and alanine aminotransferase (ALT). Most previous studies have included persons with high CD4 and elevated ALT. The first study by Singal et al.[11•] compared the performance of APRI among 106 co-infected patients to 105 HCV mono-infected patients. The median CD4 cell count among HIV/HCV co-infected patients was 430 cells/μl. Overall, the AUROC for predicting significant fibrosis was slightly lower in co-infected compared to mono-infected patients (0.77 vs. 0.86, P = 0.18) Notably, performance was substantially lower in those with CD4 cell counts below 250 cells/μl. (0.64 vs. 0.86, P = 0.05). Given this poor performance in the low CD4 strata, the authors compared the results with that of FIB-4, which did not have differential performance by CD4 strata. The conclusions of the prior meta-analysis that APRI has utility for excluding significant fibrosis were not supported by this study for patients with low CD4 cell counts .
The second study by Shah et al.[12•] compared APRI and FIB-4 among 295 biopsies from 237 HIV/HCV co-infected patients. The median CD4 among these patients was 525 cells/μl. Results were stratified by ALT (elevated vs. normal). Among those with elevated ALT, the AUROC for APRI was 0.76 for FIB-4 was 0.80. For those with normal ALT, performance was better (0.90 for FIB-4 and 0.85–0.95 for APRI). Whereas negative predictive value (for excluding fibrosis among those with a negative result) for both was high, positive predictive value (identifying significant fibrosis in those with a positive result) was low (0.50 for FIB-4 and 0.67 for APRI) even in those with normal ALT. Both appear to be able to accurately rule out fibrosis in patients with normal ALT; however, these findings support others in that positive predictive value is suboptimal .
Macias et al. compared APRI and Forns among 519 HIV/HCV co-infected patients from a multicenter study in Spain. The AUROC for detection of significant fibrosis for both was 0.67. Overall positive predictive value at established cut-offs was higher for APRI than Forns. Each panel on its own would have resulted in 22% of biopsies being avoided but a sequential application of APRI and then Forms could have avoided 30% of biopsies . Diagnostic yield improved slightly with biopsies greater than 15 mm in length, but overall the percentage of correctly classified was 10% lower than what has been previously observed [21–27].
New serum marker panels
Others sought to develop new marker panels using existing candidate markers to optimize performance in co-infected patients. For example, Cales et al.[17•] used components of the five marker panels that had previously been applied to HIV/HCV co-infected patients (e.g. APRI, FIB-4, FibroTest, FibroMeter and HepaScore) to determine whether a new marker panel developed from these components would have superior performance in co-infected patients. The study included 467 patients (183 derivation set, 284 validation set) from four centers in France. Two strategies were used: the components of FibroMeter, the highest performing panel, were considered and the components of all five marker panels were considered. The new FibroMeter panel determined from the components of FibroMeter to be specific to HIV/HCV co-infection was called FibroMeter HICV and the new panel developed from the five tests was called HICV and included variables (AST, α-2-macroglobulin and prothrombin index). Overall, for diagnosis of significant fibrosis, FibroMeter HICV and the HICV had the best performance in the derivation set (AUROC 0.83 and 0.82, respectively). Among existing panels, FibroMeter had the best performance (0.78) and APRI the worst (0.72). Performance in the validation sample diminished (0.74 and 0.74, respectively) but after the AUROC was weighted as a function of fibrosis stage and the reference population (Obuchowski index), performance improved. The authors also assessed other performance characteristics that account for biases related to disease prevalence (e.g. test performance profile, reliable diagnosis and diagnostic reproducibility). All three criteria supported HICV, FibroMeter HICV and FibroMeter as having highest performance.
Another new marker panel was developed by Resino et al.[15•] among 195 HIV/HCV co-infected patients (127 in derivation group and 68 in validation group). Using 14 candidate direct and indirect markers, they identified a panel of five markers (HGM-3) that included platelet count, alkaline phosphatase (ALP), hepatocyte growth factor (HGF), tissue inhibitor of metalloproteinase-1 (TIMP-1). The formula is as follows: x = −5.0596 − (1.210 × 10−2 × platelet) + (1.203 × 10−2 × ALP) + (1.220 × 10−3 × HA) + (4.526 × 10−4 × HGF) + (6.312 × 10−3 × TIMP − 1). Compared with HGM-2, FIB-4, APRI and Forns, the performance of HGM-3 was superior in terms of detecting advanced fibrosis (≥F3) and cirrhosis (≥F4) but comparable for significant fibrosis (≥F2). Two cut-offs were established; using the low cut-off in the validation set; only one false-negative was detected and with the high cut-off only three false-positives were detected.
Macias et al.[10•] examined direct markers MMP-2 and TIMP-1 in combination with routinely available data [including APRI, ALT, AST, gamma-glutamyl transferase (GGT), bilirubin, cholesterol levels and platelet counts] among 90 co-infected patients. AST, platelet count and MMP-2 were predictors of significant fibrosis (≥F2) and cirrhosis (≥F4). A score that included these variables had an AUROC of 0.76 for significant fibrosis and 0.88 for cirrhosis. Two cut-offs were identified for both significant fibrosis and cirrhosis; applying these cut-offs for significant fibrosis reduced the proportion of biopsies needed by 34%. The authors also explored using a sequential approach of APRI and MMP-2. Using this approach, all those with APRI below 1.5 would be tested with MMP-2 resulting in a reduction of 46% of biopsies.
Serum marker panels developed using novel methodology
The standard approach to development of serum fibrosis marker panels has been to identify a series of candidate markers, dichotomize individuals into two groups (e.g. fibrosis vs. no fibrosis) and use logistic regression and AUROC to assess performance of different combinations of markers. Whereas this approach has yielded a number of panels, there are inherent limitations. Two studies in the past year used novel approaches to overcome some of these limitations.
Resino et al.[14•] considered a artificial neural network approach (ANN) among 362 HIV/HCV co-infected patients. Compared with a simple regression model approach, these are computational models that incorporate a set of artificial neurons linked together through weighted connections. The weights for each connection can be established through examples and then the neural network can assign outputs (e.g. different outcomes) to new data that was not used in the learning process. In this analysis, they considered 10 markers (fibrinogen, glucose, AST, ALT, GGT, ALP, cholesterol, platelet, INR and age) that make up four validated marker panels (HGM-1, FIB-4, APRI and Forns) and compared predictive accuracy of the ANN with each panel alone. The ANN for significant fibrosis had an AUROC of 0.87 in the estimation set and 0.85 in the validation set; this was significantly higher than in the established panels. In general, predictive accuracy was higher for predicting presence of significant fibrosis (93% certainty) vs. absence (85% certainty).
A second study by Cales et al.[18•] focused on ‘optimizing’ serum marker panels through classification into multiple fibrosis stages vs. a dichotomous classification; an adapted vs. fixed diagnostic target; and developing a hyaluronic acid-free blood test (given expense and availability) with comparable accuracy and reliability with FibroMeter. The derivation population included 1056 patients from five centers in Europe and there were six validation subsets. Through bootstrap resampling, the robustness of each variable in the FibroMeter was assessed; hyaluronic acid appeared the least robust. Using stepwise logistic regression, a score that replaced hyaluronic acid with GGT was developed with no significant change in test performance (FibroMeter3G). Robustness was confirmed through bootstrap resampling in which each variable was selected in 63% of samples. FibroMeter2Gand FibroMeter3G demonstrated no significant differences in terms of diagnostic performance or ability to distinguish between fibrosis stages. The reduction in cost was 26 Euros. One of the validation populations included HIV/HCV co-infected patients and in this population of 176 individuals, the agreement between the FibroMeters was excellent with AUCs of 0.82 for FibroMeter2G and 0.83 for FibroMeter3G.
Transient elastography (FibroScan)
Imaging studies in 2010–2011 focused on transient elastography. Two studies focused on performance of transient elastography vs. the biopsy drawing comparisons with other noninvasive strategies (Table 2).
The first study by Sanchez-Conde et al.[13•] focused exclusively on HIV/HCV co-infected patients and compared transient elastography to APRI, Forns, FIB-4 and HGM-2. The AUROC for transient elastography for ruling out any fibrosis, identifying advanced fibrosis and cirrhosis were 0.80, 0.93 and 0.99, respectively. The following cut-offs were identified as most suitable to the data (<F1: <7 kPa; ≥F3: ≥11 kPa; and F4: ≥14 kPa). The AUROCs for transient elastography were significantly higher than Forns, APRI, FIB-4 and HGM-2.
A second study by Degos et al.[28•] focused on predictive accuracy of transient elastography vs. biopsy among HIV/hepatitis co-infected patients (n = 110) and compared to mono-infected patients (n = 913). Among HIV/HCV co-infected patients, the AUROC for cirrhosis and significant fibrosis was 0.95 and 0.84, respectively. Interestingly predictive accuracy was greater in co-infected vs. mono-infected patients. Compared with previously validated marker panels (e.g. FibroTest, FibroMeter, APRI, HepaScore), predictive accuracy was higher for transient elastography. Of note, data from the serum markers were not presented separately for co-infected vs. mono-infected patients. Cut-offs for transient elastography used in this study were 12.9 kPA for cirrhosis and 5.2 for fibrosis .
Other studies examined factors that might impact accurate classification of fibrosis/cirrhosis by transient elastography among HIV/HCV co-infected patients. A study by Neukam et al.[30•] assessed interobserver concordance of transient elastography among 188 patients and found that values of two independent observers were highly correlated (intraclass correlation index = 0.98) and yielded high kappa statistics for identification of cirrhosis (kappa = 0.89) [30•]. The kappa statistic was lower for significant fibrosis (0.60) but increased with use of two cut-offs (<6 and ≥9 kPa); however, with the two cut-offs, 46% in the middle range remained unclassified. Factors associated with lower agreement were high interquartile ranges and elevated triglycerides.
A second study by Sanchez-Conde et al.[31•] focused on factors associated with misclassification by transient elastography compared to biopsy in 110 patients. On the basis of a cut-off of 9.5 kPa to distinguish patients with advanced fibrosis (≥F3) from those without advanced fibrosis, misclassification rates were higher among patients with steatosis compared to those without (25 vs. 5%, P = 0.01). The majority of misclassifications in the steatosis group were false positive for ≥F3. A limitation of this study was that there was no information on body mass index, which is known to impact transient elastography results.
Overall, performance of transient elastography for the detection of fibrosis and cirrhosis among HIV/HCV co-infected patients appears superior to other previously validated and newly developed serum marker panels. However, there are still some concerns related to the accuracy, performance and widespread applicability of transient elastography. First, as has been previously demonstrated, steatosis appears to be associated with a high rate of misclassification. Second, studies continue to observe different optimal cut-offs for the designation of significant fibrosis and cirrhosis; the lack of standardized cut-points limits widespread applicability. Third, to date there are limited longitudinal data in either untreated or treated patients. Finally, transient elastography is still not widely available in many countries because of high cost and regulatory issues.
In terms of serum marker panels, when panels are developed specifically for use in HIV/HCV co-infection they appear to have superior performance compared to those developed for mono-infected patients. The recent studies confirm the limitations of APRI and support that its use should be primarily in excluding significant fibrosis; this appears to apply to all subgroups except those with low CD4 cell count. Panels like APRI, FIB-4 and Forns remain attractive because they are cheap and include widely available markers. Whereas performance of panels like HGM-3 and FibroMeter are superior, these panels include some nonroutine tests that may be expensive and not widely available. The panels that were newly developed (e.g. HGM-3, FibroMeter HICV) will require additional external validation before conclusions about their predictive accuracy can be made.
The work was supported by grants from the National Institute on Drug Abuse (DA04334, DA12568, DA16078 DA13806, and DA13868).
Conflicts of interest
There are no conflicts of interest.
References and recommended reading
Papers of particular interest, published within the annual period of review, have been highlighted as:
* • of special interest
* •• of outstanding interest
Additional references related to this topic can also be found in the Current World Literature section in this issue (p. 567).
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This study demonstrated that performance of APRI was suboptimal in persons with low CD4 cell counts (<250 cells/μl).
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This study demonstrated that APRI and FIB-4 are useful for exclusion of significant fibrosis even in those with normal ALT. Neither marker had high positive predictive value.
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This study demonstrated that transient elastography was superior to other serum marker panels in diagnosis of fibrosis and cirrhosis.
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The authors used artificial neural network methodology to improve the diagnostic accuracy of current marker panels.
15•. Resino S, Micheloud D, Miralles P, et al. Diagnosis of advanced fibrosis in HIV and hepatitis C virus-coinfected patients via a new noninvasive index: the HGM-3 index. HIV Med 2010; 11:64–73.
This study established a new mark panel specifically for HIV/HCV co-infection (HGM-3) that has high diagnostic accuracy for the diagnosis of bridging fibrosis and cirrhosis.
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17•. Cales P, Halfon P, Batisse D, et al. Comparison of liver fibrosis blood tests developed for HCV with new specific tests in HIV/HCV co-infection. J Hepatol 2010; 53:238–244.
In this study, the authors developed two new marker panels exclusively for the diagnosis of fibrosis/cirrhosis in HIV/HCV co-infected patients. The panels were called FibroMeter HICV and HICV.
18•. Cales P, Boursier J, Bertrais S, et al. Optimization and robustness of blood tests for liver fibrosis and cirrhosis. Clin Biochem 2010; 43:1315–1322.
The authors used bootstrapping methodology to validate and adapt the FibroMeter panel to be free of hyaluronic acid.
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28•. Degos F, Perez P, Roche B, et al. Diagnostic accuracy of FibroScan and comparison to liver fibrosis biomarkers in chronic viral hepatitis: a multicenter prospective study (the FIBROSTIC study). J Hepatol 2010; 53:1013–1021.
This study demonstrated that transient elastography performed equally well in HIV/HCV co-infected patients compared with mono-infected patients and was superior to other marker panels.
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30•. Neukam K, Recio E, Camacho A, et al. Interobserver concordance in the assessment of liver fibrosis in HIV/HCV-coinfected patients using transient elastometry. Eur J Gastroenterol Hepatol 2010; 22:801–807.
This study demonstrated high interobserver agreement for transient elastography. Transient elastography concordance was affected by high interquartile ranges and high triglycerides.
31•. Sanchez-Conde M, Montes Ramirez ML, Bellon Cano JM, et al.
Impact of liver steatosis on the correlation between liver stiffness and fibrosis measured by transient elastography in patients coinfected with human immunodeficiency virus and hepatitis C virus. J Viral Hepat 2011; 18:e278–e283.
Concordance between transient elastography and biopsy was affected negatively by liver steatosis.