The mean for APRI was 0.58 in the F0–F1 group (range 0.20–4.80; median 0.31; SD 0.92) and 1.00 in the ≥F2 group (range 0.29–2.65; median 0.68; SD 0.88). Using the Mann-Whitney U test for unpaired samples, there was no statistically significant difference in APRI values between the 2 groups (P = 0.065, Table 1). The AUC for diagnosis of significant fibrosis (≥F2) was 0.74 (Table 4, Fig. 2), although this was not statistically significant (P = 0.066). The most discriminant cutoff value for significant fibrosis in ROC analysis was 0.4, with a sensitivity of 83%, a specificity of 58%, a PPV of 31%, and a NPV of 94%.
AST/ALT Ratio Index
The mean AST/ALT ratio index value was 1.37 in the F0–F1 group (range 0.66–3.50; median 1.28; SD 0.65) and 0.94 in the ≥F2 group (range 0.80–1.10; median 0.93; SD 0.10). Regarding the AST/ALT ratio index, there was no significant difference between patients with no/mild fibrosis and those with significant fibrosis (Mann-Whitney U, P = 0.162, Table 1).
The AUC for the diagnosis of significant fibrosis (≥F2) with the AST/ALT ratio index was 0.69 (Table 4, Fig. 2). This value was, however, not significant (P = 0.162). The optimal cutoff AUC value for the diagnosis of significant fibrosis was 1.1, with a sensitivity of 100%, a specificity of 63%, a PPV of 40%, and a NPV of 100%.
Combinations of ARFI and Serum Markers
We evaluated paired combinations of ARFI with either APRI or the AST/ALT ratio index, as well as all 3 markers together for the diagnosis of significant fibrosis. ROC analyses of individual noninvasive tests and in combination are shown in Table 4 and Figure 2. The best diagnostic value was obtained with the combination of ARFI and the AST/ALT ratio index, with a significant AUC of 0.83 and a P value of 0.013.
To our knowledge, this is the second study to evaluate the diagnostic accuracy of noninvasive tests in assessing significant liver fibrosis in pediatric patients with liver transplant. The present study shows the diagnostic value of ARFI, a newly developed method to estimate liver stiffness compared to and in combination with common serum markers such as APRI and the AST/ALT ratio index, for the assessment of significant liver fibrosis (≥F2).
After liver transplantation, LB is still the reference tool for assessing hepatic fibrosis and disease progression. To reduce the number of liver biopsies, the development of noninvasive tests to assess hepatic fibrosis has been an active area of research in recent years. The diagnostic performance of ARFI has been shown to be efficient and superior to that of APRI and AST/ALT ratio index. When combining ARFI with the other serum markers, the most accurate diagnosis was achieved with ARFI+AST/ALT ratio index, which not only presented a higher AUC but also was clearly significant.
In our study, the AUC of ARFI test for significant fibrosis (0.76) was slightly lower than that in the study of Noruegas et al (6) that demonstrated an AUC of 0.82. This difference could be explained by a greater number of patients in stage F3 of fibrosis and patients with cirrhosis (F4), resulting in an increase in ARFI diagnostic performance for significant fibrosis. Nevertheless, ARFI was the only independent predictor of significant hepatic fibrosis through multivariate logistic stepwise regression analysis.
The optimal value for the diagnosis of significant fibrosis (1.57 m/s) was intermediate between that demonstrated in the studies by Noruegas et al (1.39 m/s) (6) and Hanquinet et al (2 m/s) (13). Up until now, the only study to evaluate ARFI diagnostic performance for revealing fibrosis in children with liver transplant was carried out by Hanquinet et al (13); however, this was not a clear indication of the effectiveness of the method because only approximately 60% of the patients had undergone liver transplants. Further studies using larger samples of pediatric patients with liver transplant are needed to refine SWV cutoff points for significant fibrosis.
The elevated sensitivity (83%) and NPV (94%) suggest that ARFI could be reliably used for first-line prebiopsy evaluation, thus avoiding LB in certain patients, despite its borderline significance value (P = 0.052), which can be explained by the limited number of subjects in this study. The different types of approach (subxiphoid vs intercostal) in ARFI data acquisition were not compared. The choice of approach was based on individuals to obtain the best acoustic window. There are no published studies in patients who have undergone liver transplant concerning this subject, but it could be an interesting area to investigate.
Furthermore, the influence of the graft type (left split, right split, or whole) on SWV values was also not evaluated. In the literature, the only established finding is that measurements in the right hepatic lobe are more accurate for diagnosing liver fibrosis because the left lobe is more susceptible to respiratory and cardiac movements. This was observed both in adult and pediatric patients without transplant (14). So, in general, liver graft measurements should be performed in the right lobe.
Two children presented discrepant results with high SWV values, but no fibrosis in the LB specimen. One patient presented moderate necroinflammatory activity upon pathologic liver analysis, and frank elevation of ALT values in relation to acute graft rejection. This is in line with the studies that reported elevated values of liver SWV, assessed by ARFI elastography, associated with high degrees of necroinflammatory activity (17,18). Authors of these studies concluded that ARFI specificity decreased in the presence of necroinflammatory activity. Extensive inflammatory infiltration, hepatocyte swelling, and tissue edema were evoked as the confounding factors. The other patient presented a history of cholestasis in relation to biliary reflux in the afferent loop, mild elevation of AST and ALT levels, and normal LB. In the literature, some studies have been carried out with Fibrotest (Biopredictive, Paris, France) that showed that extrahepatic cholestasis increased liver stiffness, irrespective of fibrosis (19,20). This was because of an augmentation of hydrostatic pressure in the liver with extrahepatic cholestasis. The same process could, therefore, be observed with ARFI elastography, but further studies are required to confirm this.
Necroinflammatory activity and cholestasis are definitive confounding factors for the accuracy of ARFI in the diagnosis of fibrosis. These results draw attention to the relatively weak specificity of ARFI, and the requirement for biopsy in cases of high SWV values. If these patients were excluded from the study, the diagnostic performance of significant fibrosis with ARFI elastography would be even greater, with an AUC of 0.82.
The usefulness of APRI as a noninvasive test of liver fibrosis in pediatric patients with chronic liver disease is controversial. Yang et al (21) concluded that in children with nonalcoholic fatty liver disease, APRI revealed a significant difference between patients with mild and significant fibrosis. Conversely, McGoogan et al (8) concluded that APRI was not a good marker of fibrosis in children with chronic viral hepatitis. Although we did not find a significant difference between the 2 groups (F0–F1 and ≥F2), the AUC (0.74) was acceptable and similar to that of previous studies on children with chronic hepatitis B (22). The lack of patients with cirrhosis in our study could explain the absence of a significant difference between groups. The pathobiology of hepatic chronic disease shows that there is an early increase in AST levels and a late decrease in platelet count in disease progression.
The AST/ALT ratio index used in isolation was a weak predictor of fibrosis. This is in line with previous studies in children with nonalcoholic fatty liver disease (17), in which an AUC of 0.53 was observed. In our study, the AST/ALT ratio index failed to distinguish significant hepatic fibrosis from no/mild fibrosis in pediatric patients with liver transplant with the lowest AUC of 0.69, nonsignificant. Among patients with altered liver function tests, the majority of false-positive cases (n = 9, 69%) presented signs of acute or chronic rejection or necroinflammatory activity upon LB. In addition, we observed that some patients with normal liver function tests had significant fibrosis (n = 2, 12%); however, the AST/ALT ratio index in combination with ARFI showed improved sensitivity and specificity. This could constitute a good diagnostic tool for avoiding LB in children with normal SWV values and liver function. Although steatosis was not evaluated in the present study, Motosugi et al (23) suggested that fat deposition did not affect liver stiffness measurements by ARFI.
There are, however, some limitations to be considered in the interpretation of our study. This was a study conducted at a single hospital, and as such, both identified and unidentified confounding factors may have influenced the results. The present study is also limited because of its small sample size; in particular, there was a small number of patients with significant fibrosis (n = 6) and none with cirrhosis. If there were a larger sample size, results may be more expressive. The fact that the time interval between biopsy and blood sampling was extended up to 4 months constitutes, in our opinion, a relative limitation, because the development of liver fibrosis is usually slow after liver transplantation. Furthermore, this was observed only in a minority of the patients (16.6%). Because only 10% of patients underwent LB for clinical reasons, we believe that the potential confounding effect from the presence of rejection is low. Nevertheless, future studies performed with protocol biopsies only are preferable to eliminate all of the possible confounding factors.
According to our study, ARFI is a promising screening test for detecting significant liver fibrosis (≥F2) in pediatric patients with liver transplant. In future years, further multicentric prospective studies with larger series of patients, preferably 5 or more years after transplantation, and with available protocol biopsies are needed to define clear cutoff ARFI values and confirm the effectiveness of this method in diagnosing liver fibrosis in these patients.
1. Zhang KJ, Tung BY, Kowdley KV. Liver transplantation for metabolic liver diseases. Clin Liver Dis
2. Kerkar N, Hadzic N, Davies ET, et al. De-novo autoimmune hepatitis after liver transplantation. Lancet
3. Neumann UP, Langrehr JM, Neuhaus P. Chronic rejection after human liver transplantation. Graft
4. Evans HM, Kelly DA, McKiernan PJ, et al. Progressive histological damage in liver allografts following pediatric liver transplantation. Hepatology
5. Martin SR, Russo P, Dubois J, et al. Centrilobular fibrosis in long-term follow-up of pediatric liver transplant recipients. Transplantation
6. Noruegas MJ, Matos H, Gonçalves I, et al. Acoustic radiation force impulse-imaging in the assessment of liver fibrosis in children. Pediatr Radiol
7. Shima H, Igarashi G, Wakisaka M, et al. Noninvasive acoustic radiation force impulse (ARFI) elastography for assessing the severity of fibrosis in the post-operative patients with biliary atresia. Pediatr Surg Int
8. McGoogan KE, Smith PB, Choi SS, et al. Performance of AST to platelet ratio index (APRI) as a noninvasive marker of fibrosis in pediatric patients with chronic viral hepatitis. J Pediatr Gastroenterol Nutr
9. Friedrich-Rust M, Wunder K, Kriener S, et al. Liver fibrosis in viral hepatitis: noninvasive assessment with acoustic radiation force impulse imaging versus transient elastography. Radiology
10. Takahashi H, Ono N, Eguchi Y, et al. Evaluation of acoustic radiation force impulse elastography for fibrosis staging of chronic liver disease: a pilot study. Liver Int
11. Goertz RS, Zopf Y, Jugl V, et al. Measurement of liver elasticity with acoustic radiation force impulse (ARFI) technology: an alternative noninvasive method for staging liver fibrosis in viral hepatitis. Ultraschall Med
12. Goldschmidt I, Stieghorst H, Munteanu M, et al. The use of transient elastography and non-invasive serum markers of fibrosis in pediatric liver transplant recipients. Pediatr Transplant
13. Hanquinet S, Rougemont AL, Courvoisier D, et al. Acoustic radiation force impulse (ARFI) elastography for the noninvasive diagnosis of liver fibrosis in children. Pediatr Radiol
14. Toshima T, Shirabe K, Takeishi K, et al. New method for assessing liver fibrosis based on acoustic radiation force impulse: a special reference to the difference between right and left liver. J Gastroenterol
15. Batts KP, Ludwig J. Chronic hepatitis. An update on terminology and reporting. Am J Surg Pathol
16. Lackner C, Struber G, Liegl B, et al. Comparison and validation of simple noninvasive tests for prediction of fibrosis in chronic hepatitis C. Hepatology
17. Chen SH, Li YF, Lai HC, et al. Effects of patient factors on noninvasive liver stiffness measurement using acoustic radiation force impulse elastography in patients with chronic hepatitis C. BMC Gastroenterol
18. Arena U, Vizzutti F, Corti G, et al. Acute viral hepatitis increases liver stiffness values measured by transient elastography. Hepatology
19. Harata M, Hashimoto S, Kawabe N, et al. Liver stiffness in extrahepatic cholestasis correlates positively with bilirubin and negatively with alanine aminotransferase. Hepatol Res
20. Millonig G, Reimann FM, Friedrich S, et al. Extrahepatic cholestasis increases liver stiffness (FibroScan) irrespective of fibrosis. Hepatology
21. Yang HR, Kim HR, Kim MJ, et al. Noninvasive parameters and hepatic fibrosis scores in children with nonalcoholic fatty liver disease. World J Gastroenterol
22. Lebensztejn DM, Skiba E, Sobaniec-Lotowska M, et al. A simple noninvasive index (APRI) predicts advanced liver fibrosis in children with chronic hepatitis B. Hepatology
23. Motosugi U, Ichikawa T, Niitsuma Y, et al. Acoustic radiation force impulse elastography of the liver: can fat deposition in the liver affect the measurement of liver stiffness? Jpn J Radiol
Keywords:© 2014 by European Society for Pediatric Gastroenterology, Hepatology, and Nutrition and North American Society for Pediatric Gastroenterology,
acoustic radiation force impulse; aspartate aminotransferase/alanine aminotransferase index; aspartate-to-platelet ratio index; noninvasive diagnosis of liver fibrosis; pediatric liver transplantation