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11-10-2011 | Gastroenterology | Article

Biochemical method equals transient elastography in fibrosis detection


Free abstract

MedWire News: The aspartate transaminase (AST) to platelet ratio index (APRI) is as good as transient elastography for the detection of significant liver fibrosis in patients with chronic hepatitis B (CHB), Indonesian researchers report.

"The presence of significant liver fibrosis is important to initiate antiviral therapy in CHB patients," explain Rinaldi Lesmana (University of Indonesia, Jakarta) and colleagues.

Liver biopsy has been the gold standard for the assessment liver histopathology, but it is invasive and inconvenient for the patient, and is also associated with substantial variability, even when performed by an experienced physician.

Transient elastography (TE) is a new, noninvasive, reproducible method for assessing liver fibrosis. It measures liver stiffness values expressed in kilopascals (kPa), but is not available for use in a primary care setting.

The APRI is another noninvasive method, which combines biochemical markers to predict liver inflammatory activity and fibrosis in CHB patients. It is calculated as serum AST (in U/l) divided by the upper limit of normal of AST then multiplied by 100 and divided by the platelet count (in 109/l).

The researchers say that APRI is more cost-effective than TE because it can be performed at no additional cost other than routine blood and liver functions tests.

To compare the diagnostic accuracy of the two tests in detecting significant liver fibrosis, Lesmana and team studied 117 (mean age 4 years, 54% men) patients with CHB.

Liver biopsy identified 73 (62.4%) patients with significant liver fibrosis, defined as stage F2 or greater according to the METAVIR scoring system. These patients had perivenular or pericellular fibrosis affecting zones 3 and 2 (stage F2), septal or bridging fibrosis (F3), or cirrhosis (F4).

The median liver stiffness assessed by TE was 5.9 kPa, while the median APRI was 0.24.

The researchers report that liver stiffness and APRI increased with the increasing fibrosis stage. Mean liver stiffness was significantly higher in patients with significant liver fibrosis compared with those with F0-F1 fibrosis (9.3 vs 6.0 kPa). APRI was also significantly higher in F2 and greater liver fibrosis patients than in those with F0-F1 fibrosis (0.41 vs 0.24).

Receiver operating characteristic (ROC) curve analysis showed comparable diagnostic accuracy between APRI and TE in detecting significant fibrosis

The optimal cut-off value for TE liver stiffness was 5.85 kPa. At this level, the area under the ROC curve (AUC) was 0.61, sensitivity and specificity were 60.3% and 63.6%, respectively, and the positive and negative predictive values were 73.3% and 49.1%, respectively.

The researchers note that diagnostic accuracy improved significantly when applied to fibrosis of F3 and greater (adjusted AUC 0.867 with 7.0 kPa as a cut-off value).

The AUC at the optimal APRI cut-off of 0.235 was slightly higher than that for TE, at 0.693, indicating a greater ability to discriminate between patients with and without significant liver fibrosis. At this cut-off the sensitivity and specificity of APRI were 64.5% and 70.5%, respectively, while the positive and negative predictive values were 78.3% and 54.4%, respectively.

"We endorse the use of APRI as a screening tool in primary care to detect significant liver fibrosis," conclude Lesmana and co-authors in the Journal of Clinical Pathology.

They caution, however that "liver biopsy is still needed when APRI or TE results are inconclusive, especially in patients with mild fibrosis."

By Laura Dean

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