October 03, 2017
2 min read

Noninvasive tests reliably exclude advanced fibrosis in low-risk patients

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Among low-risk patients, noninvasive scoring systems reliably excluded advanced fibrosis compared with fasting blood tests and transient elastography results, according to recently published data.

“Fibrosis has traditionally been assessed using liver biopsy as the reference standard, but this is not feasible for a disease with high prevalence because of logistics, safety concerns and cost,” Suzanne E. Mahady, MBBS, MMed, from the Sydney School of Public Health, University of Sydney, and colleagues wrote. “We evaluated the test performance of noninvasive scores in a general ambulatory population and provide data on diagnostic accuracy that can be used to inform the applicability of noninvasive scores in low-risk settings.”

The researchers used transient elastography as the reference standard to test the performance accuracy of the Nonalcoholic Fatty Liver Disease Fibrosis Score (NFS), Fibrosis-4 (FIB-4), and Aspartate Transaminase to Platelet Ratio Index (APRI) tests. The study cohort included 749 patients whom the researchers deemed typical of the population at large. Approximately 15 patients had advanced fibrosis, according to transient elastography.

The area under the receiver operating curve was 0.63 for NFS (95% CI, 0.46-0.81), 0.64 for FIB-4 (95% CI, 0.4-0.84), and 0.71 for APRI (95% CI, 0.56-0.88). One patient had a positive NFS and two patients had positive FIB-4 and APRI score.

Results of NFS testing showed a sensitivity for advanced fibrosis of 7% (95% CI, 0-32), a specificity of approximately 100% (95% CI, 99.2-100), a positive predictive value of 50% (95% CI, 1-99) and a negative predictive value of 98% (95% CI, 97-99). Regarding the positive predictive value, the researchers stated that “for every positive result, another would be a false-positive result; however, the true value is uncertain because of the wide CI.”

The FIB-4 and APRI tests both had a sensitivity of 13% (95% CI, 2-40), specificity of 100% (95% CI, 99-100), and a negative predictive value of 98% (95% CI, 97-99) for advanced fibrosis. After the researchers applied the lower thresholds for NFS and FIB-4, the sensitivity increased to 33% (95% CI, 9-57) for both tests, while the specificity was reduced to 91% (95% CI, 88-92) for NFS and to 87% (95% CI, 85-90) for FIB-4.

“Tests with a high specificity and negative predictive value are useful in clinical settings, because diagnostic uncertainty is minimized and follow-up testing can be avoided,” the researchers wrote. “This is particularly helpful in NAFLD, where the confirmatory tests are either risky, such as liver biopsy, or expensive with limited availability, such as transient elastography.”

The negative likelihood ratios for test accuracy at the upper threshold ranged from 0.87 (95% CI, 0.71-1.06) for both FIB-4 and APRI, to 0.93 (95% CI, 0.82-1.07) for NFS. According to the researchers, these results suggest the posttest probability of disease is not substantially altered in patients with negative results from noninvasive fibrosis tests.

“Noninvasive fibrosis scoring systems can reliably exclude the presence of advanced fibrosis in low-risk populations without the need for further testing, and with minimal risk of a missed diagnosis,” the researchers concluded. “However, scoring systems are insufficiently sensitive for case detection. Positive test results are associated with a high rate of false positives and should prompt further testing.” – by Talitha Bennett

Disclosure: The researchers report no relevant financial disclosures.