Optimal threshold of controlled attenuation parameter with MRI-PDFF as the gold standard for the detection of hepatic steatosis

Abstract

The optimal threshold of controlled attenuation parameter (CAP) for the detection of hepatic steatosis using both M and XL probe is unknown in nonalcoholic fatty liver disease (NAFLD). Magnetic resonance imaging proton density fat fraction (MRI-PDFF) is an accurate and precise method of detecting the presence of hepatic steatosis that is superior to CAP. Thus, the aim of this study was to evaluate the diagnostic accuracy and optimal threshold of CAP for the detection of hepatic steatosis as defined by MRI-PDFF ≥ 5%. This prospective cross-sectional study included 119 adults (59% women) with and without NAFLD who underwent MRI-PDFF and CAP using either M or XL probe when indicated within a 6-month period at the NAFLD Research Center, University of California, San Diego. The mean ( ± standard deviation) age and body mass index were 52.4 (±15.2) years and 29.9 (±5.5) kg/m² , respectively. The prevalence of NAFLD (MRI-PDFF ≥ 5%) and MRI-PDFF ≥ 10% was 70.6% and 47.1%, respectively. The area under the receiver operating characteristic (AUROC) of CAP for the detection of MRI-PDFF ≥ 5% was 0.80 (95% confidence interval [CI], 0.70-0.90) at the cut-point of 288 dB/m and of MRI-PDFF ≥ 10% was 0.87 (95% CI, 0.80-0.94) at the cut-point of 306 dB/m. When stratified by the interquartile range (IQR) of CAP, we observed that an IQR below the median (30 dB/m) had a robust AUROC compared with an IQR above the median (0.92 [95% CI, 0.85-1.00] versus 0.70 [95% CI, 0.56-0.85]; P = 0.0117), and these differences were statistically and clinically significant.

Conclusion: The cut-point of CAP for presence of hepatic steatosis (MRI-PDFF ≥ 5%) was 288 dB/m. The diagnostic accuracy of CAP for the detection of hepatic steatosis is more reliable when the IQR of CAP is <30 dB/m. These data have implications for the clinical use of CAP in the assessment of NAFLD. (Hepatology 2018;67:1348-1359).

Figure 1. Distribution of CAP measurements stratified by hepatic fat content (MRI-PDFF)

CAP measurements increase with increase of liver fat content assessed by MRI-PDFF (Kruskal–Wallis test P < 0.001): MRI-PDFF <5% n=35, MRI-PDFF 5-10% n=28, MRI-PDFF≥10% n=56.

Figure 2. Diagnostic accuracy of CAP for the detection of hepatic steatosis

Receiver operating curves (ROC) and area under the ROC A. for the detection of hepatic steatosis defined by MRI-PDFF ≥ 5% B. for the detection of hepatic fat content ≥ 10% defined as MRI-PDFF ≥ 10%

Figure 3. Higher CAP value using XL compared to M probe when MRI-PDFF < 10%

CAP measurements and standard deviation are presented using M probe (pink bar) and XL probe (blue bar) stratified by hepatic fat content assessed by MRI-PDFF. CAP measurements were significantly higher using XL probe compared to M probe in the lower grade of hepatic fat content. p-value were determined using independent two-tailed t- test.

Figure 4. The diagnostic accuracy of CAP increase when IQR of CAP is <30 dB/m

Area under the receiver operating curves (AUROC) of CAP and 95 % confidence of interval for the detection of hepatic steatosis defined by MRI-PDFF ≥ 5% was significantly higher when IQR of CAP was below median (30 dB/m) n= 60 compared to AUROC of CAP when IQR of CAP n=59 was above median, p value 0.017 determined using the method by Hanley and McNeil.

Figure 5. Optimal strategy for the screening of NAFLD using CAP measurements and its IQR as validity criteria

CAP measurements are considered valid when IQR of CAP is below 30 dB/m and 10 valid measurements are achieved. If the valid CAP measurement is below the optimal threshold the patient is considered as non-NAFLD.