False-Positive Liver Stiffness: Food, Transaminases, Cholestasis, Congestion, and M/XL Probe Selection in Obesity
Factors of False Elevation in Liver Stiffness
Liver stiffness assessed by VTQ (ARFI) is falsely elevated in the following situations (EFSUMB Course Book, 2018):
- postprandial state;
- elevated levels of aminotransferases;
- right ventricular failure (congestion);
- extrahepatic cholestasis.
Regarding elevated transaminases, VTQ (ARFI) appears less affected by moderately elevated values (within 2–5 × the upper limit of normal) compared to transient elastography (TE).
Steatosis as a Confounder in NAFLD
According to WFUMB/Ferraioli et al. (2018), in NAFLD, significant steatosis can be a confounder, leading to overestimation of LSM in patients with low fibrosis levels and overestimation of liver fibrosis. In patients with obesity and high degrees of steatosis, TE with the M-probe may be less accurate in diagnosing severe fibrosis in NAFLD; additional studies are needed on the impact of steatosis on LSM measured with the XL-probe, as the XL-probe provides lower stiffness values than the M-probe.
Selection of M- and XL-Probes in Obesity
In almost all studies, obesity was the main cause of unreliable LSM; however, the use of the M-probe was the primary limitation, leading to higher LSM values and a higher rate of false-positive results. This limitation is partially overcome by using the XL-probe (Ferraioli et al., 2018).
It has been reported that the XL-probe provides threshold values 1.5–2 kPa lower than those obtained with the M-probe, which must be considered when interpreting results.
Threshold Values for F3 Fibrosis in NAFLD (M-Probe)
| Threshold (M-Probe) | Purpose | Characteristic |
|---|---|---|
| 7.9 kPa | Rule out F3 | 90% sensitivity |
| 9.3 kPa | Rule in F3 | 90% specificity |
These thresholds are provided for NAFLD and the M-probe (EFSUMB Course Book, 2018). Lower threshold values apply to the XL-probe.
Frequently asked questions
In which conditions is liver stiffness by ARFI falsely elevated?
In postprandial states, elevated aminotransferase levels, right ventricular failure, and extrahepatic cholestasis (EFSUMB, 2018).
Do elevated transaminases affect VTQ and TE equally?
No. VTQ (ARFI) appears less affected by moderately elevated transaminases (2–5 × the upper limit of normal) compared to TE.
Why is the XL-probe preferred in obesity?
The M-probe in obese patients yields higher LSM and a higher rate of false-positive results; the XL-probe partially mitigates this limitation (Ferraioli et al., 2018).
How do the thresholds for M- and XL-probes differ?
The XL-probe provides threshold values approximately 1.5–2 kPa lower than the M-probe.
What TE (M-probe) thresholds are used for F3 in NAFLD?
7.9 kPa to rule out F3 (90% sensitivity) and 9.3 kPa to rule in F3 (90% specificity).