Direct comparison of the FibroScan XL and M probes for assessment of liver fibrosis in obese and nonobese patients.
BACKGROUND
A novel Fibroscan XL probe has recently been introduced and validated for obese patients, and has a diagnostic accuracy comparable with that of the standard M probe. The aim of this study was to analyze and understand the differences between these two probes in nonobese patients, to identify underlying causes for these differences, and to develop a practical algorithm to translate results for the XL probe to those for the M probe.


RESULTS
Both probes were directly compared first in copolymer phantoms of varying stiffness (4.8, 11, and 40 kPa) and then in 371 obese and nonobese patients (body mass index, range 17.2-72.4) from German (n = 129) and Canadian (n = 242) centers. Liver stiffness values for both probes correlated better in phantoms than in patients (r = 0.98 versus 0.82, P < 0.001). Significantly more patients could be measured successfully using the XL probe than the M probe (98.4% versus 85.2%, respectively, P < 0.001) while the M probe produced a smaller interquartile range (21% versus 32%). Failure of the M probe to measure liver stiffness was not only observed in patients with a high body mass index and long skin-liver capsule distance but also in some nonobese patients (n = 10) due to quenching of the signal from subcutaneous fat tissue. In contrast with the phantoms, the XL probe consistently produced approximately 20% lower liver stiffness values in humans compared with the M probe. A long skin-liver capsule distance and a high degree of steatosis were responsible for this discordance. Adjustment of cutoff values for the XL probe (<5.5, 5.5-7, 7-10, and >10 kPa for F0, F1-2, F3, and F4 fibrosis, respectively) significantly improved agreement between the two probes from r = 0.655 to 0.679.


CONCLUSIONS
Liver stiffness can be measured in significantly more obese and nonobese patients using the XL probe than the M probe. However, the XL probe is less accurate and adjusted cutoff values are required.
Department of Medicine and Center for Alcohol Research, Liver Disease and Nutrition, Salem Medical Center, Germany.
Esteban
E
Durango
Department of Medicine and Center for Alcohol Research, Liver Disease and Nutrition, Salem Medical Center, Germany.
Christian
C
Dietrich
Department of Medicine and Center for Alcohol Research, Liver Disease and Nutrition, Salem Medical Center, Germany.
Helmut Karl
HK
Seitz
Institute of Medical Biometry and Informatics, University of Heidelberg, Heidelberg, Germany.
Cornelia Ursula
CU
Kunz
Liver Unit, Centre Hospitalier de l'Université de Montréal, Hôpital Saint-Luc, Montréal, Quebec, Canada.
Gilles T
GT
Pomier-Layrargues
Toronto Western Hospital Liver Centre, Toronto, Ontario, Canada.
Andres
A
Duarte-Rojo
Multi-Organ Transplant Unit, University of Western Ontario, London, Ontario, Canada.
Melanie
M
Beaton
The Toronto Liver Centre, Toronto, Ontario, Canada.
Magdy
M
Elkhashab
Liver Unit, Division of Gastroenterology and Hepatology, Department of Medicine, University of Calgary, Calgary, Alberta, Canada.
Robert P
RP
Myers
Department of Medicine and Center for Alcohol Research, Liver Disease and Nutrition, Salem Medical Center, Germany ; Liver Unit, Centre Hospitalier de l'Université de Montréal, Hôpital Saint-Luc, Montréal, Quebec, Canada.
Sebastian
S
Mueller
M probe; XL probe; cirrhosis; liver fibrosis; liver stiffness; obesity; steatosis; transient elastography