Special Considerations for the Use of the Transient Elastography Paediatric Probe, Compared to the Standard M Probe, Indirect Serological Markers and Histology

A retrospective cohort study, including all patients younger than 18 years of age with chronic liver disease who underwent a transient elastography, was performed. The study was carried out in the joint Unit of Paediatric Complex Hepatology and Liver Transplant, encompassing two third level paediatric hospitals, between 2015 and 2019. The study protocol was approved by local ethic committee (identifier code: PR(AMI)147/2019) and informed consent was signed by patient's legal guardians and patients over 16 years old.

Liver stiffness was assessed with FibroScan® (Echosens, France, model 502, class IIa, year 2010), which was performed by an experienced operator to avoid interobserver bias and in the same standardized conditions (fasting, decubitus position, right arm in maximal abduction, transducer placed over the right lobe). S probe (model 8; 5 MHz; diameter 5 mm), that measures depths ranging from 15-50 mm (S1: 15-40 mm; S2: 20-50 mm), was selected if chest circumference (CC) < 75 cm (S1: ≤ 45 cm; S2: 45-75 cm). M probe (3.5 MHz; diameter 7 mm), measuring depths range 35-75mm, was used if CC ≥ 75 cm. Both probes met the calibration terms. Elastographic parameters studied were: stiffness (KPa), interquartile range (IQR) and success rate (SR). Adult-validated liver stiffness measurement ranges to classify the fibrosis degree were taken as a reference: F0-F1 (≤7.6 KPa), F2 (7.7-9.4 KPa), F3 (9.5-14 KPa) and F4 (>14 KPa). The examination was successful when the median of at least 10 valid values, had a SR higher than 60% and with an IQR/LSM lower than 30%.

The following sociodemographic, clinical and analytical data were collected: age, sex, underlying liver disease and analytical parameters (alanine aminotransferase (ALT) U/L, aspartate aminotransferase (AST) U/L, gamma glutamyl transferase (GGT) U/L, total bilirubin (mg/dl), cholesterol (mg/dl), platelets (109/L), prothrombin time (%)). The following liver fibrosis test Scores were calculated using the obtained data:

• Fibrosis 4 Score (FIB-4) = Age (years) x AST (U/L) / platelets (109/L) x √ALT (U/L).
• AST to Platelet Radio Index (APRI) = AST (upper normal limit) (UI/l)/ platelets x 109 x 100.

Eighteen clinically indicated liver biopsies were performed and staged according METAVIR score (F0-F4). Blood test, fibrosis scores and biopsies were performed within 6 months of transient elastography. No clinical or analytical changes were observed during this period.