Feasibility study and control values of transient elastography in healthy children

Transient elastography (TE) is a new technique for the non-invasive assessment of liver fibrosis. The degree of fibrosis is equivalent to the liver stiffness measured in kilopascal (kPa). It is frequently used in adult patients with a mean normal stiffness of 4.4-5.5 kPa. Since 2008, liver stiffness can be measured even in small children and infants following the availability of a new probe with a smaller diameter (S-probe 5 mm) than the regular probe (M-probe 7 mm). We report control values for healthy children between 0 and 18 years and investigated the feasibility of this technique in a pediatric population. For control values, TE was performed in infants and children after exclusion of liver disease by medical history, clinical examination, blood investigation, and abdominal ultrasound. For feasibility analyses the results of all TE performed in our clinic were analyzed irrespective of the underlying disease. Liver stiffness was measured with the S-probe (thorax diameter <45 cm (S1) or 45-75 cm (S2)) and the M-probe (thorax diameter >75 cm) according to the manufacturer's recommendations. A total of 240 healthy children were analyzed to establish control values. The median liver stiffness was 4.7 kPa resulting in an upper limit of normal of 6.47 kPa. Median values of stiffness were significantly age dependent with 4.40, 4.73, and 5.1 kPa in children 0-5, 6-11, and 12-18 years (p=0.001) while the interquartile range decreased with age (0.8, 0.7, and 0.6 kPa). The resulting upper limit of normal (median plus 1.64 times standard deviation) was 5.96, 6.65, and 6.82 kPa. Girls between 11 and 18 years showed a significantly lower median stiffness than boys of the same age (4.7 vs. 5.6 kPa; p<0.005). Feasibility was tested in 975 consecutive liver stiffness measurements (LSM) in children 0-18 years of age. Patients with invalid LSM were significantly younger than those with valid LSM (5.8 vs. 9.7 years, p<0.0001), showed a significantly higher stiffness (10.2 vs. 6.17, p<0.0001), and examinations took significantly longer (202 vs. 160 s, p<0.0001). TE is technically possible in children of all age groups. The upper limit of normal increases significantly with age. Due to movement artifacts the measurement is reliable from the age of 6 without sedation. In younger children the number of invalid measurements increases significantly. Further studies are needed to asses the value of TE in the diagnosis and follow-up of liver disease in pediatric hepatology.