Lot-to-lot reagent changes and commutability of quality testing materials for total bile acid measurements

To the Editor,

Bile acids (BA) are synthesised in the liver through a multi-step process, beginning with cholesterol. Prior to active excretion into bile, they are conjugated with glycine or taurine. Once BA have entered the enterohepatic circulation, through the actions of gut microbiota, they undergo chemical modifications, including the removal of amino acids (deconjugation) and 7-alpha hydroxyl groups. This results in many BA species being present in serum, with proportions differing between pathological and non-pathological states. The diagnosis of intrahepatic cholestasis of pregnancy (ICP) is a diagnosis of exclusion, which is supported by the presence of increased serum total bile acids (≥19 μmol/L non-fasting; ≥10 μmol/L fasting) in a pruritic woman without other active liver pathology. ICP is associated with increased risks of spontaneous preterm birth with BA ≥40 μmol/L and of in utero fetal death with BA ≥100 μmol/L, with risk dependent on peak BA concentration. Optimal management of women with ICP remains uncertain, but early delivery is considered at >37 weeks for BA ≥40 μmol/L or >36 weeks for BA ≥100 μmol/L. Results of BA measurements can influence obstetric decision-making, leading to earlier interventions, and influencing iatrogenic preterm birth rates...