Simultaneous assessment of intestinal permeability and lactase activity in human-milk-fed preterm infants by sugar absorption test: Clinical implementation and analytical method

Background & aims: Experimental (nutritional) interventions in preterm infants frequently focus on intestinal maturation, as improving tolerance to enteral nutrition is a major goal. Intestinal permeability and lactase activity serve as markers for intestinal maturation. We aimed to develop a protocol for the simultaneous assessment of both markers in human-milk-fed preterm infants by a sugar absorption test. In addition, we developed a new gas chromatography-mass spectrometry (GC–MS) method for the analysis of lactulose, lactose, and mannitol in urine and milk collected during the sugar absorption test. Methods: The sugar absorption test was performed on days 4, 7, and 14 postpartum in 12 preterm infants (gestational age of 26–32 weeks). Human milk was collected, pooled, and divided into equal portions to provide a stable lactose intake for 24 h. Urine was collected in the last 6 h of this 24 h period, after administration of a bolus test sugar solution. Samples were analyzed by GC–MS after derivatization by oxime formation combined with acetylation. Results: The GC–MS method was validated and used for the accurate measurement of lactulose, lactose, and mannitol concentrations. The urinary lactulose/mannitol ratio declined with time, suggesting a decreased intestinal permeability. The urine-to-milk-lactulose/lactose ratio increased as a result of increased lactase activity with time. Conclusions: The developed protocol for simultaneous assessment of intestinal permeability and lactase activity can be used to monitor the effect of experimental (nutritional) interventions in human-milk-fed preterm infants. Urine and milk samples obtained during the sugar absorption test can be accurately analyzed by GC–MS.