Formula weight for lactulose: 342.29 grams
Formula weight for L-rhamnose: 182.17 grams
Protocol (Lutgens et al):
(1) The patient fasts overnight.
(2) The urinary bladder is voided.
(3) The patient drinks 5.0 grams lactulose and 1.0 grams of L-rhamnose (often mixed with other sugars such as D-xylose and 3-O-methyl-D-glucose, see next sections) in an isotonic solution.
(4) Urine is collected for the next 5 hours.
(5) A light breakfast is permitted 2 hours after drinking the solution.
(6) The volume of the urine at 5 hours is measured and an aliquot is sent for testing.
(7) Measure the amount of lactulose and L-rhamnose in the urine.
urine excretion of lactulose in mg =
= (urine lactulose in mg/dL) * (urine volume in mL) / 100
percent of oral dose of lactulose in the urine =
= (urine excretion of lactulose in mg) / 5000 * 100%
urine excretion of L-rhamnose in mg =
= (urine L-rhamnose in mg/dL) * (urine volume in mL) / 100
percent of oral dose of L-rhamnose in the urine =
= (urine excretion of L-rhamnose in mg) / 1000 * 100%
lactulose to rhamnose ratio = L/R ratio =
= (percent of oral dose lactulose in urine) / (percent of oral dose L-rhamnose in urine)
Interpretation:
• The normal L/R ratio is <= 0.02 (others use <= 0.04).
• Following cytotoxic therapy or with sepsis, the gut integrity becomes disturbed, with the L/R ratio > 0.09.
• A ratio > 0.13 is considered severely abnormal.
