The ratio of urine lactulose to urine L-rhamnose (L/R ratio) is a measure of intestinal permeability. Lactulose is a large molecule and normally very little is absorbed from the gut. Following a variety of insults the gut becomes more permeable, and lactulose may be absorbed into the blood from which it passes into the urine.


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)



• 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.


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