Reassessment of the biological variation of the lactulose mannitol test in healthy volunteers and in patients one year after bariatric surgery

The intestinal permeability is interesting to investigate because the
intestinal barrier plays an essential role in major physiological processes. A
non-invasive test like the lactulose mannitol test can be used to determine
intestinal permeability. This test is based on orally administering two sugars
and quantifying these in urine samples. Lactulose and mannitol are excreted
unmetabolized in urine, so the amount measured in the urine provides
information about the intestine's absorption. Lactulose is a sugar that leaks
through pores in between the enterocytes and usually is not absorbed. Mannitol
is absorbed by enterocytes. Increased intestinal permeability is shown as a
higher lactulose/mannitol ratio in the collected urine. The lactulose/mannitol
test is the most popular intestinal permeability test which has been used for
decades. At this very moment the lactulose/mannitol test is used in various
hospitals in the Netherlands, as well as in clinical studies all over the
world. The biological variation of the lactulose/mannitol ratio has been
assessed once in 1993 using gas-liquid chromatography. Information on the
biological variation of the lactulose/mannitol ratio is helpful for the
interpretation of results of studies and if population-based reference
intervals will be used for the lactulose/mannitol test. Nowadays the lactulose
mannitol test is performed by collecting urine for five hours after ingestion
of the sugars. However, more studies are performing the lactulose/mannitol test
by collecting urine for two hours. Scientific research has shown that the
lactulose/mannitol ratio of the urine of the first two hours specifically
reflects small intestinal permeability, while the lactulose/mannitol ratio of
urine after two hours also partly reflects colonic permeability.

Because more studies are performing the lactulose/mannitol test by collecting
urine for a shorter period of time, and because the biological variation has
been established long ago and with a different quantification technique, we
want to reassess the biological variation with the use of liquid
chromatography-mass spectrometry. We want to assess the biological variation in
urine collected for two hours, the total five hours and the last three hours.

We expect that the lactulose/mannitol ratio of 0-5 hour collected urine will
show more variation than 0-2 hour collected urine and 2-5 hour collected urine
because 0-5 hour collected urine shows both small intestinal as colonic
permeability. The permeability of the small intestine and colon is different
because both have different epithelial cells present, and because of
differences in anatomy.

The study aims to determine the biological variation of the lactulose mannitol
ratio. The variation (Cv) in the lactulose mannitol ratio of 0-2 hours urine
will be compared to the Cv of the lactulose mannitol ratio of 2-5 hours urine
and 0-5 hours urine.

The inter-individual variation will be assessed by comparing the results of
different individuals. The intra-individual variation will be assessed by
comparing the results of a single individual on different days.

Written valid informed consent for fasting will be obtained from all
participants before starting the study. Participants will also fill in their
bank account information for the incentive. After a minimum of eight hours or
overnight fast participants are asked to collect a baseline urine sample when
waking up in a plastic urine container. Then, the participants will ingest the
sugar solution and drink 200 ml of water to prevent dehydration. After
ingestion, the participants will collect urine in the "0-2 hour" container. At
the end of the first two hours, participants will void all urine left in the
bladder in the 0-2 hours-container to collect all urine of the first two hours.
Participants will drink another 200 ml of water to prevent dehydration. After
the first two hours, urine will be collected in a different urine container
labeled as *2-5 hours*. Right before the end of the five hour collection,
participants will void all urine left in the bladder in the 2-5 hours container
to collect all urine. Participants will deliver the urine containers at the
UMCG. The deadline is two days after the measurement. After one week the second
measurement takes place, and one week after the second measurement the third
can take place.

Ingestion of the sugar solution has no risks. Fasting could be uncomfortable
for participants, but also here there are no risks involved. Fasting will not
damage the body. Urinating in containers could be a burden, but since urinating
is a natural occasion the burden is expected to be negligible.