Chemistry Reference
In-Depth Information
which express lactase (Villako and Maaroos, 1994) and hence a genetically
persistent individual may be classified as a maldigester in this instance. Also,
the use of antibiotics may disrupt the gut flora and result in erroneous results.
Colonic adaptation to dairy products may affect breath hydrogen production by
increasing bacterial populations that have increased metabolic activity for lactose
(Hertzler and Savaiano, 1996). Also, some individuals will be 'hydrogen non-
producers' (as a result of having a sterile gut or a hostile gut pH with acidity too
severe for the existence of hydrogen-producing bacteria), and in this situation the
breath hydrogen test would be uninformative.
In the clinical setting, there are ways of improving the quality of the test.
These include retesting, and giving a dose of lactulose to test for hydrogen
production, and investigation of other causes of the lactose intolerance.
A recent study by members of our group (Mulcare et al., 2004)
attempted to estimate the error in both the blood glucose and the breath
hydrogen test from published data. Results were pooled from papers that
compared either indirect method with each other or with a verified phenotype
based on direct enzyme assays from jejunal biopsy. Exact protocols varied
between the pooled data set, but all included a minimum 50 g lactose load and
measured a change in the parameter one or more times between 30 min and
4 h after ingestion. The error of the blood glucose method was 7% false
positive (i.e. non-persistent individuals classified as lactose digesters) and
9% false negative (i.e. persistent individuals classified as lactose malabsor-
bers). The breath hydrogen method was found to give a slightly more accurate
assessment of lactase persistence status, with approximately 5% false positive
and 7% false negative error. Thus, the evidence suggests that to obtain the
most accurate indirect assessment of lactose tolerance status, a breath hydro-
gen test should be undertaken. The most accurate method (from our own
experience) requires a fast of 12 h to be observed prior to consumption of the
lactose dose, 50 g of which is the widely accepted standard (equivalent to
approximately 1 L of cow's milk). A baseline breath hydrogen measurement
should be taken prior to the lactose dose, and at 30 min intervals afterwards
for the following 3 h (Peuhkuri, 2000). Test results for subjects with a H
2
baseline of zero (possible non-producers), or greater than 20 ppm (suggestive
of failure to fast or bacterial overgrowth of the colon), should be interpreted
with caution and followed up if possible.
6.5.
Worldwide Distribution of Lactase Persistence
A number of surveys of lactase persistence phenotype frequencies have been
carried out in many populations throughout the years, so that the global dis-
tribution of lactase persistence is now fairly well characterised (Figures 6.1a, b)
