The patient's expectation during H2 breath testing: Don’t underestimate the reader's expectation
Article Outline
Sir,
We read with interest the paper by Vernia et al. [1], suggesting that a “nocebo” effect due to lactose administration may cause a false positivity for lactose intolerance. As the Authors correctly reported, it is known that the patient's expectations may be linked to a psycho-emotional mechanism inducing the onset of symptoms after placebo or food and side effects after drug administration. Anxiety, depression and somatisation were shown to have a role in the pathophysiology of the nocebo effect. The paper by Vernia et al. shows that, independently of H2 breath test results, a subgroup of patients, already tested for lactose malabsorption with lactose breath test, develop abdominal symptoms during a further breath test which foresees the administration of a solution containing 1
g of glucose, a dose unable to increase breath H2 excretion. Three main criticisms must be raised. First, it is important to know whether the subgroup of patients showing such a symptomatic response after placebo was characterised by an increased prevalence or higher severity of anxiety, depression or somatisation compared to the large group of subjects who did not show any symptoms. In a recent survey, the prevalence of somatisation disorder was diagnosed in 30% of patients with IBS and was associated with significantly greater numbers of both gastrointestinal and non-gastrointestinal symptoms, but also with physician visits, telephone calls to physicians, urgent care visits and missed work days [2]. Consequently, an increased prevalence of psychiatric illness in this subgroup might also explain the acceptance of a further diagnostic evaluation, making the selected group unreliable to draw the Authors’ conclusions. Second, the study did not follow a double-blind design, which is the only study design considered accurate for the aim of these studies.
What we consider the major criticism to the paper is represented by the protocol used for the lactose breath test: a 4-h lactose breath test was shown to be characterised by a very low sensitivity both in vivo [3] and in vitro [4]. A better sensitivity can be achieved by prolonging breath H2 monitoring up to 6 (76%) or 7h (81%) [3], [4]. Accordingly, to perform an accurate evaluation of the relationship between symptom occurrence and lactose malabsorption, the adoption of the most accurate protocol is mandatory. An inaccurate protocol cannot exactly separate lactose absorbers and lactose malabsorbers and, therefore, accurately define the relationship between intolerance symptom onset and both lactose and placebo/glucose intake.
It could be argued that the protocol used by the Authors was recommended by a recent survey on methodology of the H2 breath test in gastrointestinal disorders [5]. However, we feel that the statements produced by this consensus conference on the diagnosis of lactose malabsorption are prone to several criticisms: the systematic review of the literature performed by the section Authors was largely incomplete; papers were misquoted [3]; data evaluating in vivo [3] and in vitro [4] accuracy were not considered. Consequently, a mere quantitative, rather than qualitative, evaluation of papers on this topic was in fact performed.
In conclusion, even if the nocebo effect may have a role during a lactose tolerance test, the paper by Vernia has methodological shortcomings. The Authors have been involved in H2 breath test studies for a long time and an awareness of the pitfalls causing a low accuracy of this diagnostic tool is expected. Only an accurate test protocol could offer important insight on this topic and we expected such a protocol from these Authors. We think that while the patient's expectation is a very important point, the reader's expectation should also be considered!
References
- Diagnosis of lactose intolerance and the “nocebo” effect: the role of negative expectations. Dig Liver Dis. 2010;43:86
- The presentation of irritable bowel syndrome in the context of somatization disorder. Clin Gastroenterol Hepatol. 2004;2:787–795
- Hydrogen breath test in the diagnosis of lactose malabsorption: accuracy of new versus conventional criteria. J Lab Clin Med. 2004;144:313–318
- Detection of low doses of carbohydrate: accuracy of various breath H2 criteria. Gastroenterology. 1993;105:1404–1410
- H2-breath testing for carbohydrate malabsorption. Aliment Pharmacol Ther. 2009;29(Suppl. 1):14–18
PII: S1590-8658(10)00209-4
doi:10.1016/j.dld.2010.06.003
© 2010 Editrice Gastroenterologica Italiana S.r.l. Published by Elsevier Inc All rights reserved.
