Pre-analytical Influences on a Blood Test Study

Overview

Chronic diarrhoea is common and often believed to result from irritable bowel syndrome (IBS). However, up to 50% of patients with an IBS diagnosis may have something called Bile Acid Diarrhoea (BAD) instead. BAD is easily treatable however diagnosis currently relies on a complex test involving two full body scans. The aim of the study is therefore to investigate whether a simple laboratory test, that can be done on a single blood sample, would be appropriate instead. This laboratory test is called 7aC4. In order to determine whether 7aC4 could be a good test for BAD, it needs to be determined whether eating a meal can alter the levels of 7aC4. The aim of this study is to measure 7aC4 at several time points before and after eating a meal, to see what effect this has on 7aC4 levels.

Chronic diarrhoea is common and largely due to irritable bowel syndrome (IBS). IBS is reported to affect about 11% of the UK population. About half these patients are believed, however, to have bile acid diarrhoea (BAD). There are, therefore, more than one million patients with BAD in the UK. BAD is caused by small bowel malabsorption of bile acids (BA) and increased BA in the large intestine cause diarrhoea. Once diagnosed, the treatment of BAD is simple and effective. BAD, however, is often not diagnosed because of a lack of easily available and reliable diagnostic methods. In the UK, the radiolabelled 23-seleno-25-homotaurocholic acid test (SeHCAT) is the gold-standard diagnostic method. The SeHCAT is performed by oral administration of a radiolabel, followed by two full-body scans, one week apart, to assess retention of BA. A low retention time indicates BAD. SeHCAT, however, is expensive, inconvenient to the patient, exposes the patient to radiation and has limited availability. A simple laboratory biomarker for the diagnosis of BAD is, therefore, desirable. Proposed diagnostic laboratory biomarkers for BAD include measurement of faecal BA and serum 7a-hydroxy-4-cholesten-3-one (C4). C4, an intermediate in the BA synthesis pathway, is the common precursor for the primary BAs. It is, therefore, utilised as a biomarker of BA synthesis. Serum C4 increases in BAD, as BA synthesis increases to compensate for the increased faecal BA loss. C4 measurement requires a single serum sample for analysis by liquid chromatography tandem mass spectrometry (LC-MS/MS). There is, however, limited data comparing its diagnostic accuracy to the SeHCAT scan. Furthermore, pre-analytical variables which may affect C4, include cholesterol lowering medication, diurnal variation and effects of food intake require clarification to optimise conditions for sample collection before its introduction into routine laboratory use. Literature suggests both diurnal variation and post-prandial response can influence C4 levels, however there is limited information on whether this is primarily a post-prandial response, or due to diurnal variation. This study aims to compare pre- and post-prandial C4 levels, controlled for diurnal variation.