Pre-analytical Influences on a Blood Test Study

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.

Inclusion criteria

Part 1: Effect of food intake on C4

• Healthy adult (>=18 years) volunteers from the BCPS.

Part 2: Effect of Lipid-lowering therapy on C4

• There is no patient recruitment. Spare sample collected from patients before and after starting on lipid-lowering therapy will be used.

Exclusion criteria

Part 1: Effect of food intake on serum C4

• Subjects with learning disability or those lacking mental capacity to give consent.
• Pregnant or breast-feeding
• On (prescribed and over-the-counter) medication and herbal remedies known or considered to affect lipid and bile acid metabolism.
• Chronic and acute diarrhoea
• Gastrointestinal disease.
• Previous ileal resection or cholecystectomy
• Obesity defined as a body mass index (BMI) of greater than 29.9 kg/m2

Part 2: Effect of Lipid-lowering therapy on C4

The surplus serum will not be analysed if any of the following apply to the patient:

• Pregnant or breastfeeding for either time point
• Lipid lowering therapy within the last 6 months for the first sample
• On (prescribed and over-the-counter) medication and herbal remedies known or considered to affect lipid and bile acid metabolism.
• Chronic and acute diarrhoea
• Gastrointestinal disease.
• Previous ileal resection or cholecystectomy
• Obesity defined as a body mass index (BMI) of greater than 29.9 kg/m2