Food intolerance can be an important factor in many acute and chronic conditions, producing delayed onset symptoms ranging from IBS, muscle and joint aches, fatigue, weight problems, hyperactivity, skin irritations and anxiety. The FACTest measures all types of immunological reactions to a total of 233 different foods, including common  seasonings, colourings, additives and beverages from a single blood sample.

A drink containing PEG 400, a mixture of eleven sizes of molecules, is taken. The different sizes of molecules pass through the gut wall and into the circulation with differing levels of ease. All the urine passed over the next six hours is collected. The quantity of each molecular size of PEG in the urine collection are measured and we can then reconstruct an absorption profile.

The patient is given 1 gramme of glucose in hardened gelatine capsules (2 x 500mg capsules) with 4 grammes of glucose dissolved in 80-100ml of water. The glucose solution prevents the capsules from disintegrating in the stomach and this ensures that an adequate amount of glucose passes into the duodenum. A blood sample is taken one hour later and the plasma is analysed for simple and complex alcohols along with short chain fatty acids. Comments are added when abnormalities of bacterial fermentation or a possible yeast overgrowth are indicated by the results.