CLINICAL BIOCHEMISTRY OF THE GASTROINTESTINAL SYSTEM Michaela Králíková, MD Department of Biochemistry Faculty of Medicine Masaryk University 2 major functions -digestion and absorption of food • digestion - dietary components are broken down to smaller molecules and • absorption of these digested constituents from the gut then occurs • Efficient gut motility is essential to bring about mixing and forward propulsion of the gut contents and processes leading to absorption are integrated by hormonal and neuronal mechanisms. Carbohydrate digestion and absorption • digestion starts in the mouth with the salivary a-amylase (• maldigestion —► malabsorption) Acute pancreatitis • Serum amylase • physiological value AMS /S, P < 1.67 |ikat/l • increases 5 and a number of times (100) • maximal activity within 24 - 48 h, returns within 72 hours • pancreatic koenzyme improves the diagnostic specificity - 0,2 -1 jikat/1 • activity /U < 7,67 ukat/l Acute pancreatitis • Serum 11 pase • physiologically < 1 or 3 (xkat/1 (according to methodology) • less sensitive • more specific (isn't produced by the salivary glands) • Plasma trypsin • ref. value /P ~ 272 jug/1 Chronic pancreatitis • direct tests of pancreatic function - analysis of fluid aspirated from the duodenum • secretin-cholecystokinin test • or analysis of stools • elastase • indirect tests of pancreatic f unction - assessment is made without intubation • NBT-PABAtest • fluorescein-dilaurate test • breath tests Secretin - CCK test (formerly used) secretin stimulates the pancreatic fluid secretion CCK = pancreozymin (PZ) increases the pancreatic enzymes secretion and stimulates the gall-bladder contraction assessment of total fluid volume and HC03~ amount after secretin administration assessment of pancreatic enzymes activity after administration of CCK all measured parameters are decreased in chronic pancreatitis NBT-PABA test • N-benzoyl-tyrosyl-p-aminobenzoic acid is administred with meal in order to stimulate the pancreatic secretion • NBT-PABA is split by chymotrypsin to yield PABA which is absorbed and excreted in the urine • PABA/S > 25 |Limol/l • PABA / U > 30% of administered dose Fluorescein - dilaurate test • fluorescein-dilaurate is hydrolysed by the pancreatic cholesterolesterase and fluorescein is absorbed and excreted in the urine Other tests oívancreatic function • trypsin /S after meal stimulation (j) • chymotrypsin I faeces (j) • elastase I faeces (<100 |Lig/g, ELISA, instead of SCCKT) Breath tests o í pancreatic function • given substrate cleaved by lipase, cholesterol esterase or chymotrypsin, absorbed and metabolized —► C02 • substrates used: triglycerides, cholesterol esters, acyl-Tyr-PABA • for example Triolein test = MTG test (mixed triglyceride) • measurement of C02* in breath THE SMALL INTESTINE • Tests for malabsorption of fats carbohydrates vitamin B„ Fat malabsorption • Faecal fat excretion • replaced by: • Triolein breath test = MTG test • labeled triolein (14C) is absorbed and metabolised, 14C02 is measured in breath • Serum ß-carotene • physiological value = 0,7 - 2,9 mg/1 • severe malabsorption < 0,3 mg/1 Carbohydrate malabsorption • X /lose absorption test • administration of xylose (25 g p. o., children 5 g) • assessment of xylose /S after 2 hours > 300 mg/1 1 h children > 200 mg/1 • assessment of xylose amount in 5-hour urine collection > 20% administered xyl (both adults and children) Carbohydrate malabsorption ♦ Disaccharidases deficiencies tests • enzymes within the brush border of the enterocytes: • lactase: lac —► gal + glc • saccharose: sac —► glc + fru • maltose: mal —► glc + glc • izomaltase: —> glc + glc • trehalose: tre —> glc + glc Carbohydrate malabsorption ♦ Disaccharidase deficiencies tests • administration of the given disaccharide • evaluation: a) measuring of the blood glucose response (j) • b) measuring of the faecal pH ( j) • c) breath hydrogen test (its presence in expired air is a result of the bacterial fermentation of the unabsorbed sugar) • assessment of activity of the relevant disaccharidase in biopsy tissue may be helpful Carbohydrate malabsorption ♦ Lactose load test performance • measuring of glc /P • lactose administration (50 g p. o., children older than 2 years 4 g/kg) • measuring of glc /P after 30, 60, 90,120' • next day administration of 25 g glc + 25 g gal • measuring of glc /P after 30, 60, 90,120' • in healthy pac. f glc /P more than > 1,1 mmol/1 • in deficiency lower f after lactose admin. normal f after monosaccharides admin, rate of f < 0,4 • false positive in DM and glc tolerance impairment Protein malabsorption • is not usually specifically investigated • however there are tests of protein-losing enteropathy: • i.v. administration of radio-labelled protein (51Cr, 59Fe or 131I labelled albumin, dextran or polyvinylpyrolidon) • measurement of faecal radioactivity • t if loss of proteins from the gut is present Other test of protein-losing enteropathy is: Intestinal clearance of a 1 -antitrypsin • 72 h collection of faeces (storage -4°C or -20°C) • assessment of AAT/ faeces • every day assessment of AAT /S • clearance = ' V - 0 faeces volume, ml/d S F - 0 AAT /faeces, mg/d S - 0 AAT IS, mg/d • physiologically < 35 ml/d LAMA-test • examination of intestinal permeability • administration of test solution with lactulose and mannitol • 6 h collection of urine • assessment of lactulose and mannitol /U Vitamin B12 malabsorption • Schilling test • examined in: • |B12/S • suspicion of chronic atrofic gastritis (insufficient production of intrinsic factor - IF) • suspicion of terminal ileus disease (where the complex B12-IF is absorbed) • pernicious anemia (result of j B12) Schilling test with administration of 57Co or 58Co labelled B12 measuring of *B12 /U in 24 h with and without oral administration of intrinsic factor radio-labelled B 12 CHsCÜWt HHzCOCHz HjC NhtCOCHzCHz1 CI NH^OCHz HzCHzCOf+t CK3 CK3 CHľCHľCONHz "TOI co NH H QHz e0 P h >„h7T H CHŕH HjC------CH' Schilling test without radio-labelled B 1. measuring of B12 /S 2. p.o. 1 mg B12 3. measuring of B12 /S after 4 h 4. idem with simultaneous administration of 35 mglF • ret value B12 /S = 220 -1130 ng/1 • atrofic gastritis: i after IF admin, normal • terminal ileus disease: | after IF admin. j Ľ\Dbd in stools tests [FOBT (guaiac based faecal occult blood tesť screening chemical demonstration of heme's peroxidase activity: achromatic chromogene H2A + H202 —► color chromogene A + 2 H20 cut-off of positivity = 5 mg Hb Ig stools need of bloodless diet 3 days before the test performing bleeding may be intermitent —► examination during 3 days Blood in stools tests • iFOBT f immunochemical Fecal Occult Blood Test) • immunochemical demonstration of globin • species specific —> no need of the diet • cut-off of positivity < 0,1 mg Hb /g stools