Measurement of gastric acid secretion



Parietal cells of the gastric mucosa produce hydrochloric acid at a concentration of about 0.5 mmol/l. The source of the hydrogen ion H+ is water, which is dissociated by membrane hydrolysis in conjunction with the carbonic anhydrase reaction producing CO2. Carbonic anhydrase is a limiting factor for HCl production in the gastric mucosa. Regulation of gastric secretion is controlled by neurohumoral mechanisms, a significant factor is the level of gastrin. Investigation of gastric acidity is based on stimulation of parietal cells, collection of gastric juice, and determination of free and total HCl content. Pentagastrin is the most suitable for stimulation, histamine (Lambling's test) or insulin can also be used. However, the evaluation of the functional test depends on the type of stimulation, ie the result differs after the administration of gastrin, histamine, or insulin.

Test Procedure
The patient arrives on an empty stomach and has a gastric tube, the position of which must be verified by sciascopy. The gastric contents are pumped out using a suction pump and the individual portions are collected after 15 minutes, for a total of 2 hours. First, all gastric juice is taken on an empty stomach - portion T0 – and then followed by the collection of unstimulated, basal secretion T60 4 × 15 minutes. After 1 hour of the test, 6 µg pentagastrin/kg body weight is stimulated subcutaneously (histamine is administered as a 1% solution at a dose of 0.1 ml/10 kg body weight, insulin is also administered at 10–20 IU NI). This is followed by another 4 servings after 15 minutes - stimulated T120 secretion.

Laboratory analysis
We measure pH volume and titrate HCl concentration in all portions. Titrate 10 ml (minimum 5 ml) of gastric juice with 0.1 mol/l NaOH in the presence of a colored pH indicator (eg diethylaminoazobenzene). Determine the HCl concentration in each fraction, calculate the total HCl output and the secretion rate mmol HCl/hour. The indices used in the diagnosis are designated BAO (Basal acid output), determined from the basal fraction T60 before stimulation; PAO (Peak acid output) determined by the average of the two fractions with the highest concentration of HCl and MAO (Maximum acid output) as a result of hourly stimulated T120 secretion. Pepsin concentrations such as BPO (Basal pepsin output) and MPO (Maximal pepsin output) are also determined in the insulin test.

Pentagastrin test reference values: BAO 1–5 mmol HCl/hr, MAO 10–23 mmol HCl/hr, PAO 8–40 mmol HCl/hr. Values ​​in men are higher than in women (PAO in men is 11–40, in women 8–33 mmol HCl/hr). After stimulation with histamine, we evaluate the total volume of gastric juice, normal values ​​are 150–250 ml/2 hours and total acidity 72–80 mmol HCl/l. Insulin test values ​​in men are BPO 32 ± 29 mg/hod, MPO 320 ± 170 mg/hour; in women BPO 60 ± 81 mg/hour, MPO 170 ± 150 mg/hour.

The clinical significance
Hypochlorhydria (hypoacidity) to achlorhydria (anacidity) is a significant symptom of pernicious anemia, suspected malignancies (however, gastric cancer shows hyperacidity and normoacidity in the early stages). The determination of gastric acidity in Zollinger-Ellison syndrome, is diagnostically important, when we demonstrate high basal and maximal secretion (BAO > 15 mmol/hour, MAO > 60 mmol/hour), in more than 50 % of cases of Zollinger-Ellison syndrome the BAO/MAO index is > 0.60. Pentagastrin stimulation of the test is also applicable for mucin analysis. Recent studies use the bQRT test (Blood Quininium Resin Test) to determine hypochlorhydria.

Endoscopic function test variants
Stimulation is performed with 4 μg tetragastrin/kg body weight subcutaneously, a 10-minute secretion is collected by an endoscopic probe (20–30 min after stimulation) and acidity is determined by titration in mmol/10 min. The correlation with MAO-BAO is r = 0.92, CV reproducibility = 5.6 %.

Source

 * with the permission of the author taken from KOCNA, Petr. GastroLab: MiniEncyclopedia of laboratory methods in gastroenterology  [online]. © 2002. Last revision 2011-01-08, [cit. 2011-03-04]. < http://www1.lf1.cuni.cz/~kocna/glab/glency1.htm >.