The following points highlight the four main tests for determination of gastric function. The tests are: 1. Examination of Resting Contents 2. Fractional Gastric Analysis using Test Meals 3. Examination of Contents after Stimulation 4. Tubeless Gastric Analysis.
Tests for Determining Gastric Function:
- Examination of Resting Contents
- Fractional Gastric Analysis using Test Meals
- Examination of Contents after Stimulation
- Tubeless Gastric Analysis
Test # 1. Examination of Resting Contents:
After a night’s fast the stomach contents are completely removed by passing the tube.
The following characteristics are important in the diagnosis of diseases of stomach:
(a) Only 20 to 50 ml of resting contents are obtained in normal cases.
(b) An increase in volume may be due to hyper-secretion of gastric juice, retention of gastric contents owing to delayed emptying of the stomach, and regurgitation of the duodenal contents.
(a) The normal gastric juice is fluid in consistency and does not contain any food residue and may contain small amounts of mucus.
(b) Food residues are present in case of carcinoma of the stomach.
(a) In case of normal person, the gastric residue is clear or it may slightly yellow or green due to regurgitation of bile from duodenum.
(b) A dark red or brown colour may be observed due to the presence of altered blood or fresh-blood.
Increased quantities of bile shows abnormality which is a result of intestinal obstruction or ideal stasis.
(a) Blood is not present in normal cases.
(b) Presence of small amount of fresh blood may be traumatic.
(c) Brown or reddish-brown blood may occur in gastric ulcer and sometimes in gastric carcinoma due to the formation of dark brown acid hematin as a result of the hemolysis of red blood cells by HCl.
(d) Bleeding may also occur from gastritis.
(a) A small amount of mucus may be present in normal cases.
(b) Increased amount of mucus is present in gastritis and in gastric carcinoma. Presence of mucus is inversely proportional to the amount of HCl present.
(c) Swallowed saliva may contain excess of mucus.
vii. Free and Total Oddity:
(a) The acidity is determined by titration with a standard solution of NaOH using methyl orange or Topfer’s reagent which indicates end point by the change of red to yellow colour or using phenolphthalein indicator which shows end point by the change of yellow to red colour.
(b) The presence of the amount of free HCl is free acidity; the complete titration shows the total acidity which is composed of protein hydrochloride and any organic acid; the difference between two titrations gives the combined acid.
(c) The result is expressed as ml of 0.1 N HCl per 100 ml of gastric contents. This is same as mEq/litre. This figure is obtained by multiplying the above titration by 10.
(d) The normal values of free acid is 0 to 30 mEq/L and that of total acid is 10 to 40 mEq/L.
viii. Organic Acids:
(a) The presence of large amounts of lactic acid and butyric acid in achlorhydria and hypochlorhydria indicates the remaining of residual foods in the stomach. In absence of HCl, the microorganisms ferment the food residues producing lactic acid and butyric acid, (b) Achlorhydria is associated with retention of food residues and is found in carcinoma stomach.
Test # 2. Fractional Gastric Analysis using Test Meals:
This consists of:
i. Introduction of Ryle’s tube in stomach of a fasting individual.
ii. Analysis of residual gastric contents after collection.
iii. Ingestion of test meal.
iv. Collection of 5 to 6 ml gastric contents after meal by aspiration using a syringe and analysis of the samples.
(i) Test Meals:
(a) Oatmeal is prepared by adding 2 tablespoonful’s of oat meal to one quart of boiling water.
(b) “Ewald” test meal consists of two pieces (35 gm.) of toast and 250 ml light tea.
(c) Either of the meal is consumed by the patient and either of the tubes in introduced after one hour.
(ii) Collection of Samples:
(a) About 10 ml gastric contents are collected at an interval of exactly 15 minutes by means of syringe attached to the tube.
(b) If the stomach is not empty at the end of 3 hours, the remaining stomach contents are removed and the volume is also noted.
(c) Each sample is strained through a fine cloth.
(d) The strained samples are analysed for free and total acidity and the residue on the cloth is examined for mucus, bile, blood, and starch.
(iii) Results and Interpretation:
(a) In normal health, after taking the meal, the free acid is found after 15 to 45 minutes (See figure below). The free acid then steadily rises to reach the maximum at about 15 minutes to 1/2 hour, after which the concentration of free acid begins to fall. The free acid ranges from 15 to 45 mEq/litre at the maximum with total acid at about 10 units higher. Blood is not present and appreciable amount of bile is also not present.
(b) In hyperchlorhydria, free acidity exceeds 45 mEq/litre but the combined acidity remains the same as in normal persons. Hyperacidity is found in duodenal ulcer in which a climbing type of curve is formed in gastric ulcer in which 50 per cent cases give normal results, and blood may be present, in gastric carcinoma in which small percentage show hyperacidity and blood, in jejunal and gastrojejunal ulcers in which there may be hyperacidity after operation.
(c) In hypochlorhydria, low acidities are found in carcinoma of stomach and in atonic dyspepsia. Free HCl is absent in gastric secretion in pernicious anemia.
(d) In achlorhydria, no HCl secretion but pepsin is present.
(e) In achylia gastrica, gastric secretion is completely absent due to advanced cases of cancer of stomach, advanced cases of gastritis, and acute pernicious anemia.
Test # 3. Examination of Contents after Stimulation:
A. Alcohol Stimulation:
(i) The Ryle’s tube is passed into the stomach after overnight fast and resting contents are collected for analysis.
(ii) 100 ml of 7 per cent ethyl alcohol is administered. Samples of gastric contents are collected at an interval of 15 minutes and all the samples are analysed for free and total acidity, peptic activity, presence of bile, blood and mucus.
(iii) The advantages of alcohol test meal are the followings:
(a) More easily administered and prepared.
(b) Consumed better.
(c) The gastric response is more rapid and more intense.
(d) Quick emptying of the stomach.
(e) Specimens are clear and easily analysed.
(iv) The disadvantages of this test are:
(a) Stimulus with alcohol is more vigorous.
(b) Stimulus is not so strictly physiological.
(c) Free acidity levels are higher and normal limits are wider.
(i) The Ryle’s tube is introduced into the stomach after overnight fast and the resting gastric contents are collected and analysed.
(ii) Caffeine sodium benzoate (500 mg dissolved in 200 ml of water) is administered
orally. Samples of stomach contents are collected at an interval of 15 minutes and analysed for free and total acidity, peptic activity, presence of bile, blood and mucus.
(iii) Advantages of this stimulation is similar to that of alcohol stimulation.
C. Histamine Stimulation test:
Histamine is a powerful stimulant for the secretion of HCl in the normal stomach. It increases the cAMP level which causes the increased secretion of highly acidic gastric juice with low pepsin content.
(i) Standard histamine test:
(a) The Ryle’s tube is passed into the stomach after overnight fast and the stomach contents are collected for analysis.
(b) A subcutaneous injection of histamine (0.01 mg/kg body weight) is inserted. 10 ml stomach contents are collected at an interval of 10 minutes for one hour and samples are analysed for free and total acidity, peptic activity, presence of bile, blood and mucus.
(c) Achylia gastrica (“true” achlorhydria) is indicated by the absence of free HCl in the secretion after histamine administration. More juice may be secreted in duodenal ulcer.
(ii) Augmented histamine test:
It is a more powerful stimulus test and it shows an inability to secrete acid. Larger doses of histamine sometimes causes an unwanted severe reactions.
(a) The Ryle’s tube is introduced after an overnight fast and the gastric contents are collected for analysis. The resting contents are collected at an interval of 20 minutes for an hour. Halfway of this period, 4 ml anthisan is given intramuscularly.
(b) At the end of the hour, histamine (0.04 mg histamine acid phosphate per kg body weight) is given subcutaneously and gastric contents are collected at an interval of 15 minutes for one hour for analysis.
(c) In pernicious anemia, no free HCl is secreted after histamine stimulation. In duodenal ulcers, higher values of acid are obtained.
(d) Recently, histalog is used in place of histamine. No side effects like histamine are observed by its use. The recommended dose of histamine is 10 to 50 mg. This histalog is highly effective in stimulating gastric secretion.
D. Insulin Stimulation Test:
Hypoglycemia due to insulin administration is an active stimulus of gastric acid secretion. The blood sugar level below 45 mg per cent is essential for a reliable test.
(i) The Ryle’s tube is passed into the stomach after an overnight fast and the stomach is made empty.
(ii) 15 units of soluble insulin is injected intravenously and about 10 ml gastric contents are collected at an interval of 15 minutes for 2 ½ hours. The samples are analysed for free and total acidity, peptic activity, and presence of blood, bile, starch. Starch should not be present.
(iii) In duodenal ulcer, acid level is more in response to insulin. The concentration of free acid may be over 100 mEq/litre. After vagotomy no response of insulin is found and the gastric acidity remains at 15 to 20 mEq/litre before and after insulin injection.
E. Pentagastrin Test:
Pentagastrin is a synthetic peptide and it is butyl-oxy-carbonyl β-alanine. It is an active stimulator.
(i) The Ryle’s tube is passed into the stomach after an overnight fast and the resting contents are completely removed. After emptying the stomach two 15 minute specimens are collected to have the “basal secretion”.
(ii) Pentagastrin (6µg/kg body weight) is injected subcutaneously and specimens are collected at an interval of 15 minutes for analysis.
(iii) The normal basal secretion rate is 1 to 2.5 mEq/hour. The maximum secretion in normal person after pentagastrin stimulus varies from 20 to 40 mEq/hour.
(iv) In duodenal ulcer, the range is 15 to 83 mEq/hour. This test is of little value in gastric ulcer. The “true” achlorhydria is found in cancer of the stomach. The reduced acid level is observed in acute gastritis. The “true” achlorhydria is also noted in Pernicious anemia. The Zollinger- Ellison syndrome is characterised by a high basal secretion usually above 10 mEq/hour and no further rise is found after giving Pentagastrin.
This syndrome is characterised by peptic ulcer, gastric hyper-secretion and diarrhoea in patient with “gastrin”. This syndrome is also accompanied by parathyroid adenomas with hyperparathyroidism. The secretion of pepsin occurs after stimulation with pentagastrin.
Test # 4. Tubeless Gastric Analysis:
The modified test is done with the introduction of “DiagnexBlue” prepared by reacting carbacrylic cation exchange resin with “Azure A” an indicator. The hydrogen ions of the resin is exchanged with “Azur A” ions.
The reaction is reversed in the stomach when acid is in a concentration having pH less than 3.0. The indicator “Azur A” is released by the action of acid. The released one is absorbed in the small intestine and excreted in the urine, the colour of which is matched with known standards.
This test is valuable if it is used as “screening test” only. A positive result indicates the secretion of acid by the stomach. A negative result is an unreliable indicator of “true” achlorhydria.
This test is not reliable in patients suffering from renal diseases, urinary retention, malabsorption, pyloric obstruction. Vitamin preparation should not be taken on the day proceeding the test which may contain substances decolorized by vitamin C.