What are the Tests for Determination of Gastric Function?

The following points highlight the four main tests for the 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

1. Examination of Resting Contents
2. Fractional Gastric Analysis using Test Meals
3. Examination of Contents after Stimulation
4. Tubeless Gastric Analysis

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 the stomach:

i. Volume:

• Only 20 to 50 ml of resting contents are obtained in normal cases.
• 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.

ii. Consistency:

• The normal gastric juice is fluid in con­sistency and does not contain any food residue, and may contain small amounts of mucus.
• Food residues are present in the case of carci­noma of the stomach.

iii. Colour:

• In the case of a normal person, the gastric resi­due is clear, or it may be slightly yellow or green due to the regurgitation of bile from the duodenum.
• A dark red or brown colour may be ob­served due to the presence of altered blood or fresh blood.

iv. Bile:

Increased quantities of bile show abnormality, which is a result of intestinal obstruction or ideal stasis.

v. Blood:

• Blood is not present in normal cases.
• The presence of a small amount of fresh blood may be traumatic.
• Brown or reddish-brown blood may occur in gastric ulcers and sometimes in gastric carcinoma, due to the formation of dark brown acid haematin as a result of the hemolysis of red blood cells by HCl.
• Bleeding may also occur from gastritis.

vi. Mucous:

• A small amount of mucus may be present in normal cases.
• The increased amount of mucus is present in gastritis and gastric carcinoma. The Pres­ence of mucus is inversely proportional to the amount of HCl present.
• Swallowed saliva may contain an excess of mucus.

vii. Free and Total Oddity:

• The acidity is determined by titration with a standard solution of NaOH using methyl orange or Topfer’s reagent which indicates the endpoint by the change of red to yellow colour or using phenolphthalein indica­tor which shows the endpoint by the change of yellow to red colour.
• 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.
• The result is expressed as ml of 0.1 N HCl per 100 ml of gastric contents. This is the same as mEq/litre. This figure is obtained by multiplying the above titration by 10.
• The normal values of free acid are 0 to 30 mEq/L and that of total acid is 10 to 40 mEq/L.

viii. Organic Acids:

• The presence of large amounts of lactic acid and butyric acid in achlorhydria and hypochlorhydria indicates the remaining residual foods in the stomach. In the ab­sence of HCl, the microorganisms ferment the food residues producing lactic acid and butyric acid, (b) Achlorhydria is associated with the retention of food residues and is found in carcinoma stomach.

Fractional Gastric Analysis using Test Meals

1. Introduction of Ryle’s tube in the stomach of a fasting individual.
2. Analysis of residual gastric contents after collection.
3. Ingestion of test meal.
4. Collection of 5 to 6 ml gastric contents after a meal by aspiration using a syringe and analysis of the samples.

(i) Test Meals

• Oatmeal is prepared by adding 2 tablespoonfuls of oatmeal to one quart of boil­ing water.
• “Ewald” test meal consists of two pieces (35 gm.) of toast and 250 ml light tea.
• Either of the meal is consumed by the pa­tient and either of the tubes is introduced after one hour.

(ii) Collection of Samples:

• About 10 ml of gastric contents are collected at an interval of exactly 15 minutes through a syringe attached to the tube.
• If the stomach is not empty at the end of 3 hours, the remaining stomach contents are removed and the volume is also noted.
• Each sample is strained through a fine cloth.
• 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:

• 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 an appreciable amount of bile is also not present.
• In hyperchlorhydria, free acidity exceeds 45 mEq/litre, but the combined acidity re­mains the same as in normal persons. Hy­peracidity is found in duodenal ulcers in which a climbing type of curve is formed in gastric ulcers in which 50 per cent of cases gives normal results, and blood may be present, in gastric carcinoma in which a small percentage show hyperacidity and blood, in jejunal and gastrojejunal ulcers in which there may be hyperacidity after the operation.
• In hypochlorhydria, low acidities are found in carcinoma of the stomach and atonic dyspepsia. Free HCl is absent in gastric secretion in pernicious anaemia.
• In achlorhydria, no HCl secretion but pep­sin is present.
• In achylia gastrica, gastric secretion is completely absent due to advanced cases of cancer of the stomach, advanced cases of gastritis, and acute pernicious anaemia.

Examination of Contents after Stimulation

Alcohol Stimulation

• The Ryle’s tube is passed into the stom­ach after an overnight fast, and resting con­tents are collected for analysis.
• 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.
• The advantages of alcohol test meals are the following

(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.

• 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.

Caffeine Stimulation

• The Ryle tube is introduced into the stomach after an overnight fast and the rest­ing gastric contents are collected and ana­lysed.
• 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.
• The advantages of this stimulation are similar to that of alcohol stimulation.

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.

• Standard histamine test:

(a) The Ryle’s tube is passed into the stomach after an 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, and 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 ulcers.

• Augmented histamine test

It is a more powerful stimulus test and it shows an in­ability to secrete acid. Larger doses of his­tamine sometimes cause 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 through this period, 4 ml artisan 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 anaemia, no free HCl is secreted after histamine stimulation. In duodenal ulcers, higher values of acid are obtained.

(d) Recently, histology 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 histology is highly effec­tive in stimulating gastric secretion.

• Insulin Stimulation Test

Hypoglycemia due to insulin administration is an active stimulus of gastric acid secretion. A 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 are 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, and starch. Starch should not be present.

(iii) In duodenal ulcers, 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.

• 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 a normal person after pentagastrin stimulus varies from 20 to 40 mEq/hour.

(iv) In duodenal ulcers, the range is 15 to 83 mEq/hour. This test is of little value in gastric ulcers. 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 anaemia. 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 a peptic ulcer, gastric hy­per-secretion and diarrhoea in a patient with “gastrin”. This syndrome is also accom­panied by parathyroid adenomas with hyperparathyroidism. The secretion of pepsin occurs after stimulation with pen­tagastrin.

Tubeless Gastric Analysis

The modified test is done with the introduction of “Diagnex Blue” prepared by reacting carb acrylic cation exchange resin with “Azure A” an indicator. The hydrogen ions of the resin are exchanged with “Azur A” ions.

The reaction is reversed in the stom­ach when acid is in a concentration having a 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 a “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, and pyloric obstruction. Vitamin preparation should not be taken on the day preceding the test, which may contain substances decolourized by vitamin C.

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