14.5 Gastric Fluid, Duodenal Contents, Sputum, and Bronchoalveolar Specimens

Gastric Fluid, Duodenal Contents, Sputum, and Bronchoalveolar Specimens

The Clinical Microscopy blueprint assigns 4% to gastric and duodenal fluids, 5% to sputum, and 2% to bronchial washings. Several of the classic gastric and duodenal procedures are now rarely performed, but the board still tests their principles: how acid output is measured and interpreted, which stimulants are used, how bile fractions are collected, and how respiratory specimens are judged for quality and cellular patterns. This section covers all four specimen types.

---

1. Gastric Fluid Analysis

Collection and Physical Examination

• Patient preparation: Overnight fast (about 12 hours). Drugs that alter acid secretion (antacids, H2 blockers, proton pump inhibitors, anticholinergics) are withheld as directed by the physician.
• Collection: A nasogastric (Levin) tube is positioned in the most dependent part of the stomach, and the fasting residual is aspirated first.
• Normal fasting residual: Usually less than about 100 mL, translucent, pale gray, and slightly mucoid, with a faintly sour odor.
• Abnormal appearance: Yellow or green fluid means bile reflux from the duodenum. Brown "coffee-ground" material means old blood (hemoglobin converted to acid hematin). Bright red means fresh bleeding. A fecal odor suggests intestinal obstruction or a gastrocolic fistula.

Measuring Gastric Acidity

• Parietal cells secrete hydrochloric acid. Acid concentration is measured by titrating with 0.1 N sodium hydroxide to a pH meter endpoint of 7.0. Older methods used Töpfer's reagent (dimethylaminoazobenzene, color change near pH 3.5) for free HCl and phenolphthalein (color change near pH 8.3) for total acidity.
• Basal acid output (BAO): Four consecutive 15-minute collections over 1 hour without stimulation. Acid output (mmol/h) = acid concentration (mmol/L) × volume (L) summed across the hour.
• Maximal and peak acid output (MAO, PAO): Four 15-minute collections after a stimulant. Pentagastrin, a synthetic analog of gastrin, is the modern stimulant. Older texts list histamine, betazole (Histalog), and test meals such as Ewald's toast and tea. Insulin-induced hypoglycemia (the Hollander test) stimulates acid through the vagus nerve and was used to check whether a vagotomy was complete.
• Tubeless gastric analysis: The historical Diagnex Blue (azuresin) test gave an ion-exchange resin by mouth; gastric H+ released a dye that was absorbed and excreted in urine. Absence of dye in urine suggested achlorhydria.

Interpretation

• In Zollinger-Ellison syndrome, the tumor already drives the parietal cells near their maximum, so basal output approaches maximal output. The fasting serum gastrin is markedly high, and an intravenous secretin stimulation test produces a paradoxical rise in gastrin (secretin normally suppresses it).
• Helicobacter pylori, the main cause of peptic ulcer disease, is detected by the urea breath test, stool antigen test, or a rapid urease test on a gastric biopsy.

---

2. Duodenal Contents and Pancreatic Function

Pancreatic Secretion Tests

• A double-lumen tube allows separate gastric and duodenal aspiration so acid does not contaminate the duodenal sample.
• Secretin (or secretin-cholecystokinin) stimulation test: Secretin stimulates pancreatic ductal cells to secrete water and bicarbonate; cholecystokinin stimulates acinar enzyme secretion. Volume, bicarbonate, and enzyme output are measured in timed collections. A low peak bicarbonate concentration (normally above about 80 mmol/L) indicates chronic pancreatitis or other exocrine insufficiency.

Bile Drainage (Meltzer-Lyon Test)

• After the tube reaches the duodenum, magnesium sulfate or cholecystokinin is introduced to relax the sphincter of Oddi and contract the gallbladder. Three fractions are collected:
  1. A bile: Light golden fluid from the common bile duct.
  2. B bile: Dark olive-brown, concentrated bile from the gallbladder.
  3. C bile: Pale yellow bile flowing directly from the hepatic ducts.
• Bile is examined for cholesterol crystals and calcium bilirubinate granules (associated with gallstones), pus cells and bacteria (cholangitis), and parasites.

Duodenal Aspirate and String Test for Parasites

• Duodenal fluid can reveal Giardia duodenalis trophozoites, Strongyloides stercoralis larvae, Cryptosporidium oocysts, and the eggs of liver flukes such as Clonorchis and Fasciola.
• In the Entero-Test (string test), the patient swallows a weighted gelatin capsule containing a coiled nylon string. After about 4 hours (or overnight), the string is withdrawn, and the bile-stained mucus at its end is examined as a wet mount.

---

3. Sputum Examination

Sputum represents tracheobronchial secretions coughed up from the lower respiratory tract, distinct from saliva.

Collection and Gross Appearance

• Collection: An early-morning, deep-cough specimen is preferred, collected before eating after the patient rinses the mouth with water. When the patient cannot produce sputum, nebulized 3% hypertonic saline induces it. In the Philippine National TB Program, rapid molecular testing (such as Xpert MTB/RIF) is the primary diagnostic test, and sputum smear microscopy is used mainly to monitor treatment.
• Gross appearance:

• Dittrich plugs are small yellow-white, foul-smelling caseous masses seen in bronchiectasis and lung gangrene. Broncholiths are calcified material from old granulomas.

Specimen Quality Screening (Bartlett's & Murray-Washington Criteria)

Before performing bacterial culture or cytological stains, specimen adequacy must be confirmed under low-power field (100×) microscopy:

• Valid Sputum Specimen: Contains < 10 squamous epithelial cells (SECs) and > 25 polymorphonuclear neutrophils (PMNs) per LPF.
• Saliva Contamination (Unacceptable): Presence of > 25 SECs/LPF indicates heavy oropharyngeal contamination; the specimen must be rejected and recollected.

Characteristic Microscopic Structures in Sputum

• Curschmann's Spirals: Microscopic twisted, coiled casts of mucus plugs molded within distal bronchioles; classic finding in bronchial asthma and chronic bronchitis.
• Charcot-Leyden Crystals: Slender, elongated, diamond- or needle-shaped bipyramidal crystals formed from crystallized galectin-10 (the Charcot-Leyden crystal protein of eosinophils and basophils, formerly called lysophospholipase); hallmarked in allergic asthma and pulmonary parasitic infections (Paragonimus westermani).
• Creola Bodies: Exfoliated clusters of hyperplastic, ciliated columnar bronchial epithelial cells seen in severe reactive asthma.
• Heart Failure Cells (Siderophages): Alveolar macrophages containing engulfed hemosiderin (Prussian blue positive); seen in chronic pulmonary congestion and congestive heart failure.
• Asbestos (Ferruginous) Bodies: Golden-brown, beaded or dumbbell-shaped fibers coated with iron-protein complexes; indicative of asbestos exposure.

---

4. Bronchial Washings and Bronchoalveolar Lavage (BAL)

• Bronchial washings are aspirated during bronchoscopy from the larger airways. Bronchoalveolar lavage instills sterile saline in aliquots into a wedged lung subsegment and recovers fluid from the alveolar space. BAL samples the lower respiratory tract with little oropharyngeal contamination.
• Processing: Deliver promptly on ice or at room temperature as specified, prepare a cytocentrifuge smear for a Wright or Diff-Quik differential count, and send portions for Gram, acid-fast, and fungal stains, cultures, and cytology.
• Normal BAL differential in a nonsmoker: Alveolar macrophages more than about 85%, lymphocytes about 10% to 15%, neutrophils 3% or less, and eosinophils 1% or less. Smokers have more macrophages, many containing pigmented inclusions.

• Quantitative culture: For ventilator-associated pneumonia, growth of about 10^4 CFU/mL or more from BAL fluid is commonly taken as significant, compared with about 10^3 CFU/mL for a protected specimen brush.