LABORATORY EVALUATION OF GIT DISEASE
Laboratory evaluation in GIT disorders depend on the suspected etiology, though some important investigations are as follows:
I. Stool examination is the baseline investigation for suspected GIT disease.
A freshly collected sample should be examined for:• Gross characteristics, which vary according to the age and dietary pattern. Older children on home diet usually pass well-formed stools, which are brownish due to bile pigment and slightly foul smelling due to presence of indole and skatole - degradation products of organic matter.
Gross stool examination includes evaluation of its: (a) bulk, (b) consistency, (c) color, (d) odor, and (e) presence of unusual substances, e.g. blood, mucus or worms.
Some important diagnostic clues are as follows:
- Clay-colored stools indicate obstructive jaundice, while black-tarry stools may be due to melena or after iron administration.
- Rice-water stools indicate cholera or ETEC diarrhea.
- Hard stools with pellet or ribbon-like appearance indicate Hirschsprung disease.
- Bulky, pale, extremely foul-smelling stools with fat-globules indicate fat malabsorption (steatorrhea).
- Frothy, explosive and watery stools indicate lactose intolerance.
- Presence of blood indicates dysentery or GIT bleeding.
• Biochemical examination commonly includes: (a) pH estimation, (b) Benedict test and (c) Benzidine test.
Fig. 14.2: Common ova and cysts on stool microscopy.
(A) E. histolytica (trophozoites); (B) E. histolytica (cysts); (C) G. Iamblia (trophozoites); (D) G. Iamblia (cysts); (E) Ascaris Iumbricoidis (fertilized egg); (F) Ascaris lumbricoidis (unfertilized egg); (G) Ankylostoma duodenale (egg); (H) Enterobius vermicularis (egg); (I) H. nana (egg); (J) T. trichuria (egg).
- Normal stool pH is alkaline, estimated by dipping a pH paper in stool suspension (red turns blue). Acidic stools (blue turns red) indicate lactose intolerance.
- Benedict test detects presence of reducing sugar in stools, e.g. in disaccharide intolerance, performed in similar manner as for urine, except the use of a stool-saline suspension instead of urine sample (Ch 21.2).
- Benzidine test detects presence of occult blood in stools, e.g. in hookworm infestations, performed in similar manner as for urine, except the use of a stool-saline suspension (Ch 21.2).
• Microscopic examination: An unstained slide of saline stool suspension should be examined for-(a) cellular elements, e.g. RBCs or pus cells, (b) ova/ cysts of protozoa and parasites (Fig. 14.2). Iodine staining for nuclear structures is commonly used to differentiate organic from inorganic matter.
Hanging-drop preparation is essential in rice-water diarrhoea to exclude cholera. A drop of fresh stool sample is placed on cover-slip, which is then inverted on a slide to see darting motility of V. cholerae on microscopy.
II. Radioimaging studies: The choice of radioimaging depends on the suspected etiology, though common methods include:
• Plain X-rays are of limited use in GIT evaluation due to presence of gases and limited air-tissue contrast. However, an erect X-ray is essential in acute abdomen and must be evaluated for: (a) multiple air-fluid levels* in intestinal obstruction, (b) gas under diaphragm in intestinal perforation, extra-abdominal soft tissue,
(c) lower lung abnormalities in basal pneumonitis/ pleuritis, (d) foreign bodies and other obvious lesions, e.g. musculoskeletal deformities.
*Up to three air-fluid levels are normal in standing X-ray abdomen, denoting interface at stomach, ileocaecal region and sigmoid colon. More than gt;3 levels indicates paralytic ileus or mechanical intestinal obstruction.
• Barium studies are more useful to delineate structural abnormalities and include: (a) barium swallow for suspected esophageal pathology, (b) barium meal for suspected gastric pathology, (c) barium meal with follow- through for small intestinal lesions, and (d) barium enema for colonic lesions.
• Ultrasonography is the preferred base-line investigation for evaluation of almost all abdominal pathologies including visceral masses, ascites and even unexplained presentations. CT/MRI is indicated only in selected cases to supplement USG findings.
III. Endoscopy is being increasing used for various diagnostic and therapeutic procedures in children with suspected GIT disorders (Table 14.1). While upper GI endoscopy provides an opportunity to visualize from esophagus till duodenum and proximal jejunum, colonoscopy is used to reach pathologies from anal canal till distal ileum through ileocaecal valve.
14.4