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Stool examination methods are important for patient diagnosis. It is consists of undigested food, dead bacteria, and mucosa. Feces ( stool ) also contain excretory substances which excreted from bile into the intestine. The gut is the most contaminated viscera in the body
Collection of stool specimen
The stool can be collected by a bedpan. Care should be taken, to prevent mixing of stool with urine. From bed_pan suitable amount transferred to the appropriate container like a cardboard box. The stool specimen should be 4ml in quantity.
Note: while collecting stool, care should be taken, actual abnormal parts should be transformed to the laboratory within one hour. It is important when the vegetative form of amoeba is to be seen.
Types of stool examination methods
- Physical Examination of Stool
- Microscopic Examination of Stool
- Blood test
Pysical Examination of Stool Examination
Physical examination of stool consists of the following test.
- Colour of the stool: Normal colour of stool is due to stercobilinogen. This stercobilinogen is synthesised by the bacteria by the decomposition of bilirubin. In the presence of air, it converts into stercobilin. In the infant, there are no bacteria, therefore infant stool lack setercobilinoge. Bleeding of upper track of intestine or gut result in black stool but if bleeding on lower track results in Red stool or Feaces. Note. iron supplements also result in black stool.
- Odour: Normally stool odour is due to indole and skatole. It also depends on PH and bacterial fermentation.
- Consistency: Normally faeces are formed or semi-formed. liquid or semi-liquid, solid or semi-solid. All of these are due to some causes. In constipation, hard faeces are excreted while in diarrhoeal stool mixed with blood and mucus. Most often blood in stool is due to amoebic dysentery. Watery faeces are seen in cholera.
- PH reaction: Normal PH of stool is either neutral or slightly alkaline. Carbohydrate change the PH into acid, protein breakdown change PH into alkaline (bacillary dysentery)
Microscopic Examination of Stool
Stool are exaimend by two method.
- Direct Wet Preparation
- Concentration Technique
Direct Wet Preparation
In this method, the suspension is prepared by mixing stool with normal saline. after this one drop of Lugol iodine drop on slid. Cover the slid with a coverslip. We can see RBC, WBC, Starch, Ova, motile amoeba
Lugol iodine is given good contrast and stains some types of cysts. The stool also contains hair, vegetables, starch yeast.
Concentration technique is used when egg or parasite are not seen by wet method but their symptoms exist. It has the following methods.
- Formalin Ether sedimentation
- Sodium chloride Floatation method
- Zinc Sulphate Floatation method
Formalin Ether Sedimentation
This method is easy to use but important because formaline not only kill the parasites but also fix their body for microscopic study.
Sodium Chloride Flotation method
In this method, the stool is mixed with a saturated solution of Sodium Chloride (NaCl). Eggs of parasites are lighter in weight so they float on the surface.
Zinc Sulphate Floatation method
This method is specific for parasites cyst and some helminth. They rise to the top of surface due to the specific gravity of liquid-like Zinc Sulphate (1:180 ) due to their buoyant properties in liquid.
Blood in stool can be check by two methods.
- Benzidine test
- Orthotoludine test
In this method, microscopic blood detected in stool. More than 10 ml of blood gives black colour to stool. if blood is less than 10 ml then the benzidine method is used. Peroxidase in the heam portion of hemoglobin expels oxygen from hydrogen peroxide. This oxygen oxidizes the benzidine acidic medium into a blue color medium.
In this method, Orthotiludine change into blue color compound in the presence of blood.