Formal Ether Sedimentation stool concentration technique Principles and Procedure

formol ether sedimentation technique

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The use of concentration techniques increases the chances of identifying intestinal parasitic wether helminths or protozoans.This method increases the sensivity as compare to direct wet mount with dobell Iodine or normal saline.Among these concentration techniques,The two most commonly used stool concentration techniques are sedimentation and flotation.
The formol-ether method is a widely used sedimentation technique for stool examination.

Principle of Formal ether sedimentation technique

The Sedimentation techniques makes uses solutions of lower specific gravity as compare to the parasites, thus concentrating the latter in the sediment.

It takes advantage of the high specific gravity of protozoan cysts and helminth eggs compared to water. Their natural tendency to settle out in aqueous solutions can be accelerated by light centrifugation.

Then serving as a fixative,fixes the eggs, larvae, oocysts, and spores,hence preserves their morphology and kills but not destroy motile parasites or larva hence making it non infectious. Fecal debris is removed with the use of ethyl acetate phase of the solution leaving the Parasitic elements to freely settle at the bottom of the tube after centrifugation.

Materials required

stool sample

Glass container
Guaze
Funnel
Centrifuge tube
Centrifuge
Physiological saline (0.85% w/v Nacl)
10% buffered formalin
Ether (ethyl acetate)
Test tubes with stopper
Glass rod
Iodine
Microscope
Stool samples

Procedure for Formal Ether Sedimenation Technique

Remember to Always wear gloves when handling stool specimens.

In a suitable container, thoroughly mix a portion of stool specimen about the size of a walnut into 10mL of saline solution. Mix thoroughly.

Filter the emulsion through fine mesh gauze into a conical centrifuge tube.Centrifuge the suspension at relative centrifugal force (RCF) of 600 g (about 2000 rpm) for no less than 10 minutes. The suspension should yield about 0.75mL of sediment for fresh specimens and 0.5 mL for formalinized feces.

Decant the supernatant and wash the sediment with 10 mL of saline solution. Centrifuge again and repeat washing until supernatant is clear.

After the last wash, decant the supernatant and add 10 mL of 10% formalin to the sediment. Mix and let stand for 5 minutes to effect fixation.

Add 1 to 2 mL of ethyl acetate, Stopper the tube and shake vigorously.
Centrifuge at 450 g RCF (about 1500 rpm) for 10 minutes. Four layers should result as follow

a top layer of ethyl acetate;

plug of debris;

layer of formalin; and

sediment

Free the plug of debris from the side of the tube by ringing with an applicator stick. Carefully decant the top three layers.

With a pipette, mix the remaining sediment with the small amount or remaining fluid and transfer one drop each to a drop of saline and iodine on a glass slide.

Cover with a coverslip and examine microscopically for the presence of parasitic forms as instructed in our previous chapter below
Stool examination Direct Saline and Iodine Wet Mount Diagnosis

Observation and Results

Systematically examine the entire surface of each coverslip with the 10x objective or, if needed for identification, higher power objectives of the microscope in a systematic manner so that the entire coverslip area is observed. When organisms or suspicious objects are seen, switch to higher magnification (40X) to see more detailed morphology of the object in question.