Entero Test (String test): Principle, Procedure, Uses

Entero-Test, also known as string test or duodenal parasites test is a simple and convenient method of sampling duodenal contents/gastrointestinal fluid. The sample is examined to detect the presence of gastrointestinal parasites or any other enteric pathogens. A commercially available device that consists of a gelatin capsule containing either 90 cm (pediatric version) or 140 cm (adult version) of a highly absorbent nylon string is used for this test.

From left to right: Entero-Test device prior to swallowing, Entero-Test in situ
From left to right: Entero-Test device prior to swallowing, Entero-Test in situ (image source: Guiney WJ et al British Journal of Clinical Pharmacology)

Table of Contents


A string test involves swallowing a string with a weighted gelatin capsule, to obtain a sample from the upper part of the small intestine. The capsule is swallowed and one end of the string is taped to the side of the patient’s face. The capsule dissolves in the stomach and the string, which is weighted at its distal end, passes into the duodenum by peristalsis. Following a period of approximately 4 hr, the string and any adsorbed gastrointestinal fluid is withdrawn through the mouth.

Any Strongyloides larvae, Giardia trophozoites, or Cryptosporidium, or Cystoisospora (Isospora) oocysts that are present will also adhere to the string and will be pulled up with the string when it is removed.

Any bile, blood, or mucus attached to the string is examined under the microscope as a wet preparation for the presence of intestinal parasites (organisms/eggs) or as a permanent stained smear.

For the patient:

You may be asked not to eat or drink anything for 12 hours before the test. You may find it difficult to swallow the string, and you may feel an urge to vomit when the string is being removed.

When the test is performed?                 

Entero-Test (string test) is performed when a physician suspects a parasite infection, but no parasites were found in a stool sample. As its sensitivity is comparable to duodenal aspirate, it eliminates the need of duodenal intubation.


  1. Attach the string protruding from the capsule to the corner of the patient’s mouth.
  2. Ask the patient to swallow the capsule with water (in the stomach, gelatin capsule is dissolved and the weighted string is carried by peristalsis into the duodenum.)
  3. After approximately 4 hours, withdraw the string (during withdrawal, the small steel weight which is attached to the distal end of the string detaches and is eliminated in the stool).
  4. Remove the bile-stained mucus clinging to the string by pulling the string between thumbs and finger and collect it in a small petri dish.
  5. Examine the specimen by a wet mount technique to detect the presence of motility of the organisms or specific morphological forms (trophozoite of Giardia lamblia and larvae of Strongyloides stercoralis).
  6. Iodine may be added later to facilitate the identification of any organism present.
Trophozoite of Giardia lamblia
Trophozoite of Giardia lamblia


  • Normal test result: No presence of blood, parasites, fungus, or abnormal cells is normal.
  • Abnormal test result: Presence of giardia or another parasitic infestation.

Report the organism and stage (trophozoite, cyst, oocyst, etc.) without using abbreviations. For example Giardia lamblia (G. duodenalis, G. intestinalis) trophozoites, Strongyloides stercoralis larvae. Confirmation of some species may require a permanent stained smear.


String test is a reliable and non-invasive diagnostic method of obtaining intestinal fluid samples for the detection of Giardia lamblia and other enteric pathogens such as Cryptosporidium, Cystoisospora (Isospora).


  1. Sastry A.S. & Bhat S. (2014) Essentials of Medical Parasitology. Jaypee Brothers Medical Publishers (P) Ltd
  2. Gracia, L.S. (2016). Diagnostic Medical Parasitology. ASM Press.

Acharya Tankeshwar

Hello, thank you for visiting my blog. I am Tankeshwar Acharya. Blogging is my passion. As an asst. professor, I am teaching microbiology and immunology to medical and nursing students at PAHS, Nepal. I have been working as a microbiologist at Patan hospital for more than 10 years.

12 thoughts on “Entero Test (String test): Principle, Procedure, Uses

  1. Sir which is the best sample for antemortem rabies diagnosis? A) corneal scrapings B) skin biopsy c) saliva

    1. Several Ante-mortem test are available to diagnose Rabies infection, and no single test is sufficient. Saliva, serum, skin biopsies of hair follicle at the nape of the neck are commonly used. Among them, saliva is the preferred sample as millions of viral particles may be found intermittently in the saliva during clinical disease. Saliva is used for RT-PCR and virus isolation.

  2. Sir,regarding hepatitis B which is correct a)Ds DNA circular b) circular partial dsDNA and partial single stranded DNA

    1. Logesh Ji, Hepatitis B virus has Partial double stranded circular DNA (also known as Gapped DNA genome; one strand is complete and the other is only about half completed)

  3. Dear Tankeshwar, I came across your article in my efforts to understand if any other companies are making this Entero-test device. My name is William Guiney and you’ll note I was the lead author on the manuscript you reference above. Although intended for capturing the gut micro-flora, at GSK we have been using the devices in our clinical studies in order to study the elimination of drugs and their metabolites via the bile, however the device is not longer commercially available. The original manufacturers were HDC Corporation in the USA (Len Ross), then Neo-Medical Inc took over. Unfortunately due to illness Dr Ross failed to re-register this medical device with the FDA and subsequently its manufacture ceased. GSK and other Pharma and several research institutes would like to source this device (which has a recently expired patent) which was such invaluable as a well tolerated, minimally-invasive procedure. So, if anyone out there can manufacture a similar device or if a suitable alternative could be used I would be very grateful to have this information.

    Yours Sincerely, William Guiney

    1. Dear Sir
      Its a great pleasure and life time opportunity to get comment/information from a renowned scientist who itself has contributed for this novel discovery. I wish/hope you will find suitable Pharma/diagnostic company who want to manufacture this device. Wishing you success in this endeavor.

    2. Hello:
      Our new company (EnteroTrack LLC), started by Drs. Glenn Furuta and Steve Ackerman, who did much of the original research on the EST for esophageal sampling to evaluate esophagitis, now has the next version of the EST available for purchase. It is called the EnteroTrackerTM. Please contact me if you (or anyone else) is interested in purchasing these devices. It is currently only for research use but we will have it ready for clinical use in mid 2018.
      Robin Shandas

  4. Is entero-test still available? Not as far as I am aware…at least not for bile sampling in biomedical investiagtions in humans. Any news? Where do you order this?

  5. Found this blog recently. Our company (EnteroTrack LLC) now has the next version of the EST available for purchase for research use. The company was started by Drs. Glenn Furuta and Steve Ackerman, who did much of the original research using the EST for esophageal sampling. Please contact me (enterotrackr@gmail.com) if you would like to purchase the devices. Currently they are only available for research use.
    Robin Shandas, Ph.D.

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