Introduction

Many digestive symptoms in children, including chronic diarrhea, bloating, poor weight gain, and abdominal pain, can have causes that are difficult to identify from stool tests alone. The duodenal aspirate collection device allows a sample to be taken directly from the site where certain infections and bacterial imbalances occur, which can make diagnosis more reliable in difficult cases.

This approach matters because some organisms, such as Giardia lamblia (a microscopic parasite), are shed unevenly in stool and may be missed on a single stool examination. Similarly, bacterial overgrowth in the small intestine cannot always be confirmed through stool testing. Sampling the duodenum directly gives clinicians fluid from the exact location being investigated.

The procedure does not involve radiation. Depending on the method used, it may range from minimally invasive (a thin tube passed through the nose) to more invasive (an endoscope passed through the mouth under sedation). It is generally considered safe when performed by trained staff using age-appropriate equipment.

History of the Device

Duodenal fluid sampling has a long history in gastroenterology. Early methods in the mid-20th century relied on weighted tubes that were swallowed and allowed to pass naturally into the duodenum under gravity, with fluid then withdrawn by syringe once correct positioning was confirmed by X-ray.

In the 1960s and 1970s, a simplified device known as the string test (commercially known as the entero-test) was developed. It used a small gelatin capsule containing a coiled nylon string, with one end taped near the mouth. As the capsule dissolved in the stomach, the string unwound and passed into the duodenum, where intestinal fluid and mucus would adhere to it for later analysis. This offered a less invasive alternative to tube-based aspiration, especially useful in children and in settings with limited resources.

The introduction of flexible fiberoptic and later video endoscopes in the late 20th century added another option: aspirating duodenal fluid directly through the working channel of an endoscope during an upper gastrointestinal endoscopy. This method became attractive because it could be combined with direct visual inspection and biopsy of the duodenal lining in the same session.

Today, all three approaches, tube aspiration, the string test, and endoscopic aspiration, remain in clinical use. The choice depends on the child's age, the suspected condition, local expertise, and whether an endoscopy is already planned for another reason.

Purpose of the Device and Where It Is Used

The main purpose of duodenal aspirate collection is to obtain fluid from the upper small intestine for laboratory analysis. It is not a treatment device; it is strictly a sampling and diagnostic tool.

• Detecting Giardia lamblia trophozoites (the active, motile form of the parasite) when stool tests are negative but giardiasis is still suspected
• Quantitative bacterial culture to investigate small intestinal bacterial overgrowth (SIBO), a condition where excess bacteria accumulate in the small intestine
• Evaluating unexplained chronic diarrhea, malabsorption, bloating, or failure to thrive in children
• Research studies on the small intestinal microbial environment
• Occasionally used alongside duodenal biopsy sampling during the same endoscopic session

These devices are typically used in hospital endoscopy units, pediatric gastroenterology clinics, and specialized diagnostic laboratories. The string test version can sometimes be used in outpatient settings without sedation, though laboratory processing still requires a trained facility.

Different Types of the Device

Nasoduodenal Tube Aspiration

A thin, flexible tube is passed through the nose, down the esophagus, through the stomach, and into the duodenum. Correct positioning is confirmed before fluid is withdrawn using a syringe attached to the external end of the tube.

String Test (Entero-Test)

A gelatin capsule containing a coiled nylon string is swallowed, with the free end of the string taped outside the mouth or nose. After several hours, the string is withdrawn, and mucus adhering to it is examined for parasites. This method avoids a rigid tube and can sometimes be used without sedation.

Endoscopic Aspiration

During a standard upper gastrointestinal endoscopy, a thin suction catheter is passed through the working channel of the endoscope into the duodenum, and fluid is aspirated directly into a sterile collection trap. This method allows simultaneous visual examination and biopsy if needed.

Type	Typical Age Range	Sedation Needed	Key Feature
Nasoduodenal tube aspiration	Infants to adolescents	Usually not required	Can be done at bedside
String test (entero-test)	Older children who can cooperate	Not required	Low cost, minimally invasive
Endoscopic aspiration	Infants to adolescents (equipment size-dependent)	Usually required	Combines sampling with direct visualization

Parts and Components of the Device

Collection Tube or Catheter

A thin, flexible, biocompatible tube that guides fluid from the duodenum to an external collection point. It is sized according to the child's age and nostril or endoscope channel diameter.

Weighted Capsule and String (String Test Version)

A dissolvable gelatin capsule houses a coiled string with a small weight to help it travel through the stomach into the duodenum under normal digestive movement.

Syringe or Suction Trap

Used to gently withdraw fluid once the tube or catheter tip is confirmed to be in the duodenum. Endoscopic procedures typically use a closed suction trap connected to the endoscope's suction channel.

Sterile Specimen Container

Holds the collected fluid for transport to the laboratory. Some containers include a transport medium to preserve fragile organisms such as Giardia trophozoites, which can degrade quickly outside the body.

Guide Wire or Stylet (Tube-Based Systems)

A thin, semi-rigid wire that adds stiffness to the tube during insertion, then is withdrawn once the tube is correctly positioned.

Component	Function	Replacement Interval
Collection tube/catheter	Guides fluid from duodenum to collection point	Single-use, disposed after each procedure
Weighted capsule and string	Enables passive passage into duodenum for sampling	Single-use
Syringe/suction trap	Withdraws and holds aspirated fluid	Single-use per procedure
Specimen container	Transports sample to laboratory	Single-use per sample
Guide wire/stylet	Adds rigidity for tube placement	Single-use, disposed after insertion

How the Device Works

The basic principle is simple: a thin tube, string, or catheter is guided into the duodenum, and a small amount of the fluid naturally present there is withdrawn for examination. This fluid normally contains digestive secretions, and in affected children, it may also contain parasites or abnormal numbers of bacteria.

Correct placement is essential. For tube-based methods, position is usually confirmed by checking the fluid's appearance (duodenal fluid is typically bile-stained and yellow-green, unlike clear stomach fluid) or by imaging. For endoscopic aspiration, the tip is placed under direct camera view, so positioning is confirmed visually in real time.

Once positioned correctly, gentle suction draws a small volume of fluid into the collection system. The sample is then transferred to a sterile container, ideally within a short time window, and sent promptly to the laboratory since some organisms do not survive well outside the body.

Step-by-Step User Guide

1. Preparation and fasting: The child usually needs to fast for a set number of hours before the procedure to ensure the stomach and duodenum are relatively empty.
2. Explaining the procedure: Age-appropriate explanation and reassurance are given to the child and caregiver to reduce anxiety.
3. Positioning: The child is positioned sitting or lying on their side, depending on whether a tube or endoscope is being used.
4. Insertion: The tube, string capsule, or endoscope is gently passed through the nose or mouth toward the stomach and duodenum.
5. Confirming placement: Placement is checked by fluid appearance, imaging, or direct visualization before sampling begins.
6. Fluid aspiration: A small volume of duodenal fluid is gently withdrawn using a syringe or suction trap.
7. Removal of the device: The tube, string, or endoscope is carefully withdrawn once sampling is complete.
8. Sample labeling and transport: The specimen is labeled immediately and sent to the laboratory without delay for microscopy or culture.

Precautions and Possible Dangers

• Gagging, mild nausea, or vomiting during tube or endoscope insertion
• Minor nasal or throat discomfort, which usually resolves quickly
• Rare risk of the tube coiling in the stomach instead of reaching the duodenum, requiring repositioning
• Risks associated with sedation, when used, such as temporary drowsiness or, rarely, effects on breathing
• Very rare risk of aspiration (fluid entering the airway) if the child is uncooperative or not properly monitored
• Should be avoided or used with extra caution in children with certain bleeding disorders, severe airway problems, or unstable medical conditions unless specifically advised by the treating team

How to Keep the Device Safe and Well Maintained

• All tubes, catheters, capsules, and syringes used for duodenal aspiration are single-use and must be disposed of after each procedure according to medical waste protocols
• Reusable endoscopes used for aspiration must undergo thorough cleaning and high-level disinfection or sterilization between patients, following the manufacturer's validated reprocessing instructions
• Suction equipment should be checked and calibrated regularly to ensure gentle, controlled fluid withdrawal
• Specimen containers and transport media should be stored according to the manufacturer's temperature and expiry guidelines
• Laboratory data management systems used to log and track samples should have secure backup procedures
• Software used for endoscopy documentation should be kept updated per the manufacturer's recommendations

Interactive Tool: Procedure Readiness Checklist

Interactive FAQ

Other Methods and Alternatives

Method	Basic Principle	Common Use
Duodenal aspirate collection	Direct sampling of fluid from the duodenum for microscopy or culture	Confirming giardiasis or bacterial overgrowth after inconclusive simpler tests
Stool antigen/PCR test	Detects parasite proteins or genetic material in stool	First-line, non-invasive screening for giardiasis
Hydrogen/methane breath test	Measures gases produced by intestinal bacteria after a sugar substrate is ingested	Non-invasive screening for suspected bacterial overgrowth
Small bowel biopsy	Direct tissue sampling during endoscopy for microscopic examination	Evaluating structural or inflammatory small bowel disease alongside aspirate findings
Stool microscopy (ova and parasite exam)	Direct visual search for parasites or eggs in stool	Initial, repeatable, low-cost parasite screening

Frequently Overlooked Points Worth Knowing

• A single negative stool test does not fully exclude giardiasis, since the parasite can be shed intermittently
• Duodenal fluid samples for Giardia should be examined promptly, as trophozoites can lose their motility and become harder to identify if the sample sits too long
• Bacterial overgrowth culture thresholds have been debated among specialists, and newer proximal small bowel cutoffs differ from older duodenal aspirate cutoffs
• A single sampling point may not represent bacterial populations throughout the entire small intestine
• Recent antibiotic use before the procedure can affect both giardia detection and bacterial culture results
• Combining aspiration with biopsy during the same endoscopy can add diagnostic value without a separate procedure

How to Read and Understand the Results

Result Parameter	What It Means
Giardia trophozoites/cysts present	Suggests active giardiasis infection; correlated with symptoms for diagnosis
Giardia not identified	Reduces likelihood of giardiasis at the time of sampling but does not completely rule it out
Bacterial colony count below threshold	Generally considered within a normal range for small intestinal bacterial population
Bacterial colony count above threshold	Suggestive of small intestinal bacterial overgrowth, interpreted alongside symptoms

Advantages and Limitations

Advantages

• Samples fluid directly from the site of suspected infection or bacterial imbalance
• Can detect cases missed by stool testing alone
• Can be combined with endoscopic visualization and biopsy in one session
• No radiation exposure involved

Limitations

• More invasive than stool or breath testing
• Requires trained personnel and, often, a hospital or endoscopy unit setting
• A single sample may not reflect variation throughout the small intestine
• Sedation-related risks apply to endoscopic methods
• Sample must be processed quickly to preserve fragile organisms

Troubleshooting Common Problems

Problem	Possible Cause	Suggested Solution
Tube fails to reach the duodenum	Coiling in the stomach or incorrect insertion technique	Reposition the child, adjust technique, or confirm placement with imaging before reattempting
Insufficient fluid aspirated	Prolonged fasting, tube tip against the bowel wall, or thick secretions	Reposition the tube slightly, flush gently, or attempt aspiration at a slightly different depth
Sample degrades before laboratory analysis	Delayed transport or improper storage temperature	Transport promptly in the correct container and notify the laboratory in advance
Child unable to tolerate tube insertion	Anxiety, strong gag reflex, or lack of cooperation	Use topical numbing, distraction techniques, or consider sedation/endoscopic approach instead
Inconsistent bacterial culture results	Contamination during collection or variability in laboratory technique	Follow strict sterile collection technique and use a laboratory experienced in quantitative duodenal cultures

When to Contact the Manufacturer or Service Provider

• If a reusable endoscope or accessory shows visible damage, malfunction, or difficulty passing fluid through the suction channel
• If specimen containers or transport media appear discolored, damaged, or past their expiry date
• If sterilization or reprocessing equipment used for endoscopic accessories shows error codes or inconsistent cycle results
• If replacement parts, such as suction traps or specialized catheters, are needed for restocking

Suggested Reading and Official Resources

Readers who want to learn more can refer to the following types of official and academic sources:

• Pediatric gastroenterology textbook chapters covering giardiasis and small intestinal bacterial overgrowth
• Peer-reviewed journal articles on duodenal aspirate culture techniques and diagnostic thresholds
• World Health Organization resources on giardiasis and intestinal parasitic infections
• Manufacturer instructions for use for nasoduodenal aspiration kits and string test devices
• Clinical practice guidelines from pediatric gastroenterology and infectious disease specialty societies