The string test, also known as the Entero-Test, is a diagnostic procedure primarily used to detect intestinal parasites like Giardia lamblia (or Giardia duodenalis) by collecting fluid and mucus from the upper small intestine. This method is particularly useful when stool sample tests are inconclusive or when Giardia infection is strongly suspected but difficult to confirm through other means.
How the String Test Works
The procedure involves a simple yet effective method to obtain a sample directly from the duodenum, where Giardia trophozoites often reside:
- Capsule Ingestion: A patient swallows a weighted gelatin capsule that has a string attached to it. The string's other end remains outside the mouth, typically taped to the cheek.
- Placement and Collection: The weighted capsule travels through the esophagus and stomach into the duodenum. The string acts as a guide and collector. Once in place, the capsule is left for approximately four hours, allowing the duodenal fluid and mucus, along with any present parasites, to adhere to the string.
- Retrieval: After the designated time, the string is carefully pulled out of the patient's stomach and mouth.
- Laboratory Examination: The collected fluid and mucus on the string are then smeared onto a microscope slide. A trained laboratory technician examines the sample under a microscope for the presence of Giardia trophozoites (the active, feeding stage of the parasite) or other parasitic elements.
Why the String Test for Giardia?
Giardia infection, or giardiasis, can cause symptoms like diarrhea, abdominal cramps, bloating, and weight loss. While stool tests are common for diagnosis, they might not always detect the parasite, especially if the shedding of cysts is intermittent. The string test provides a direct sample from the environment where Giardia thrives, increasing the likelihood of detection.
Advantages of the String Test:
- Direct Sampling: It collects duodenal contents, which can be richer in Giardia trophozoites than fecal samples.
- Increased Sensitivity: Can sometimes detect infections missed by conventional stool examinations.
- Patient Comfort: It is less invasive than an endoscopy and generally well-tolerated.
When is the String Test Recommended?
The string test is often considered when:
- A patient has symptoms suggestive of giardiasis, but multiple stool tests have returned negative results.
- There's a need to differentiate Giardia infection from other gastrointestinal conditions.
- Evaluating chronic or persistent parasitic infections that are difficult to diagnose.
For more information on giardiasis and its diagnosis, you can refer to resources from reputable health organizations like the Centers for Disease Control and Prevention (CDC).
