A gastric culture is a test to examine a child's stomach contents for the bacteria that cause tuberculosis.
How the test is performed
A flexible tube is placed through the child's nose and into the stomach. The child may be given a glass of water and asked to swallow while the tube is inserted. Once the tube is in the stomach, the health care provider will remove a sample of the stomach contents using a syringe.
The tube is removed through the nose. The sample is sent to a laboratory, where it is placed in a special dish and watched for the growth of bacteria.
How to prepare for the test
Your child will need to fast (no food or drink, including water) for 8 to 10 hours before the test.
The sample is collected in the morning. Performing the test too soon after the tube is placed can affect the results. For this reason, your child will likely be admitted to the hospital for the night. The tube can then be placed in the evening, and the test done first thing in the morning.
How you prepare your child for this test depends on your child's age, past experiences, and level of trust. For information on how you can prepare your child, see the following topics:
- Infant test or procedure preparation (birth to 1 year)
- Toddler test or procedure preparation (1 to 3 years)
- Preschooler test or procedure preparation (3 to 6 years)
- School age test or procedure preparation (6 to 12 years)
- Adolescent test or procedure preparation (12 to 18 years)
How the test will feel
While the tube is being passed through the nose and throat, your child will feel some discomfort and may also feel the urge to vomit.
Why the test is performed
This gastric culture can help diagnose lung (pulmonary) tuberculosis in children. This method is used because children cannot cough up and spit out mucus until about age 8. They swallow the mucus, instead. (That is why young children only rarely spread tuberculosis to others.)
The test may also be done to help identify viruses, fungi, and bacteria in the gastric contents of patients with cancer, AIDS, or other conditions that cause a weakened immune system.
The bacteria that cause tuberculosis are not normally found in the stomach contents.
What abnormal results mean
If the bacteria that cause tuberculosis grow from the gastric culture, Mycobacterium tuberculosis is diagnosed. Because these bacteria are slow growing, it may take up to 6 weeks to confirm the diagnosis.
This test can also be used to detect other forms of bacteria that do not cause tuberculosis.
What the risks are
Anytime a nasogastric tube is inserted down the throat, there is a small chance it will enter the windpippe. If this happens, your child may cough, gasp, and have trouble breathing until the tube is removed. There is also a small chance that some of the stomach contents may enter the lung.
A test called a TB smear will be done first on the sample. If the results are positive, medical treatment may be started right away. A negative TB smear result does not rule out tuberculosis.
The final results of the gastric culture test may take several weeks. Your health care provider will decide whether to start treatment before knowing the test results.
Starke JR, Munoz FM. Tubercolosis (Mycobacterium Tuberculosis). In: Kliegman RM, Behrman RE, Jenson HB, Stanton BF, eds. Nelson Textbook of Pediatrics. 18th ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 212.