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A gastric culture is a test to examine a child's stomach contents for the bacteria that causes tuberculosis.

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.

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.

The preparation you can provide for this test depends on your child's age, previous experiences, and level of trust. For specific information regarding 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)

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.

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 bacteria that causes tuberculosis is not normally found in stomach contents.

Note: Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.

If the bacteria that causes tuberculosis grows from the gastric culture, the diagnosis of Mycobacterium tuberculosis is made. 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.

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 preliminary test, called a TB smear, will be done first on the sample. If results are positive, medical treatment may be started right away. A negative TB smear result, however, 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 the test results are known.

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.

Updated by: David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine; Jatin M. Vyas, MD, PhD, Assistant Professor in Medicine, Harvard Medical School, Assistant in Medicine, Division of Infectious Disease, Department of Medicine, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.