A gastric culture is a test done on children that looks at the stomach (gastric) contents to identify the microorganism that causes tuberculosis (mycobacterium tuberculosis).

A gastric culture is done in children because when they cough up tuberculosis bacteria from the lung, rather than spitting it out, they swallow the mucus. Children cannot cough up mucus and then spit it out until about age 8. That is also why young children cannot spread tuberculosis.

A naso-gastric tube is placed through the nose into your child's stomach. Your child may be given a glass of water and asked to swallow while the tube is advanced. Once the tube is in the stomach, a syringe is used to withdraw a sample. The tube is then removed through the nose, and the sample is taken to the laboratory.

Your child will need to fast for 8 to 10 hours before the test. The sample is collected in the morning. Conducting 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 performed 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 may feel some discomfort and may also feel the urge to vomit.

This test is useful in the diagnosis of pulmonary (lung) tuberculosis in children in whom an adequate sputum sample cannot be obtained.

The microorganism that causes tuberculosis is not normally present in gastric culture.

The diagnosis of tuberculosis is made if Mycobacterium tuberculosis, the microorganism that causes tuberculosis, is grown from the gastric culture. Because this bacteria is slow to grow, it may take up to 6 weeks for the diagnosis to be confirmed. There are other mycobacteria that do not cause tuberculosis which may also be detected by this test.

Anytime a naso-gastric tube is inserted down the back of the throat, there is a small chance that the tube will enter the trachea instead of the esophagus. If this happens, your child may cough, gasp, and have trouble breathing. This is reversed by taking the tube out. There is also a small chance that some of the stomach contents may enter the lung.

A preliminary test, called an "AFB smear," will be performed immediately on the sample, and if the results are positive, treatment is usually started right away. A negative AFB smear result, however, does not rule out tuberculosis.

The final results of the gastric culture test may not be known for 6 weeks, as it may take that long for the tuberculosis microoganism to grow. Your physician will decide whether to start treatment before the test results are known.