13C-bicarbonate breath test as a measure of gastric emptying

Radionuclide studies are widely used to estimate the gastric emptying rate of solids and liquids. Unfortunately, these methods carry the risk of radiation exposure and require expensive and complex equipment. Carbon-13, a stable, nonradioactive isotope, has been used successfully as a marker in the gastrointestinal tract for other purposes. A preliminary study using ingested NaH13CO3 and measuring 13CO2 breath excretion suggested that this test might be a simple, noninvasive, and inexpensive method for determining gastric emptying. To determine the efficacy of NaH13CO3 as a noninvasive marker for gastric emptying, the resulting 13CO2 breath excretion was determined simultaneously with standard radiolabeled meal measurements of gastric emptying of liquids and solids in 15 patients. 13CO2 breath excretion did not correlate with the gastric emptying of either solids or liquids, as determined by radionuclide techniques. These results suggest that NaH13CO3 is not a reliable indicator of gastric emptying. Factors other than gastric emptying may affect the rate of 13CO2 absorption and exhalation, rendering it unreliable as a measure of gastric emptying.