If low stomach acid is contributing to your SIBO, identifying it can change your treatment approach. But testing stomach acid levels is less straightforward than testing for SIBO itself. There is no simple at-home kit that provides a reliable result. The available options range from a gold-standard clinical test that is expensive and hard to find, to blood markers that provide indirect evidence, to popular online tests with no scientific validation. Understanding what each test actually measures, and what it does not, helps SIBO patients and their clinicians make informed decisions about whether and how to investigate gastric acid status.
The Heidelberg pH capsule test
The Heidelberg pH capsule test is considered the gold standard for measuring gastric acid production. The patient swallows a small pH-sensing capsule (approximately the size of a large vitamin pill) attached to a thin string for retrieval. The capsule transmits real-time pH readings to a receiver worn on the patient's belt. The test begins by measuring the baseline fasting gastric pH, then the patient drinks a solution of sodium bicarbonate (baking soda), which temporarily neutralizes stomach acid. The test measures how quickly and completely the stomach re-acidifies after the alkaline challenge, a process called acid rebound.
A healthy stomach with normal acid production will re-acidify to a pH below 3.0 within 20 minutes after a sodium bicarbonate challenge. Patients with hypochlorhydria show delayed or incomplete re-acidification. The test can also distinguish between different levels of acid impairment, from mild hypochlorhydria to complete achlorhydria. The main limitations are cost (typically $300-$500 out of pocket), limited availability (only certain gastroenterology and functional medicine clinics offer the test), and the need for an in-person visit.
Pepsinogen and gastrin blood markers
Blood tests measuring pepsinogen I, pepsinogen II, the pepsinogen I/II ratio, and fasting gastrin levels provide indirect evidence about gastric acid status. Pepsinogen I is produced by chief cells in the gastric corpus (the same region where parietal cells produce acid). Low pepsinogen I levels and a low pepsinogen I/II ratio indicate atrophy of the corpus mucosa and reduced acid-producing capacity. These markers were originally developed as screening tools for gastric cancer risk in Japan (the GastroPanel approach) but are useful for assessing gastric acid status in any clinical context.
Fasting gastrin is an indirect marker because gastrin is released in response to high gastric pH. When stomach acid is low, the antral G cells produce more gastrin in an attempt to stimulate acid production. Elevated fasting gastrin therefore suggests hypochlorhydria. However, gastrin can also be elevated by PPI use (which independently raises pH), gastrinoma (Zollinger-Ellison syndrome), and H. pylori infection. Clinical interpretation requires considering the full context.
- Pepsinogen I below 30 mcg/L suggests corpus atrophy and reduced acid production.
- Pepsinogen I/II ratio below 3.0 is a strong indicator of corpus atrophy.
- Fasting gastrin above 100 pg/mL (in the absence of PPI use) suggests hypochlorhydria.
- These tests can be ordered through standard laboratory panels. They are covered by most insurance plans when ordered with appropriate diagnostic codes.
- The GastroPanel (a combined panel of pepsinogen I, pepsinogen II, gastrin-17, and H. pylori antibodies) is available in some markets as a comprehensive gastric health screen.
The baking soda test: why it is unreliable
The at-home baking soda test is widely promoted on health websites and social media. The protocol involves drinking a solution of 1/4 teaspoon of baking soda (sodium bicarbonate) in 4-8 ounces of water on an empty stomach and timing how long it takes to produce a belch. The theory is that adequate stomach acid will react with the bicarbonate to produce carbon dioxide gas, causing a belch within 3 to 5 minutes, while low stomach acid will produce a delayed or absent belch.
There are no published studies validating this test against any reference standard for gastric acid measurement. The timing and intensity of belching depend on many factors unrelated to stomach acid levels, including the rate of gastric emptying, the volume of air swallowed during drinking, individual variation in gas sensitivity, and the volume and concentration of the bicarbonate solution. The test produces frequent false positives and false negatives and should not be used as a basis for clinical decisions.
âšī¸The baking soda test is popular because it is free and easy. But it has no validated diagnostic accuracy. If you suspect low stomach acid, pursue validated testing through your healthcare provider rather than relying on this unproven method.
The betaine HCl challenge protocol
The betaine HCl challenge is a protocol used by some functional medicine and integrative practitioners to assess stomach acid levels indirectly. The protocol involves taking a capsule of betaine HCl (typically 500-650 mg) with a protein-containing meal and monitoring for symptoms. In a person with normal or high stomach acid, the additional acid produces a warm or burning sensation in the stomach. In a person with low stomach acid, the supplemental acid is tolerated without discomfort, and subsequent meals may involve gradually increasing the number of capsules until warmth is felt, with the preceding dose considered the therapeutic level.
This protocol is not validated in peer-reviewed literature. The subjective nature of the warmth/burning sensation, individual variation in visceral sensitivity, and potential for placebo effects limit its reliability. Additionally, betaine HCl is contraindicated in patients with active peptic ulcers, erosive gastritis or esophagitis, or current NSAID use, as supplemental acid can worsen these conditions. The betaine HCl challenge should only be performed under the guidance of a knowledgeable practitioner, not self-directed based on internet protocols.
When to seek medical evaluation
For SIBO patients, investigating stomach acid levels makes the most sense in specific clinical scenarios. If you have SIBO along with iron deficiency or B12 deficiency that does not respond well to supplementation, low stomach acid should be investigated. If you have been on a PPI for more than one year without reassessment, both the PPI indication and your gastric acid status warrant review. If you have autoimmune conditions (particularly autoimmune thyroid disease or type 1 diabetes), screening for autoimmune gastritis with pepsinogen and gastrin levels is warranted. If you are over 60 with recurrent SIBO and no other identified root cause, age-related hypochlorhydria becomes a relevant consideration.
In practice, most clinicians will start with the pepsinogen and gastrin blood panel, which is inexpensive and widely available. If results suggest hypochlorhydria, the Heidelberg test can provide definitive confirmation. If the Heidelberg test is not accessible, clinical management decisions can often be made based on the blood markers combined with clinical history and risk factors.
â ī¸This article is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider with questions about a medical condition.