Understanding Lab Tests for Small Intestinal Bacterial Overgrowth (SIBO)
Written by Private MD Labs Medical Writing Team • Last Updated: September 8, 2025
Small Intestinal Bacterial Overgrowth (SIBO) is a condition where excessive bacteria grow in the small intestine, leading to digestive symptoms and nutrient malabsorption. While SIBO is typically diagnosed through specialized breath tests, blood testing plays a fundamental role in assessing the body's response to the condition and monitoring for nutritional complications.
Recommended Test
Methylmalonic Acid
This test measures methylmalonic acid levels in the blood, which can become elevated when vitamin B12 deficiency occurs due to SIBO-related malabsorption. Since B12 is required to convert methylmalonic acid to other compounds, a deficiency causes this acid to build up in the blood, making it a sensitive marker for detecting the nutritional impact of SIBO.
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Why Blood Testing is Important for SIBO
SIBO can interfere with the absorption of essential nutrients, particularly vitamin B12, which is absorbed in the small intestine. Blood tests are crucial for detecting these nutritional deficiencies and their metabolic consequences, helping healthcare providers understand the severity of malabsorption and guide appropriate treatment.
Understanding the Connection
The overgrowth of bacteria in SIBO can damage the intestinal lining and compete with the body for nutrients, particularly affecting vitamin B12 absorption. When B12 levels drop, methylmalonic acid accumulates because it cannot be properly metabolized, making this test valuable for assessing the metabolic consequences of SIBO even when other symptoms may be unclear.
Important Considerations
The information here is for educational purposes only and is not a substitute for professional medical advice. Always consult with a healthcare provider for diagnosis and treatment of SIBO and related nutritional complications.
