How is SIBO diagnosed?

    Written by:
    Gabrielle Fundaro

    Fact-checked

    by:

    Kamal Patel, Nick Milazzo
    Last Updated: May 16, 2025

    Small intestinal bacterial overgrowth (SIBO) is diagnosed using breath tests or duodenal aspirate cultures, though a lack of standardization complicates accurate diagnosis. A concentration of 10^3 to 10^5 CFU/mL in a fluid sample is generally accepted as indicative of SIBO.

    SIBO often occurs with other GI diseases that have overlapping symptoms, which can complicate diagnosing either accurately.[1]

    SIBO can be diagnosed with breath tests or a duodenal aspirate culture (a lab test done on a small fluid sample from the small intestine), but the lack of standardization makes accurate diagnosis challenging. Breath tests are an indirect way to measure bacteria in the small intestine, but their ease and low invasiveness make them a more common diagnostic tool than the fluid test.[2][3]

    Clinicians have yet to reach a consensus on diagnostic criteria for a positive result of either test, but it’s generally accepted that SIBO is present when there is a concentration of 103 to 105 colony forming units per milliliter (CFU/mL) in a fluid sample. [2][3]