Gastrointestinal Health Marker Guide

Faecal occult blood

What this marker measures

Faecal occult blood is measured using a faecal immunochemical test (FIT); this detects hidden human blood in stool, which may indicate bleeding in the lower gastrointestinal tract. It is used as a non-invasive screening tool for colorectal cancer and may also be positive in other inflammatory or bleeding conditions, including IBD^1–4. FIT is specific for human haemoglobin and requires no dietary preparation.

‍This assay is issued under the European IVDR framework (the assay is classified IVDR Class C) with ARTG listing for use in Australian markets

Clinical associations*

Consider this marker when your patient presents with:

Lower GI symptoms

Altered bowel habits, rectal bleeding, unexplained change in stool colour, iron-deficiency anaemia, or other clinical features suggestive of lower-GI bleeding.

Colorectal cancer referral pathway

A positive result may prompt consideration of referral according to local colorectal referral pathways.

IBD context

May be positive in active intestinal inflammation and has been associated with increased likelihood of IBD diagnosis. In ulcerative colitis, a negative result may provide evidence of mucosal healing when interpreted alongside other clinical findings.

*In addition to the assay’s intended use, all clinical associations have been reviewed by the Microba science team to ensure clinical validity supported by Microba’s cited literature.

Interpreting the result

not detected

No human blood detected above the test threshold (10ug Hb/g faeces).

Lower-GI bleeding is less likely in this sample, but intermittent or low-level bleeding is not excluded. In ulcerative colitis, this may provide evidence of mucosal healing when interpreted alongside other clinical findings.

DETECTED

Human blood detected

Further medical assessment is warranted if the cause is unknown, symptoms persist, or red-flag symptoms are present.

^negative result does not exclude intermittent or low-level bleeding. If bleeding is clinically suspected, further investigation is recommended regardless of this result.

Patient management insights

Investigate the cause of detected faecal occult blood.

Clinical significance

Out-of-range lactoferrin requires referral to a medical practitioner if cause is unknown, persistent or red-flag symptoms are present.

Supplementation

Medical assessment is recommended when faecal occult blood is detected and the cause is unknown.

Tips for discussing out-of-range results

This test checks for tiny amounts of blood in your stool that you wouldn’t be able to see. Your result shows that blood has been detected, which can happen for several reasons, some straightforward, and some that need further investigation. The next step is referral to a medical practitioner to determine what’s going on

Evidence grading for patient management insights

The letter grades shown next to each patient management insight show the quality of the research behind it. Every insight provided has been through a rigorous review of the scientific literature and graded using the NHMRC Levels of Evidence, so you can see exactly how strong the evidence is before applying it in practice.

Faecal occult blood— Reference sourcesSource references for all clinical associations, interpretation definitions, and patient management insights on this card.

1. US Preventive Services Task Force. Screening for Colorectal Cancer: US Preventive Services Task Force Recommendation Statement. JAMA 325, 1965–1977 (2021).
2. Niedermaier, T., Balavarca, Y. & Brenner, H. Stage-Specific Sensitivity of Fecal Immunochemical Tests for Detecting Colorectal Cancer: Systematic Review and Meta-Analysis. Am J Gastroenterol 115, 56–69 (2020).
3. Hu, T., Zhang, Z., Song, F., Zhang, W. & Yang, J. Evaluation of Mucosal Healing in Ulcerative Colitis by Fecal Calprotectin vs. Fecal Immunochemical Test: A Systematic Review and Meta-analysis. Turk J Gastroenterol 34, 892–901 (2023).
4. Lee, E., Lee, G. H., Park, B., Ahn, S. S. & Noh, C.-K. Positive faecal immunochemical test predicts the onset of inflammatory bowel disease: A nationwide, propensity score-matched study. Front Immunol 14, 1128736 (2023).