Gut Health and Blood Tests: The Biomarkers That Connect Them

The gut has earned its reputation as the body’s "second brain," and for good reason. Housing trillions of microorganisms and approximately 70% of the immune system, the gastrointestinal tract influences everything from nutrient absorption and immune function to mental health and metabolic regulation. What many people don’t realise is that the state of your gut health leaves detectable traces in standard blood tests — if you know where to look.

While stool tests and microbiome analyses provide direct information about gut flora, blood biomarkers offer a complementary and often more accessible picture of how gut health is affecting your overall wellbeing. At Yearly, we help you connect these dots by analysing your blood work for patterns that may indicate underlying gut dysfunction.

Inflammatory Markers: hs-CRP and ESR

Chronic low-grade inflammation is one of the hallmark consequences of poor gut health. When the intestinal barrier is compromised — a condition colloquially known as "leaky gut" or, more accurately, increased intestinal permeability — bacterial components such as lipopolysaccharides (LPS) can enter the bloodstream and trigger systemic inflammation.

High-sensitivity C-reactive protein (hs-CRP) is the most accessible blood marker for this type of inflammation. While hs-CRP can be elevated for many reasons, persistently raised levels in the absence of acute infection or injury should prompt consideration of gut-driven inflammation. The erythrocyte sedimentation rate (ESR) provides additional inflammatory context. A study in Gut demonstrated that increased intestinal permeability is associated with elevated systemic inflammatory markers and precedes the development of several chronic diseases (Bischoff et al., 2014).

Iron Studies and Nutrient Deficiencies

The gut is where nutrient absorption occurs, and any compromise to the intestinal lining directly impacts how effectively you absorb essential vitamins and minerals. Iron deficiency is one of the most common indicators of poor gut health, particularly when dietary intake appears adequate.

Conditions such as coeliac disease, inflammatory bowel disease (IBD), and even small intestinal bacterial overgrowth (SIBO) can impair iron absorption, leading to low ferritin levels despite a nutritious diet. A full iron studies panel — including serum iron, ferritin, transferrin, and transferrin saturation — can reveal malabsorption patterns that point toward gut dysfunction.

Beyond iron, vitamin B12 and folate deficiencies are also strongly linked to gut health. Vitamin B12 is absorbed in the terminal ileum, and conditions affecting this region (such as Crohn’s disease) can cause deficiency even with adequate dietary intake. Folate absorption occurs primarily in the jejunum and can be impaired by coeliac disease and certain medications. Low levels of either nutrient should prompt investigation into gut function (Green et al., 2017).

Vitamin D

Vitamin D deficiency has been consistently associated with gut disorders, and the relationship appears to be bidirectional. Poor gut health impairs vitamin D absorption (it is a fat-soluble vitamin requiring adequate bile and fat digestion), while vitamin D deficiency itself compromises gut barrier integrity and immune regulation within the gut.

A study in Therapeutic Advances in Gastroenterology found that vitamin D supplementation improved intestinal barrier function and reduced markers of intestinal inflammation in patients with IBD (Fletcher et al., 2019). If your blood work consistently shows low vitamin D despite adequate sun exposure and supplementation, impaired gut absorption should be considered as a potential cause.

Full Blood Count (FBC) Patterns

A standard full blood count can reveal subtle clues about gut health. Microcytic anaemia (small red blood cells with low haemoglobin) typically indicates iron deficiency, while macrocytic anaemia (large red blood cells) suggests B12 or folate deficiency — both of which can stem from malabsorption.

Elevated white blood cell counts, particularly eosinophils, may indicate allergic or parasitic gut conditions. Low lymphocyte counts can suggest immune dysregulation, which is often rooted in gut immune function. Even platelet counts can be relevant, as thrombocytosis (elevated platelets) is sometimes seen in active inflammatory bowel disease.

Liver Function Tests

The liver and gut are intimately connected through the portal venous system — blood from the intestines flows directly to the liver for processing. When gut permeability is increased, the liver bears the burden of filtering bacterial toxins and inflammatory mediators that have entered the bloodstream.

Mildly elevated liver enzymes, particularly GGT and ALT, can be an indirect signal of gut-derived inflammation. Non-alcoholic fatty liver disease (NAFLD), which is increasingly prevalent in Australia, has strong associations with gut dysbiosis and increased intestinal permeability. Research published in Nature Reviews Gastroenterology & Hepatology has established that the gut-liver axis plays a central role in the pathogenesis of NAFLD (Leung et al., 2016).

Blood Sugar and Metabolic Markers

Emerging research has revealed fascinating connections between gut microbiome composition and metabolic health. Certain gut bacterial populations are associated with improved insulin sensitivity, while dysbiosis (imbalanced gut flora) is linked to insulin resistance and impaired glucose metabolism.

Elevated fasting insulin, rising HbA1c, or an unfavourable lipid profile may all have gut health components. While these markers don’t directly measure gut function, they can indicate metabolic consequences of gut dysfunction that warrant further investigation. Addressing gut health through dietary changes, probiotics, and reducing processed food intake has been shown to improve metabolic markers in clinical trials.

Coeliac Screening: tTG-IgA

Coeliac disease affects approximately 1 in 70 Australians, yet up to 80% of cases remain undiagnosed. The tissue transglutaminase IgA (tTG-IgA) antibody test is a simple blood test that can screen for this autoimmune condition. Coeliac disease causes significant damage to the small intestinal lining and is a major cause of nutrient malabsorption, iron deficiency, and chronic fatigue.

If your blood work shows unexplained nutrient deficiencies, particularly iron and B12, alongside fatigue and digestive symptoms, coeliac screening should be requested. Total IgA levels should be checked simultaneously, as IgA deficiency (present in 2–3% of coeliac patients) can cause false-negative results.

Connecting the Dots with Yearly

Gut health rarely presents as a single abnormal blood test. Instead, it creates a pattern — low iron, low vitamin D, mildly elevated inflammation, borderline liver enzymes, and emerging metabolic dysfunction. Recognising this pattern requires looking at your blood work holistically, which is precisely what Yearly’s AI-powered analysis is designed to do.

Upload your blood test results and let our platform identify the connections between your biomarkers. Because understanding your gut health starts with understanding your blood work.

References

1. Bischoff, S.C., et al. (2014). "Intestinal Permeability — A New Target for Disease Prevention and Therapy." BMC Gastroenterology, 14, 189.
2. Green, R., et al. (2017). "Vitamin B12 Deficiency." Nature Reviews Disease Primers, 3, 17040.
3. Fletcher, J., et al. (2019). "Vitamin D and Inflammatory Bowel Disease." Therapeutic Advances in Gastroenterology, 12, 1756284819864379.
4. Leung, C., et al. (2016). "The Role of the Gut Microbiota in NAFLD." Nature Reviews Gastroenterology & Hepatology, 13(7), 412–425.