Could Your Blood Tests Already Be Showing Signs of Autoimmune Disease?

Almost every week, a new client sends me a folder full of their current and previous blood test results.

Some have recently been diagnosed with Hashimoto’s thyroiditis. Others have rheumatoid arthritis, psoriasis, coeliac disease, chronic fatigue syndrome or alopecia areata. Many don’t yet have a diagnosis at all—they simply know something isn’t right. They’re exhausted, they’re losing their hair, they’re struggling with joint pain or digestive symptoms, and despite having multiple blood tests over the years they’ve repeatedly been told that everything looks “normal”.

It’s one of the most frustrating conversations I have with clients because, more often than not, those blood tests aren’t telling us nothing. They’re simply not being interpreted in the context of how the immune system actually works.

One of the first things I do when I review a client’s history is go back through every full blood count they’ve had. Not because I expect one result to reveal the answer, but because the immune system often leaves clues long before a diagnosis is made. Sometimes those clues are subtle. Sometimes they’re patterns that have persisted for years. Occasionally they’re hiding in plain sight.

This is one of the reasons I find autoimmune disease so fascinating. The immune system is incredibly intelligent, but it’s also incredibly complex. It doesn’t simply switch on or off, nor is it either “strong” or “weak”. Instead, it’s a highly coordinated network of specialised immune cells that are constantly communicating with one another, responding to infections, repairing damaged tissue, maintaining tolerance and deciding what belongs inside your body and what doesn’t.

When autoimmune disease develops, that conversation changes.

For reasons that vary from person to person, the immune system begins to lose tolerance to the body’s own tissues. In someone with Hashimoto’s thyroiditis, that may be the thyroid gland. In alopecia areata, it’s the hair follicle. In rheumatoid arthritis, it’s the joints. In coeliac disease, gluten triggers an immune response that damages the lining of the small intestine.

The diagnosis may differ, but the common thread is immune dysregulation.

Understanding why that dysregulation has developed—and which parts of the immune system are involved—is where functional medicine becomes particularly interesting.

Why a Full Blood Count Can Tell Us More Than You Think

The full blood count (FBC) is one of the most frequently requested blood tests in medicine. Almost everyone with an autoimmune condition will have had one, often many times over. Yet in my experience, it’s also one of the most underappreciated investigations.

Most clinicians understandably use it to rule out problems such as anaemia, infection or blood disorders. Those are incredibly important uses of the test. However, I also look at it through a different lens.

Rather than asking whether each number falls inside the laboratory reference range, I’m interested in the relationships between those numbers. I want to understand what they might be telling me about the behaviour of the immune system over time.

Take neutrophils, for example. These are your body’s rapid-response immune cells and form part of what we call the innate immune system. They’re often the first cells to arrive when there’s an infection, injury or inflammatory trigger. While they’re classically associated with bacterial infections, they can also increase in response to chronic inflammation, smoking, poor sleep, psychological stress, surgery and even intense exercise. Seeing persistently higher neutrophils doesn’t automatically indicate disease, but it may suggest that the innate immune system has remained activated for longer than we would normally expect.

Lymphocytes tell a different story altogether. This group includes some of the most sophisticated immune cells in the body, including T cells, B cells and natural killer (NK) cells. These cells coordinate immune memory, produce antibodies, destroy virus-infected cells and regulate immune tolerance. Changes in lymphocyte numbers can occur following viral infections, chronic stress, immune exhaustion, certain medications or ongoing immune activation. Again, there isn’t a single interpretation, but when viewed alongside symptoms and the rest of the blood count they can provide valuable insight into how the adaptive immune system may be behaving.

Monocytes are another cell population I pay close attention to. Often described as the body’s clean-up crew, they remove damaged tissue, mature into macrophages and help coordinate both inflammation and healing. When they’re consistently elevated, I begin asking whether there’s an unresolved inflammatory process, chronic infection or ongoing tissue damage keeping the immune system engaged.

Eosinophils often open an entirely different line of enquiry. Although they’re best known for their role in allergies and parasitic infections, they can also provide clues about allergic inflammation, asthma, eczema, histamine intolerance and, in some individuals, mast cell activation. Given how frequently these overlap with autoimmune disease, they’re never a number I ignore.

The important point is this: I rarely interpret any of these cells in isolation. It’s the patterns between them—and how those patterns change over months or even years—that often provide the greatest insight.

In fact, some of the most interesting developments in immune research are no longer looking at individual cell counts at all. Instead, researchers are examining how these cells interact with one another to create a broader picture of immune health. One of the simplest examples of this is something called the Systemic Immune-Inflammation Index (SII), a marker that’s beginning to attract increasing attention in autoimmune disease and chronic inflammatory conditions.

The Systemic Immune-Inflammation Index

One of the challenges with interpreting a full blood count is that we often look at each result in isolation. We ask whether the neutrophils are within range, whether the lymphocytes are normal and whether the platelets are too high or too low. While those questions are important, our immune system doesn’t work in isolation, so why should we interpret it that way?

This is where the SII becomes particularly interesting.

Rather than focusing on a single immune cell, the SII combines three values that are already measured as part of a routine full blood count: neutrophils, lymphocytes and platelets. Together, they provide an indication of the balance between inflammatory activity and immune regulation.

Over the past few years, researchers have begun investigating the SII across a wide range of chronic diseases, including autoimmune conditions, cardiovascular disease, cancer and metabolic disorders. Although it isn’t yet used routinely in clinical practice, the evidence is growing that it may provide a more sensitive reflection of low-grade systemic inflammation than looking at any one cell count alone.

This is particularly relevant in autoimmune disease because one of the biggest misconceptions is that inflammation always shows up as a raised CRP or ESR.

In reality, that’s often not the case.

Some of the people I see with the most significant autoimmune symptoms have completely normal inflammatory markers. They may have debilitating fatigue, joint pain, brain fog, hair loss or digestive symptoms, yet their CRP is reassuringly low. That doesn’t necessarily mean the immune system is calm. It simply tells us that we’re looking at one small part of a much bigger picture.

The SII is one example of how researchers are beginning to move away from asking, “Is there inflammation?” and towards asking, “How is the immune system behaving?”

I suspect we’ll see much more of this over the next decade.

Why I Sometimes Recommend Advanced Immune Testing

As fascinating as the full blood count can be, it still has its limitations.

Imagine trying to understand how a football team is performing by standing outside the stadium and simply counting how many players walked in. You’d know the team was there, but you wouldn’t know who was defending, who was attacking, who was injured or whether they were working together effectively.

The same is true of the immune system.

A routine blood count tells us how many lymphocytes are present, but it doesn’t tell us which types of lymphocytes they are. That’s important because lymphocytes aren’t one cell. They’re an entire family of specialised immune cells, each carrying out a very different role.

This is where advanced immune phenotyping can become incredibly valuable, particularly for people with complex autoimmune disease, recurrent infections, unexplained immune dysfunction or those who simply aren’t responding as expected to treatment.

Rather than looking at one overall lymphocyte count, these tests allow us to examine the different immune cell populations in far greater detail. We can look at helper T cells (CD4 cells), cytotoxic T cells (CD8 cells), natural killer cells, regulatory T cells, B cells and, in some cases, even different stages of B-cell development and activation.

Why does that matter?

Because autoimmune disease isn’t one disease.

Even two people with exactly the same diagnosis can have very different immune signatures.

One person with Hashimoto’s thyroiditis may have evidence of ongoing viral immune activation, while another appears to have significant immune dysregulation driven by impaired regulatory T-cell function. Someone with alopecia areata may demonstrate a different pattern again. If we only look at the diagnosis, those individuals appear identical. If we look at the immune system itself, they can look remarkably different.

That’s where personalised medicine becomes so exciting.

T Cells, B Cells and Why They Matter

When people hear the term “immune system”, they often imagine one defence mechanism working against infection. In reality, the immune system is made up of highly specialised teams that constantly communicate with one another.

T cells act more like the commanders. They coordinate immune responses, destroy infected cells and help determine whether an immune reaction should continue or stop. Within that family are regulatory T cells, often called Tregs, whose job is to prevent the immune system from attacking healthy tissue. It’s hardly surprising that these cells have become one of the most studied areas in autoimmune research.

B cells have a different role. Their primary job is producing antibodies. Those antibodies are incredibly useful when fighting infections, but in autoimmune disease they can sometimes become misdirected, producing antibodies against the body’s own tissues instead. Thyroid antibodies in Hashimoto’s disease are one example. Rheumatoid factor and anti-CCP antibodies in rheumatoid arthritis are another.

This is why understanding whether T-cell regulation, B-cell activation or both appear to be driving the immune response can provide valuable insight when we’re trying to understand an individual’s disease.

It’s also one of the reasons I don’t believe autoimmune disease is ever simply about “boosting” or “suppressing” the immune system.

What we’re really trying to achieve is something much more sophisticated.

We’re trying to restore balance.

Bringing Everything Together

One of the biggest lessons I’ve learnt throughout my own health journey and from working with hundreds of people living with autoimmune disease is that every result tells part of the story, but no single test tells the whole story.

A full blood count may reveal subtle immune patterns. The Systemic Immune-Inflammation Index may provide another layer of understanding. Advanced immune phenotyping can tell us even more about which immune cells are involved. Alongside this, I may also consider thyroid antibodies, nutritional status, gut health, infections, environmental triggers, genetics and a person’s clinical history.

Individually, each investigation has limitations.

Together, they begin to tell a coherent story.

Ultimately, that’s what functional medicine is about. It’s not collecting more tests for the sake of it. It’s about understanding why the immune system has become dysregulated in the first place and using that information to create a personalised plan that supports immune tolerance rather than simply masking symptoms.

I genuinely believe we’re entering a new era of autoimmune medicine. Rather than treating everyone with the same diagnosis in exactly the same way, we’re beginning to recognise that each person’s immune system is unique. The more we understand those differences, the better equipped we’ll be to help people regain their health.

And perhaps that’s the most exciting part of all. Your blood tests aren’t simply a collection of numbers. They’re a conversation with your immune system. The more we learn to interpret that conversation, the more opportunities we have to understand what’s really driving disease—and, more importantly, what we can do about it.

Ready to Understand What’s Really Driving Your Autoimmune Disease?

If you’ve been told your blood tests are “normal” but you still don’t feel like yourself, it’s worth remembering that symptoms always have a reason.

My approach is about looking beyond a diagnosis to understand the underlying factors influencing your immune system, from gut health and chronic infections to nutrient status, stress, hormones and immune regulation.

If you’re ready to start making meaningful changes to your health, I’ve created a free step-by-step guide to help you begin.

Download your free copy of The Autoimmune Recovery Plan for simple, practical steps you can take now to support your body, reduce overwhelm and start moving in the right direction.

👉 Download your free guide here

Frequently Asked Questions

Can a full blood count detect autoimmune disease?

Not on its own. A full blood count cannot diagnose an autoimmune disease, but it can provide valuable clues about how your immune system is functioning. Looking at patterns in immune cells alongside your symptoms, medical history and other laboratory testing often provides much more insight than any single result.

What blood tests are important for autoimmune disease?

That depends on your symptoms and diagnosis, but I often review a combination of a full blood count, inflammatory markers such as CRP and ESR, autoimmune antibodies, thyroid function, vitamin and mineral status, iron studies, vitamin D, zinc and, where appropriate, advanced immune phenotyping and functional testing.

What are T cells and B cells?

T cells and B cells are both types of white blood cell that form part of your adaptive immune system. T cells help coordinate and regulate immune responses, while B cells produce antibodies. In autoimmune disease, both can become dysregulated, contributing to the immune system attacking healthy tissues.

Why can my blood tests be normal if I still feel unwell?

This is one of the most common frustrations I see in clinic. Standard blood tests are designed to detect disease, but they don’t always explain why you’re experiencing symptoms. They also don’t capture every aspect of immune function. This is why looking at patterns, trends and, in some cases, more advanced testing can be so valuable.

Should everyone have advanced immune testing?

Not necessarily. Many people can make significant progress with a detailed clinical history, routine blood work and targeted functional testing. I tend to reserve advanced immune phenotyping for more complex cases, unexplained autoimmune symptoms or when someone isn’t responding as expected.

What is immune phenotyping?

Immune phenotyping is an advanced blood test that measures different populations of immune cells, such as T cells, B cells and natural killer (NK) cells. Rather than simply counting white blood cells, it provides a much more detailed picture of how the immune system is functioning.