I started writing this article because I lived it.
About eighteen months ago, I hit a wall. Not the kind where you have a bad week and bounce back. The kind where you wake up after eight hours and your first thought is I could sleep for another four. Where you're three coffees deep by 11am and still can't focus on a spreadsheet. Where your partner asks if you're okay and you say "yeah, just tired" for the sixth week in a row.
I work at Bloody Good. I literally have access to every blood test we sell. And it still took me embarrassingly long to actually order one. Because fatigue is so ordinary that you stop questioning it. Everyone's tired. You're busy. You're stressed. It's just... life now. Right?
Maybe. But also, maybe not.
When I finally tested, my ferritin was sitting at 28. Technically within the reference range. But at the low end. Low enough that my GP said it was almost certainly contributing to how I was feeling. Three months of supplementation later, I noticed a real difference. Not cured of everything. But noticeably, measurably better. (My experience isn't universal. Supplementation outcomes depend on individual circumstances and should be guided by a clinician.)
That experience changed how I think about fatigue. Not every tired person has low iron. But every persistently tired person deserves to know whether something in their blood work is contributing to how they're feeling.
This article is the guide I wish I'd had back then. It walks through the key blood tests clinicians typically consider when someone presents with fatigue, what each one measures, and why it matters. No scare tactics, no promises. Just the practical information that might help you figure out what to check first.
A note before we get into it
The information in this article is general. It's not a substitute for a conversation with your GP or clinician.
Blood tests are one piece of a larger picture. Results need to be interpreted alongside your symptoms, medical history, medications, and lifestyle. A single result outside the reference range doesn't automatically mean something is wrong. Results within range don't guarantee you'll feel great. I know that firsthand.
If you have known medical conditions, are pregnant, or are on prescription medications, use this as a starting point for a conversation — not a diagnosis.
Why "I'm just tired" deserves a closer look
I used to get stuck at this point. I'd think about getting tested, then talk myself out of it. It's probably just sleep. Or stress. Or the fact that I haven't exercised properly in three months.
All of those things matter. Lifestyle factors are the most common contributors to fatigue in otherwise healthy people. Poor sleep quality, not enough movement, chronic stress, dehydration, too many beers on the weekend. The usual.
But "usual" doesn't mean "only."
Fatigue is also one of the earliest symptoms of conditions that are straightforward to identify with basic blood work — if someone thinks to check. Iron deficiency is one of the most common nutritional deficiencies in Australia, and it can drag your energy down well before it progresses to full anaemia. Thyroid issues develop so gradually that people mistake them for ageing. Vitamin D deficiency, in one of the sunniest countries on the planet, affects roughly one in four Australian adults according to the Australian Bureau of Statistics (2011–12 Australian Health Survey). In Victoria and the ACT during winter, that number climbs to nearly half.
The point isn't to catastrophise. It's to stop assuming that "tired is just how I am now" when a handful of tests might help identify a factor worth discussing with your GP.
I mean, my fix was iron tablets. Not exactly cutting-edge medicine. But nobody had thought to check.
The blood tests that actually matter for fatigue
When clinicians investigate persistent fatigue, they're not looking for a single magic number. They're looking for patterns. Several markers together that either rule things in or rule things out.
These are the tests that come up most often. I've included a "What your clinician is thinking" framing because I find it useful. It helps explain why these tests get ordered and what the results mean in practice.
1. Full Blood Count (FBC)
What it measures
A Full Blood Count is the broadest starting point. It looks at your red blood cells, white blood cells, haemoglobin, haematocrit, and platelets.
Why it matters for fatigue
Haemoglobin is the protein that carries oxygen around your body. When it's low (anaemia, basically), everything has to work harder. You feel it as persistent tiredness, shortness of breath when you exert yourself, difficulty concentrating. Sometimes lightheadedness.
White blood cell count adds context too. Persistently elevated or depressed white cells might point toward inflammation, infection, or immune system activity that could be contributing to how you feel.
What your clinician is thinking
"Is oxygen-carrying capacity adequate? Are there signs of anaemia, infection, or something immune-related that warrants a closer look?"
An FBC doesn't give you the answer. It tells you where to look next. That's why it's usually the first test ordered.
Test it with Bloody Good:
Biomarker info: Haemoglobin · White Blood Cell Count
Product: Full Blood Count (FBC) Blood Test
2. Iron Studies (including Ferritin)
What it measures
Iron studies include serum iron, ferritin (stored iron), transferrin saturation, and total iron-binding capacity (TIBC). Ferritin is the one most clinicians pay closest attention to for fatigue.
Why it matters for fatigue
This is the one that got me. Iron is essential for haemoglobin production and cellular energy. When stores are depleted, fatigue is often the first thing you notice — sometimes well before haemoglobin drops far enough to flag on an FBC.
The frustrating part: you can have a completely "normal" FBC and still have low ferritin. If your GP only orders a Full Blood Count and it comes back fine, they might not dig further. You go home thinking you're fine when your iron stores are running on fumes.
This is especially common in menstruating women, endurance athletes, vegetarians and vegans, frequent blood donors, and people with gut conditions that affect absorption. If any of those describe you and you're tired all the time, ferritin is worth checking. Probably first.
One caveat: ferritin can also be elevated by inflammation, liver conditions, or other factors. A single reading is always interpreted in context, not on its own. Some clinicians also use a higher functional threshold than the standard lab reference range when investigating fatigue, though thresholds vary between practitioners.
What your clinician is thinking
"Are iron stores adequate to support energy production, or is there early depletion flying under the radar?"
Test it with Bloody Good:
Biomarker info: Ferritin
3. Thyroid Function Test (TSH, Free T3, Free T4)
What it measures
TSH (thyroid-stimulating hormone), Free T4 (thyroxine), and Free T3 (triiodothyronine). These are the hormones that regulate your metabolic rate.
Why it matters for fatigue
Your thyroid works like a thermostat for your metabolism, setting the pace for how quickly your body burns energy. TSH is the signal telling the thermostat to adjust. T3 and T4 are the actual output.
When the thyroid underperforms (hypothyroidism), everything slows down. Fatigue, weight gain, sensitivity to cold, dry skin, brain fog. It affects women more often than men and tends to develop gradually over years, which makes it easy to dismiss as "just getting older."
That's one of the trickiest things about thyroid issues. The symptoms are so generic (tired, cold, gaining weight, can't think straight) that they overlap with about fifteen other things. Which is exactly why testing matters. You can't distinguish between "I need more sleep" and "my thyroid isn't pulling its weight" based on symptoms alone.
An elevated TSH with low Free T4 is a classic hypothyroid pattern. But subclinical thyroid dysfunction — where TSH is mildly elevated but T4 is still within range — can also contribute to fatigue. Your GP can advise whether that's worth investigating further.
What your clinician is thinking
"Is thyroid function contributing to this person's fatigue, weight changes, or mood symptoms? Or can we rule it out?"
4. Vitamin D
What it measures
Serum 25-hydroxyvitamin D, the storage form that reflects your overall vitamin D status.
Why it matters for fatigue
Vitamin D plays a role in muscle function, immune regulation, mood, and energy metabolism. Deficiency has been associated with fatigue, muscle weakness, low mood, and reduced exercise tolerance.
Australia has a massive vitamin D deficiency problem, and the numbers catch most people off guard. One in four adults are deficient according to the ABS (2011–12 Australian Health Survey), and that's a national average. In Victoria, ACT, and Tasmania during winter, nearly half the population drops below adequate levels. Even in summer, 14% of Australians are deficient. In a country where we're told to slip-slop-slap from September onwards.
People at higher risk include anyone who spends most of their time indoors (which, let's be honest, describes a lot of office workers), people with darker skin, those who cover their skin for cultural or medical reasons, shift workers, and anyone living south of Sydney.
I assumed vitamin D deficiency was a northern-hemisphere problem. It's not.
What your clinician is thinking
"Could low vitamin D be contributing to fatigue, muscle complaints, or mood changes? Is the level low enough to warrant supplementation?"
5. Vitamin B12 and Folate
What it measures
Blood levels of vitamin B12 (cobalamin) and folate (vitamin B9). Both are essential for red blood cell production, neurological function, and DNA synthesis.
Why it matters for fatigue
B12 deficiency can cause fatigue, weakness, cognitive difficulties, and a type of anaemia where red blood cells become abnormally large and dysfunctional (macrocytic anaemia). It can also cause neurological symptoms like tingling, numbness, and balance issues that are easy to brush off until they're not.
Higher-risk groups include vegans and strict vegetarians (B12 comes primarily from animal products), older adults (absorption decreases with age), people taking metformin or proton pump inhibitors, and anyone with digestive conditions affecting the stomach or small intestine.
Folate deficiency presents similarly. Testing both together gives a clearer picture of whether a nutritional gap might be part of the fatigue equation.
What your clinician is thinking
"Could B12 or folate deficiency explain the fatigue, or the blood cell changes we're seeing on the FBC?"
Test it with Bloody Good:
Product: Vitamin B12 Blood Test · Folate Blood Test
6. HbA1c (Glycated Haemoglobin)
What it measures
Your average blood sugar levels over the preceding 2–3 months.
Why it matters for fatigue
Blood sugar dysregulation is an underappreciated contributor to tiredness. When glucose control is impaired — whether that's pre-diabetes, insulin resistance, or established type 2 diabetes — energy becomes unpredictable. The afternoon crash, the persistent low-grade flatness, the brain fog that lifts after you eat and comes right back an hour later. That pattern.
HbA1c is useful because it looks at the trend, not a single moment. Your fasting glucose might look fine on the morning of your blood test while your average blood sugar exposure over weeks has been gradually drifting upward. HbA1c catches that drift.
Given that pre-diabetes typically develops without obvious symptoms for years, this can be one of the most revealing tests for persistent, unexplained fatigue. Especially if you also have abdominal weight gain, a family history of diabetes, or elevated triglycerides.
What your clinician is thinking
"Is blood sugar regulation stable, or is there a metabolic pattern that could be contributing to how this person feels?"
7. CRP (C-Reactive Protein)
What it measures
CRP is a protein your liver produces in response to inflammation. A high-sensitivity version (hs-CRP) picks up low-grade inflammation that might not cause obvious symptoms.
Why it matters for fatigue
CRP and other inflammation markers work like smoke detectors. They signal that something is causing irritation somewhere in your body without pinpointing the exact location.
Chronic low-grade inflammation has been linked to fatigue, brain fog, and reduced energy across conditions ranging from autoimmune disease to metabolic syndrome to lingering infection. An elevated CRP doesn't tell you what's inflamed, but it confirms that inflammation is present and gives your clinician a reason to look further.
One thing to keep in mind: CRP can be temporarily elevated after illness, injury, or even a hard gym session. A single unexpected reading is usually confirmed with a repeat test before anyone draws conclusions.
What your clinician is thinking
"Is there an underlying inflammatory process that could explain the fatigue, or contribute to other findings in this person's blood work?"
When everything comes back "normal" and you're still exhausted
This happens. More often than you'd think.
Normal results don't mean your fatigue isn't real. They mean the most common physiological contributors have been checked and they're not the primary issue. That's useful information, even if it doesn't feel satisfying. "We can rule out X, Y, and Z" isn't the answer you wanted, but it narrows the search.
Fatigue that persists despite clean blood work may involve sleep quality issues (including undiagnosed sleep apnoea), mental health conditions like depression or anxiety, chronic stress and burnout, medication side effects, or conditions like myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). The Australian Institute of Health and Welfare estimates ME/CFS affects around 219,000 Australians (based on ABS National Health Survey data).
There are also second-line blood tests your clinician might consider: cortisol (stress response), sex hormones (testosterone in men, oestrogen/progesterone in women), coeliac antibodies, or markers of autoimmune activity.
The point is: normal blood work is a stepping stone, not a dead end. Don't let "your results are fine" be the last conversation you have about it.
How to get results you can actually trust
Small things make a real difference to how useful your blood test results are, especially if you plan to track changes over time.
Fast when required. Some markers need an 8–12 hour fast for accurate results. Water is fine. Your order instructions will tell you if fasting is needed.
Test in the morning. Cortisol, testosterone, and other biomarkers follow a circadian rhythm. Morning testing — ideally before 10am — gives you the most consistent baseline.
Skip the hard session the day before. Intense exercise can temporarily shift CRP, liver enzymes, and other markers. A rest day before testing is worth it.
Don't test when you're properly unwell. A cold, infection, or gastro can throw off inflammatory and immune markers. Wait until you've recovered.
Be consistent across tests. Same time of day. Similar prep. Same lab method where possible. Trends are only meaningful if the conditions are comparable.
Tell your clinician everything you're taking. Iron supplements affect ferritin. Biotin supplements can interfere with thyroid assays. Certain medications shift blood sugar markers. Full disclosure gives cleaner data.
When you're ready, you can order online and attend a pathology collection centre near you. Find a location here.
Tests to consider through Bloody Good
If you want to cover the key fatigue-related markers, here's how the tests above map to the Bloody Good range.
| Test | What it covers | Category |
|---|---|---|
| Full Blood Count (FBC) | Haemoglobin, white blood cells, red blood cell indices | Core |
| Iron Studies (Including Ferritin) | Stored iron, circulating iron, transferrin saturation | Core |
| Thyroid Function Test (TFT) | TSH, Free T3, Free T4 | Core |
| Vitamin D (25-OH) | Vitamin D status | Core |
| Vitamin B12 | B12 levels | Core |
| HbA1c | 3-month blood sugar average | Core |
| High-Sensitivity CRP | Inflammation marker | Additional |
| Folate | Works alongside B12 | Additional |
| Cortisol | Stress hormone — worth considering if fatigue pairs with stress or sleep changes | Additional |
If you'd rather cover everything at once:
The Bloody Good Test covers 100 biomarkers in one test, including most of the markers above plus cholesterol, liver function, kidney function, and more. It's the broadest option if you want a full baseline rather than piecing together individual tests. If you're going to get your blood drawn anyway, you might as well get the full picture while you're there.
What to do once you've got your numbers
Blood test results are information, not a conclusion. Here's a practical approach to making them count.
Save your results. Testing is most useful when you can compare over time. The Bloody Good dashboard stores everything, which makes tracking straightforward.
Don't spiral over a single flag. One slightly out-of-range result can happen for all sorts of reasons: recent illness, hydration, supplements, time of day, biological variation. Context and trends matter more than isolated numbers.
Talk to your GP about anything that concerns you. They interpret results using your full clinical picture: symptoms, history, medications, risk factors. A lab report alone can't do that.
Start with the basics. If your results point to a nutritional gap or metabolic drift, the highest-leverage interventions are almost always the boring ones: consistent sleep, regular movement, balanced nutrition, stress management, moderating alcohol. They respond to nearly every marker in this article.
Retest with purpose. If you're making changes, retest in a timeframe that matches the marker. Iron stores take 2–3 months to shift meaningfully. HbA1c reflects the previous 2–3 months. Vitamin D typically needs 3 months of supplementation before a retest is informative. Your clinician can advise on timing.
If nothing shows up? Keep looking. Talk to your GP about second-line investigations. Consider a sleep study. Explore whether mental health support might help. "Normal blood work" isn't the same as "nothing is wrong." It just means the next answer is somewhere else.
Explore more biomarkers
If you want to go deeper into any of the markers covered here, the Bloody Good biomarker directory has detailed pages on what each test measures and how to think about results in general terms.
Browse the Bloody Good Biomarker Directory
This article provides general health information only and is not intended as medical advice, diagnosis, or treatment. Blood test results should be interpreted by a qualified healthcare professional in the context of your individual health circumstances, including symptoms, medical history, and medications. If you are experiencing persistent or concerning symptoms, consult your GP or seek medical attention promptly.