How to Read a Blood Test

I put this together because I found myself repeating the same explanations across multiple consultations. Writing it down means the knowledge can spread further.

Before we can start though, you need to know that 90% of the reference ranges on your blood test are population-based, not optimal-health-based. There are exceptions; diabetes and kidney failure diagnostic criteria are consensus-based, but most nutrient ranges are set to prevent disease, not to support optimal health.

Here are some of the key markers.

 

The Inflammation Marker  – C R P

Ideally your CRP should be under 1 mg/L. Most labs will flag anything under 5 or 7 mg/L as “normal”. That threshold is too high unless you have a known chronic condition.

CRP (C-reactive protein) is a nonspecific marker that rises with infection, cancer, or injury. A result sitting at 3–4 mg/L signals low-grade chronic inflammation, commonly driven by obesity or smoking. This matters because inflammation accelerates ageing and raises your risk of chronic disease.

 

Vitamin D

Sourced mainly from sunlight and a little from diet. Essential for bone strength, hormone production, and immune function.

Most labs set “normal” above 50 nmol/L. That’s outdated. The correct target is above 70 nmol/L — especially at the end of summer, when you need reserves for bone protection through winter. Levels commonly drop by 30 points over winter, so supplementation is often necessary. For optimal immune protection, aim above 150 nmol/L; this was the consistent message from multiple presenters at the 2025 ACNEM conference.

 

Vitamin B12

Standard B12 should be over 400 pmol/L. If it comes back below 400, 360, or 260 (the cutoff varies by lab), the lab will run active B12 (holotranscobalamin). This must be above 100 pmol/L — B12 is used in every cell in your body, and it protects your brain by maintaining the myelin sheath around nerve cells.

Labs flag deficiency below 35 pmol/L. Don’t be fooled, 36 pmol/L is not “fine.” It’s a slide, not a cliff edge. People consistently report less fatigue once active B12 sits above 100 pmol/L.

Optimal B12 also improves iron retention, critical for many perimenopausal women.

Best food sources: red meat and dairy. Vegetables contain no B12, but support the absorption of the B12 you do eat.

 

Electrolytes and Liver Enzymes

Bicarbonate ideally should be over 27 mmol/L, this partially reflects your acid-base balance. Chronic acidity leaches calcium from your bones over time, driving osteoporosis. Improve it with vegetables, stress management, and adequate vitamin D.

AST and ALT should sit in roughly a 1:1 ratio. A skewed ratio, or elevated numbers, suggest a fatty liver. Don’t accept “40 U/L is normal” as “40 U/L is healthy”. These ranges shift by lab, region, and have increased over time with our weight. The real target is under 20 U/L, which is where most people sat before processed food reshaped our diets in the decades since the 1970s.

 

Thyroid

TSH (Thyroid Stimulating Hormone) is the standard first-line test. There is no universal consensus on the ideal non-pregnant range. Given pregnancy guidelines set the target under 2.5, I generally suggest that threshold should apply to everyone. Other integrative doctors have even stricter guidelines.

Free T4 and free T3 give a clearer picture of thyroid function and the feedback loop, but Medicare won’t cover them unless TSH is abnormal or thyroid disease is already diagnosed.

Thyroid antibodies are worth ordering if there’s a family history, as they reveal thyroid-specific inflammation.

 

Iron Studies – ferritin, saturation, and iron

Iron should never assessed from one number — it’s a panel, and ferritin, transferrin saturation, and serum iron each tell a different part of the story.

Ferritin reflects your stored iron. Australian labs typically report “normal” above 30 µg/L. For genuine hormonal, energy, hair, and cognitive support, aim for ferritin above 50 µg/L. The closer to 100 µg/L the better, if you’re able to get there.

Transferrin saturation tells you how much iron is actually available for your cells to use right now. Below 20% can mean iron isn’t reaching your tissues, regardless of what your ferritin says. Above 45%, with raised ferritin, suggests iron overload and warrants haemochromatosis screening.

 

HbA1c

HbA1c gives you an average of your blood glucose over the past 8–12 weeks.

In Australia, it’s currently reported in mmol/mol and a % side by side. A result of 48 mmol/mol (6.5%) or above confirms diabetes. For genuine metabolic health, you want your HbA1c comfortably below 35 mmol/mol (around 5.4%) as this is where insulin resistance, weight gain, and long-term vascular damage, are less likely.
The issue is the area between these two values. For many doctors this is still considered normal. If your HbA1c is creeping up year on year, even while staying inside the “normal” range, that trend matters more than the single number. Pair it with fasting insulin for the full picture.

 

Glucose and Insulin

Fasting glucose alone tells you half the story. Fasting insulin reveals how hard your body is working to keep glucose in range. Your glucose should be under 10 mU/L.
The gold standard is a glucose tolerance test with insulin, tracking your response to a sugar load over two hours. It’s a much bigger commitment, but also gives the clearest picture of how your metabolism is actually functioning.

Elevated insulin means your sugar and carbohydrate intake need immediate attention. Your body is working hard to keep the sugar levels stable by raising insulin levels, but left unaddressed, this is the direct path to type 2 diabetes. 

 

Finally

There’s more depth available, but this covers what you can assess yourself from a standard GP blood panel.

And of course, this is meant for education, not diagnosis!