The first time I got comprehensive blood work back, I stared at the results for twenty minutes and understood almost nothing.
It was a table: dozens of rows, each with a marker name, a number, a unit of measurement, and a reference range. Some rows had an "H" next to them. One had an "L." The reference ranges looked arbitrary. The units were unfamiliar. And nobody had told me what to do with any of it.
This article is the guide I wish I'd had before I opened that first results email. How to read the report, what the numbers mean, when to be concerned, and when to take a breath and retest.
A note before we get into it
General information only. I'm not a pathologist. This article helps you understand the format and logic of blood test results. It does not replace clinical interpretation by your GP or specialist.
If you have results that concern you, discuss them with your clinician. Do not self-diagnose or self-treat based on blood test results alone.
What reference ranges actually are
Every marker on your results has a reference range: the values between which most healthy adults fall. Understanding what this range represents (and what it doesn't) is the foundation of reading your results.
How reference ranges are established: Labs test a large sample of apparently healthy people for each marker and calculate the range that captures the central 95% of results. The lowest 2.5% and highest 2.5% are excluded. These become the lower and upper limits of the reference range.
What this means practically: A reference range is a statistical construct, not a health guarantee. Being "in range" means you fall within the middle 95% of the population. It doesn't mean your level is optimal for you. Being "out of range" means you fall in the outer 5%, but 5% of healthy people are naturally outside the range. A single out-of-range result is not automatically a problem.
Why ranges vary between labs: Different labs use different equipment, methods, and reference populations. This is why the specific range printed on your results matters. Don't compare your number to a range from a different lab or a website using a different methodology.
"Normal" vs "optimal": Reference ranges tell you where most people sit. They don't tell you where the lowest-risk zone is. A ferritin of 15 ug/L is "in range" but functionally low. An HbA1c of 41 mmol/mol is "in range" but at the threshold of pre-diabetes. Reference ranges define the absence of obvious disease, not the presence of optimal health. I covered this distinction in detail in the biohacking article.
How to read flags and annotations
Most results reports use simple flags to draw attention to abnormal values.
H (High): Your result is above the upper limit of the reference range.
L (Low): Your result is below the lower limit of the reference range.
No flag: Your result falls within the reference range.
Critical flags (sometimes marked with asterisks or highlighted): Some labs flag results that are critically high or low, values that may require urgent attention. These are rare in routine screening but important when they appear.
A flag is an alert, not a diagnosis. It says "this number warrants attention." The clinical significance depends on how far out of range it is, whether it's consistent with previous results, and whether it correlates with symptoms or other markers.
A mildly elevated ALT (say 45 U/L with an upper limit of 40) is very different from a dramatically elevated ALT (say 300 U/L). Both get an "H" flag. Only one is urgent.
Why context changes everything
The same number can mean completely different things depending on who it belongs to and when it was measured. This is why self-interpretation has limits, and why your GP matters.
Age and sex. Reference ranges for many markers differ between men and women, and shift with age. Testosterone, ferritin, haemoglobin, and eGFR all have sex-specific and age-adjusted interpretation.
Time of day. Cortisol, testosterone, and iron are all influenced by circadian rhythms. A cortisol of 400 nmol/L at 8am is normal. The same level at midnight is not.
Fasting status. Triglycerides, glucose, and insulin are significantly affected by recent food intake. An elevated triglyceride reading after a meal is expected, not a flag for concern.
Medications. Statins affect liver enzymes. Metformin affects B12 absorption. Oral contraceptives affect SHBG, testosterone calculations, and thyroid binding proteins. Your clinician interprets results in the context of what you're taking.
Acute illness or stress. CRP, ferritin, white blood cell count, and cortisol can all be acutely affected by infection, injury, or stress. Testing while unwell produces results that reflect the acute state, not your baseline.
Recent exercise. AST, ALT, creatinine, and CRP can be temporarily elevated after intense training. Mentioning your exercise habits to your clinician prevents misinterpretation.
Hydration. Haemoglobin, haematocrit, and creatinine are affected by hydration status. Dehydration concentrates the blood and can produce falsely elevated results.
The lesson: never interpret a number in isolation. Always consider who, when, and under what conditions.
The pattern approach: reading results as a story
Individual markers are data points. Patterns are stories. Your GP reads the pattern, and you can learn to see it too.
The metabolic pattern: Elevated triglycerides + low HDL + elevated HbA1c + elevated fasting glucose + elevated fasting insulin = insulin resistance / metabolic syndrome. Each number individually might look borderline. Together, they tell a clear story. I covered this in the weight gain article.
The nutritional depletion pattern: Low ferritin + low B12 + low folate + low vitamin D = possible malabsorption (gut issue) rather than dietary inadequacy. This pattern should prompt investigation of gut function. See the gut health article.
The inflammatory pattern: Elevated CRP + elevated white blood cells + elevated ferritin (as an acute-phase reactant) = systemic inflammation. The source needs identification: infection, autoimmune, or metabolic.
The hormonal pattern: Elevated TSH + low Free T4 = hypothyroidism. Elevated testosterone + low SHBG + irregular periods = PCOS investigation warranted. Low testosterone + elevated LH + elevated FSH = primary testicular dysfunction.
The cardiovascular risk pattern: Elevated LDL + elevated triglycerides + low HDL + elevated HbA1c + elevated hs-CRP + reduced eGFR = high cardiovascular risk requiring comprehensive management.
You don't need a medical degree to see these patterns. You need the vocabulary (which this series has been building for 27 articles) and the awareness that patterns matter more than individual flags.
Common markers explained in plain language
Here's a quick-reference guide to the markers you'll most commonly encounter, organised by system.
Blood health: FBC (full blood count): haemoglobin (oxygen-carrying), white blood cells (immune), platelets (clotting), red blood cell indices (size and shape).
Iron: Ferritin (stored iron, the most important marker), serum iron, transferrin saturation, TIBC. Detailed: Article #3
Thyroid: TSH (the screening marker: high suggests underactive, low suggests overactive), Free T4, Free T3. Detailed: Article #6
Blood sugar: HbA1c (3-month average), fasting glucose (overnight snapshot), fasting insulin (early insulin resistance). Detailed: Article #8
Cholesterol: Total cholesterol, LDL (the one to manage), HDL (higher is generally better), triglycerides (respond to diet and alcohol). Detailed: Article #5
Liver: ALT and AST (liver cell damage markers), GGT (sensitive to alcohol), ALP (bile duct/bone), bilirubin, albumin. Detailed: Article #13
Kidney: eGFR (filtration rate, calculated from creatinine, adjusted for age and sex). Detailed: Article #22
Vitamins: Vitamin D (25-OH), Vitamin B12, Folate.
Inflammation: CRP or hs-CRP (systemic inflammation marker, nonspecific but broadly useful). Detailed: Article #10
Hormones: Testosterone, SHBG, FSH, LH, oestradiol, cortisol, DHEAS. Interpretation depends heavily on clinical context, sex, and age.
When one abnormal result matters, and when it doesn't
Probably significant
A result that's far outside the reference range (not just mildly above or below).
A result that correlates with symptoms you're experiencing.
A result that forms a pattern with other abnormal markers.
A result that's changed significantly from a previous test.
A critical flag.
Probably not immediately significant
A mildly out-of-range result with no symptoms and no pattern.
A result affected by known confounders (exercise, timing, hydration, acute illness).
A single borderline result that hasn't been confirmed with repeat testing.
The rule of thumb: mildly abnormal results in asymptomatic people usually warrant monitoring (retest in 4-12 weeks) rather than immediate intervention. Significantly abnormal results or results that correlate with symptoms warrant prompt discussion with your GP.
How to track results over time
This is the habit that turns blood testing from a snapshot into a trajectory, and trajectories are what drive meaningful health decisions.
Save every result. Whether digital or paper, keep a record. Bloody Good results are stored in your account for future comparison.
Create a simple tracking spreadsheet. Date, key markers, values. Focus on the markers most relevant to your health picture. For most people: ferritin, vitamin D, HbA1c, cholesterol panel, and thyroid (TSH) are the core trackers.
Test under consistent conditions. Same time of year, fasted, morning, rested. This reduces variability and makes comparisons meaningful.
Look at trends, not single numbers. HbA1c rising from 30 to 34 to 37 over three years is a trend, even though every number is "in range." Ferritin dropping from 80 to 50 to 25 is a trend. These trajectories matter more than any single reading.
Share your history with your GP. When you bring three years of results to a consultation, your GP can see the story, not just the snapshot.
When to discuss results with your GP
Always discuss results with your GP if:
Any marker is flagged (H or L).
You have symptoms that might relate to the results.
You're on medications that affect blood markers.
You've noticed a trend over multiple tests.
You're not sure what a result means.
It's reasonable to wait and retest if:
A single marker is mildly out of range, you're asymptomatic, and there's a plausible explanation (recent illness, exercise, dietary changes). Or the result is borderline and your GP has previously indicated monitoring rather than intervention.
See your GP promptly if:
Results are critically flagged.
You have new or worsening symptoms alongside abnormal results.
Your GP has specifically requested you follow up after testing.
How Bloody Good results work
Bloody Good results are delivered digitally through your account. Every test is reviewed by an Australian-registered doctor. Your results include reference ranges specific to the laboratory that processed your sample, and a doctor's commentary where relevant.
Results are not a diagnosis. They are data, reviewed by a doctor, delivered to you, and intended to be discussed with your GP for personalised clinical interpretation and management.
You can access previous results through your account for comparison over time. This built-in history makes longitudinal tracking easier than managing paper reports from different pathology providers.
For a complete overview of what's available: Browse all Bloody Good blood tests
The most important thing about your results
Your blood test results are a snapshot of your internal environment at one point in time. They're valuable. They're informative. They can reveal things you'd never have known otherwise: a low ferritin, a creeping HbA1c, a thyroid that's drifting.
But they're not a verdict. They're not a diagnosis. And they're not a substitute for the conversation with your GP that puts them in context.
The best use of blood test results is this: understand the basics (which this article helps with), notice the patterns (which this series has been teaching), track over time (which makes every future test more valuable), and discuss with your clinician (who adds the context that numbers alone can't provide).
That combination, your data, your awareness, your clinician's expertise, is how testing translates into better health decisions.
Explore more biomarkers
Browse the Bloody Good Biomarker Directory
General information only. This article is not medical advice and is not a substitute for care from a qualified health professional. If you have concerning symptoms or urgent health issues, seek medical attention promptly.