How to Read Your Blood Test Results
A step-by-step guide to understanding what your numbers mean, so you can have better conversations with your doctor.
Anatomy of a Blood Test Report
Every blood test report follows a similar structure. Understanding the layout makes it much easier to interpret your results. Here is what a typical row on a lab report looks like:
Sample result from a typical pathology report:
| Test Name | Result | Units | Reference Range | Flag |
|---|---|---|---|---|
| Total Cholesterol | 6.8 | mmol/L | < 5.5 | H |
| HDL Cholesterol | 1.4 | mmol/L | > 1.0 | |
| Haemoglobin | 108 | g/L | 120 - 160 | L |
Test Name / Marker
The specific substance or measurement being tested. For example, "Total Cholesterol" or "Haemoglobin". Some labs use abbreviations like HbA1c or eGFR.
Your Result
The numeric value measured from your blood sample. This is the number you compare against the reference range.
Unit of Measurement
The unit tells you what scale the number is measured in. The same marker can appear in different units depending on the country or lab.
Reference Range
The range of values considered normal for a healthy person. If your result falls within this range, it is generally not a concern.
Flag
A letter or symbol indicating your result is outside the reference range. H means high, L means low, and * or A means abnormal.
Understanding Reference Ranges
Reference ranges are the backbone of blood test interpretation. But they are not as simple as they first appear.
A reference range is established by testing a large group of healthy people and finding the middle 95% of results. This means that 5% of perfectly healthy individuals will naturally fall outside the range. Having a result outside the range does not automatically mean something is wrong.
Why ranges differ between labs
Different laboratories use different testing equipment, reagents, and methodologies. A cholesterol result from Lab A may not be directly comparable to Lab B. This is why your report always includes the specific reference range for the laboratory that performed your test. When tracking trends over time, it is best to use the same lab whenever possible.
Age and gender differences
Many markers have different normal ranges depending on age and sex. Haemoglobin, for example, has a reference range of 130 to 170 g/L for adult males and 120 to 150 g/L for adult females. Creatinine, testosterone, and iron studies also vary significantly. Children and older adults often have their own separate ranges.
Reference range vs. optimal range
A value within the reference range is statistically normal, but "normal" and "optimal" are not the same thing. For example, a fasting glucose of 5.9 mmol/L is technically within the reference range (3.0 to 6.0) but sits at the very top. Many practitioners consider an optimal fasting glucose to be below 5.0 mmol/L. Similarly, a Vitamin D level of 51 nmol/L meets the reference minimum of 50, but optimal levels are generally considered to be 75 to 150 nmol/L.
The Flag System
Flags are the quickest way to spot results that need attention. Here is what each flag means:
High
Your result is above the upper limit of the reference range. Common causes include diet, dehydration, medications, or an underlying condition.
Critical High
Your result is significantly above the reference range and may require urgent attention. The lab will typically notify your doctor directly.
Low
Your result is below the lower limit of the reference range. This could indicate a deficiency, dilution effect, or an underlying condition.
Critical Low
Your result is dangerously below the reference range. This is considered a critical value, and your doctor will be contacted by the laboratory.
Abnormal
A general flag indicating the result is outside the expected range. Some labs use A or an asterisk instead of H or L.
No Flag (Normal)
No flag means your result falls within the reference range. This is the outcome you want to see for most markers.
Reading Your Results: 5-Step Method
Follow this method every time you receive a new blood test report. It takes less than five minutes and gives you a clear picture of where you stand.
Check the date
Verify you are looking at your most recent blood test. Older results may no longer reflect your current health status.
Look for flags first
Scan the flag column for H (High), L (Low), or * (Abnormal) markers. These highlight results that fall outside the reference range.
Compare to reference ranges
For each flagged result, check how far outside the range it is. A value just slightly outside is very different from one that is double the upper limit.
Look at trends over time
Compare this test to previous results. A single abnormal value matters less than a consistent trend in the wrong direction.
Consider the context
Think about symptoms, medications, recent illness, fasting status, and lifestyle changes that could explain abnormal values.
Common Units Explained
Blood test results use a variety of measurement units. This table explains the most common ones you will encounter on Australian and international pathology reports.
| Unit | Full Name | Commonly Used For | Example |
|---|---|---|---|
mmol/L | Millimoles per litre | Cholesterol, glucose, electrolytes (sodium, potassium) | Total Cholesterol: 5.2 mmol/L |
g/L | Grams per litre | Proteins (albumin, total protein), haemoglobin | Albumin: 42 g/L |
U/L | Units per litre | Enzymes (ALT, AST, ALP, GGT) | ALT: 28 U/L |
pmol/L | Picomoles per litre | Thyroid hormones (Free T4, Free T3) | Free T4: 15.2 pmol/L |
µmol/L | Micromoles per litre | Creatinine, bilirubin, uric acid, iron | Creatinine: 82 µmol/L |
x10⁹/L | Billions per litre | Blood cell counts (white cells, platelets) | White Blood Cells: 6.8 x10⁹/L |
% | Percentage | HbA1c, haematocrit, differential white cell count | HbA1c: 5.4% |
mL/min | Millilitres per minute | eGFR (estimated kidney filtration rate) | eGFR: 92 mL/min/1.73m² |
When to Be Concerned
Not all abnormal results carry the same weight. Here is a practical guide to understanding how urgently you should act.
A result that is only slightly outside the reference range is usually not cause for alarm. Many healthy people occasionally have a value that sits just above or below the range. Your doctor may suggest retesting in 3 to 6 months to see if it returns to normal on its own. Lifestyle factors such as diet, hydration, exercise, and sleep can all cause mild fluctuations.
When a result is clearly outside the reference range, it is worth discussing with your doctor within 1 to 2 weeks. A moderately abnormal result does not necessarily indicate a serious condition, but it does warrant further investigation. Your doctor may order additional tests to understand the cause, or may recommend dietary or medication changes.
Critical values are results that are so far outside the normal range that they may pose an immediate health risk. Laboratories will usually contact your doctor directly when a critical value is detected. If you see a result flagged as HH (critical high) or LL (critical low), contact your healthcare provider the same day. Examples include very low haemoglobin, dangerously high potassium, or extremely elevated liver enzymes.
When several markers are abnormal at the same time, it may indicate an underlying pattern. For example, elevated ALT and AST together suggest liver involvement. High glucose combined with elevated HbA1c points toward diabetes management issues. Multiple abnormalities are a stronger signal than any single result and should be discussed with your doctor promptly.
Why Tracking Over Time Matters
A single blood test is a snapshot. Multiple tests over time tell the full story of your health.
Imagine you receive a cholesterol result of 5.5 mmol/L, which is at the upper end of the desirable range. Is this good or bad? The answer depends entirely on what came before:
Concerning trend
Last year: 4.2 mmol/L. This year: 5.5 mmol/L. That is a 31% increase in 12 months, suggesting a worsening trajectory that deserves attention.
Reassuring trend
Last year: 6.8 mmol/L. This year: 5.5 mmol/L. That is a 19% improvement, showing your lifestyle changes or medication are working.
This is exactly why SmarterBlood plots your results on graphs over time. Trends reveal what static numbers cannot: whether your health is improving, stable, or declining.
- Gradual improvement over 3 or more tests is a strong positive signal
Even if individual values are still slightly out of range
- Stable results within range confirm ongoing good health
Consistency is just as valuable as any single perfect number
- A steady decline over multiple tests warrants a conversation with your doctor
Even if each individual result is still technically within range
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