How to compare two blood tests
Updated
Short answer
Put both results in the same unit, read each against the range printed on its own report, and look at the size of the change as well as where each value sits. Differences in lab, method, fasting status and time of day can matter as much as a real change.
Step 1: Put both results in the same unit
Check the unit on each report before comparing numbers. A total cholesterol of 5.0 and one of 193 can be the same result written in two units (mmol/L and mg/dL). Convert one to the other with a standard factor. The unit converter does this for 54 markers and shows the factor it used.
Step 2: Read each result against its own range
Each report prints a reference range for its lab and method. Compare each value with the range from the same report, not with a range from another lab or one you found online. A value can be below, within or above the range printed on one report and sit differently against another lab's range.
BiomarkerHQ labels a result only as below, within or above the range printed on your report. It says nothing about what that position means.
Step 3: Look at the size of the change
Two numbers can be compared two ways. The absolute change is the later value minus the earlier one. The relative change divides that by the earlier value.
change = B − A
relative change (%) = (B − A) ÷ A × 100
| Marker | Draw A | Draw B | Change | Relative change |
|---|---|---|---|---|
| ApoB | 98 mg/dL | 82 mg/dL | −16 mg/dL | −16.3% |
| Testosterone (total) | 14.8 nmol/L | 17.8 nmol/L | +3.0 nmol/L | +20.3% |
| Glucose (fasting) | 5.1 mmol/L | 5.3 mmol/L | +0.2 mmol/L | +3.9% |
A small change can sit inside the variation of the test itself: the same sample measured twice does not give identical numbers, and a person's own values drift from day to day. How large a change has to be to matter depends on the marker and the person. That is a question for a qualified clinician.
Step 4: Check what was different about the two draws
- Lab and method. A different analyser, or a calculated against a measured value, can shift a result.
- Fasting status and time of day. Glucose, triglycerides and cortisol are examples of markers where this matters.
- The weeks before. Illness, travel, unusual training or a change to supplements can all show up.
- The unit and the range. Confirm both reports use the unit you think they do.
What a comparison cannot tell you
Comparing in BiomarkerHQ
The compare panel puts two draws side by side, the older as A and the newer as B, with the change for each marker and the largest movers first. For each draw it also shows the averages of your wearable data (HRV, resting heart rate, sleep and temperature) for the 30 days before it, and how many of those days had data, so context is there without any interpretation being added.
Frequently asked questions
What counts as a meaningful change between two blood tests?
There is no single answer. It depends on the marker, how it is measured and the person. Ask a qualified clinician. BiomarkerHQ shows the size of the change and does not judge it.
Can I compare results from two different labs?
You can, with care: convert units, read each result against its own report's range, and allow for differences in method between labs.
Why does my result look different when the unit changed?
Because the number depends on the unit. Convert both results to one unit and compare again.
How many draws do I need to see a trend?
Two draws show a change. Three or more show a direction more clearly, and wearable data between draws adds context. There is no fixed number.
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