Reference change value (serial lab results)
Reports whether a change between two results on the same patient is a real one.
Open the calculator → Runs in your browser. Data leaves only if you deliberately send a problem report from the interactive tool.
Example
- Analytical imprecision, from the laboratory
- 2.2 CV %
- Within-subject biological variation, from published tables
- 4.4 CV %
- Probability and sidedness
- Two-sided, 95% - a change in either direction
- Previous result, to compare against the current one
- 1.0
- Current result
- 1.08
Result: a change that does not exceed the reference change value, which is not the same as stable
The tool opens with these values already filled in. Replace them with your own.
What the result means
- The formula
- Square root of 2, times the probability factor, times the square root of the analytical CV squared plus the within-subject CV squared.
- The factor
- 1.96 two-sided at 95%, 1.65 one-sided at 95%, 2.58 two-sided at 99%, 2.33 one-sided at 99%.
- Below it
- Not stable. A change that cannot be told apart from analytical and biological variation, which is a different statement.
- Above it
- A real change, and not necessarily an important one. The arithmetic answers whether something moved.
- The inputs
- Analytical imprecision belongs to the assay; within-subject variation is a property of the analyte and comes from published tables.
- The assumption
- A steady state. Across an acute illness, a transfusion or a dose change, the published within-subject variation is not the variation in front of you.
What you enter
- Analytical imprecision, from the laboratory
- Within-subject biological variation, from published tables
- Probability and sidedness
- Previous result, to compare against the current one
- Current result
How this is calculated
Fraser CG, Harris EK. Generation and application of data on biological variation in clinical chemistry. Crit Rev Clin Lab Sci. 1989;27(5):409-437. Fraser CG. Reference change values. Clin Chem Lab Med. 2011;50(5):807-812. Read the sources: Fraser 1989 ↗, Fraser 2011 ↗
A reference and educational tool. Not medical, legal, or financial advice, and not a substitute for clinician judgment.