Why are some values printed in red on my report?
Red usually marks a result that sits outside the reference range, so it stands out at a glance. Some labs also use red for a critical value. That is a result far enough outside the range that the lab flags it for urgent attention [CLSI, 2010]. Red is a visual cue, not a diagnosis.
Last reviewed: 2026-08-16
What does a red value usually mean?
Most often, red simply means the value is outside the range, the same idea as an H or L flag.
It helps you and your doctor find the out-of-range results quickly on a busy page.
What is a critical value?
A critical value is a result so far outside the range that it may need prompt action. Labs keep a list of these and often call the doctor directly [CLSI, 2010].
If a value is critical, it is worth contacting your doctor without delay.
Does red always mean something serious?
No. Many red values are only mildly outside the range and are not urgent.
The colour tells you where to look. Your doctor tells you what it means for you.
Frequently asked questions
- Is every red value a critical value?
- No. Red often just marks any out-of-range result. Only a small set of far-out values are true critical values.
- Should I panic if I see red?
- No. Note the red values and discuss them with your doctor. Context decides what, if anything, to do next.
- Why is one red value worse than another?
- How far a value sits outside the range, and which test it is, both matter. Your doctor weighs these together.
- Do all labs print in red?
- No. Some use bold, an asterisk or a separate column instead. The purpose is the same: to highlight out-of-range results.
Sources
- CLSI (2010) — Clinical and Laboratory Standards Institute (reference intervals, methods, specimen handling)
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