Lab result flags (H, L, A and others): what the flag column records
A flag is the lab's own short mark beside a result: typically H for above an upper limit, L for below a lower limit, and A for abnormal on results that are not numbers. It records where a result sat against a limit the lab applied. It does not say what the result means for a person.
Not medical advice. This guide describes what the parts of a lab report are and how they are recorded. It does not say what any result means for a person, and it does not recommend treatment, supplements or targets.
What the flag column records
Many lab systems send results with the HL7 abnormal-flag codes: L and H for below the low or above the high normal limit, LL and HH for beyond lower or upper critical (panic) limits, N for normal, and A or AA for abnormal and very abnormal results that are not numbers, such as a positive test. Further codes mark a significant change since a previous result, U for up and D for down. A report may show these as letters, words, arrows or asterisks.
The flag usually comes from comparing the result with a reference interval or critical limits held in the lab's system. That interval may be one of several, chosen by age and sex, while the report prints only one of them or writes the range as text. A flag and a printed range can therefore disagree without either being wrong.
A missing flag is not a flag. Some labs mark only results outside their limits, others print N or leave the cell blank, and some layouts show the mark only by column, such as Out of Range. Record what is printed, and note when nothing is.
Recording flags
Five steps.
Find where the flag sits
Look in a Flag column, after the result (131 H), before it, as an arrow or asterisk, or as a word. Check layouts with In Range and Out of Range columns.
Copy it as printed
Store the lab's mark in its own column exactly as shown. Standardise to H and L only in a second column.
Keep it apart from your own comparison
If you compare value and range yourself, store that in a separate column and never overwrite the lab's mark.
Note when they differ
Banded ranges, sex and age bands, an inclusive or exclusive limit, or an unprinted limit can all make a lab flag differ from a simple comparison. Record both.
Leave blanks blank
No flag means none was printed. Do not fill the cell with a normal mark.
Flag marks and how they are recorded
The third column is how BioPanel stores the lab's mark.
| Mark as printed | Stored as | What it records |
|---|---|---|
| H, High, Above, ↑, ▲ | H | Above the upper limit the lab applied |
| L, Low, Below, ↓, ▼ | L | Below the lower limit the lab applied |
| HH, Critical high, Panic high | HH | Beyond an upper critical (panic) limit |
| LL, Critical low, Panic low | LL | Beyond a lower critical (panic) limit |
| A, AA, Abn, Abnormal, Out of range, * | A | Marked abnormal, typically on results that are not numbers |
| N, Normal, WNL, In range | N | The lab marked the result as normal |
| Anything else, such as U, D, B or W | Kept, in capitals | A lab-specific or HL7 code, for example a significant change since a previous result |
What goes wrong
Most come from asking a flag to do more than it records.
- Reading a flag as a diagnosis. A flag records position against a limit. It does not say what a result means for a person.
- Overwriting the flag with your own. Keep the lab's mark and your comparison in separate columns, so a difference stays visible.
- Assuming no flag means in range. Some labs flag nothing, and a blank can also mean the layout has no flag column.
- Missing a flag that is a column. In a layout with an Out of Range column, the column is the mark and there may be no letter.
- Comparing with the wrong band. If the report prints men's and women's ranges, the lab's flag used the one for the sample. Yours may not.
- Ignoring the limit's sign. A result equal to a limit may or may not be flagged, depending on whether the limit is inclusive. Keep the sign printed in the range.
How BioPanel helps
BioPanel stores the lab's flag in lab_flag, shortened to H, L, HH, LL, A or N as in the table, or kept in capitals if it is something else. It also fills computed_flag by comparing the value with the range printed on the same report, and leaves it blank when no fair comparison is possible: no range, several bands, or sex and age groups. When the two disagree it shows a warning that lists the markers. A result in an Out of Range column with no mark gets the lab flag A. Neither column says what a result means. Upload a lab report PDF or photo to see them side by side. Free: 1 file per day, up to 10 pages, no account. Files over 10 pages are converted up to page 10 on the free allowance; a page code converts the whole file, up to 150 pages. See pricing.
Questions people ask
What do H and L mean on a lab report?
H marks a result above the upper limit the lab applied and L one below the lower limit. They record position against a limit, not what the result means for a person.
What is the difference between H and HH?
HH, and LL at the other end, typically mark results beyond a critical (panic) limit, which sits further out than the usual limits. Not every report prints those limits.
What does A mean as a flag?
Abnormal. It is typically used for results that are not numbers, such as a positive, and some labs use it for any result outside the printed range.
Why does a flag disagree with the range I can see?
The lab may have applied a band for age or sex that the report does not print, critical limits, or another limit than the one shown. Record both and ask the lab.
Does no flag mean a result is normal?
Not by itself. Some labs print nothing for results inside their limits, others print N, and some layouts have no flag column. Leave the cell blank when nothing is printed.
Does a flag tell me what to do?
No. A flag is the lab's mark of position against a limit. What a result means for you is for a clinician who knows your history. This is not medical advice.