H, L and asterisks on a lab report: what the flags tell you
Read the result, unit and laboratory range together before turning a highlighted number into a conclusion about your health.
Medicod · Published
Prepared with AI assistance using the sources listed below. General information, not an individual clinical assessment.
Start with the report’s own key
An H often marks a result above the laboratory’s reference range; an L often marks one below it. Some reports use an asterisk, arrow or color instead. Check the legend on your document, because a symbol can also point to a laboratory comment.
A flag draws attention to a result. It does not, by itself, name a disease or decide whether treatment is needed. A result within range also cannot rule out every health problem. The reason for testing, symptoms and medical history remain part of the interpretation.
Read one complete row
Keep the test’s exact name, result, unit, reference range and comments together. A number without a unit can be misleading. A value written as “greater than” or “less than” a number is not an exact measurement at that boundary.
For example, a result marked “>100” should not become 100 in your notes. That change creates precision the report does not contain. Similarly, an empty field does not mean zero or negative.
Use the range from the laboratory that tested you
Laboratories can use different methods and reference ranges. A range from a search result, a friend’s report or a different laboratory may not apply to your sample. Check age-related or other qualifications printed beside the range.
If you are comparing earlier results, preserve each report’s original range. Do not replace all the ranges with the newest one to make a spreadsheet look consistent. Your clinician can explain which comparisons are meaningful.
Add what the report cannot show
Write down why the test was ordered, any relevant symptoms and whether preparation differed from the instructions. Food, strenuous exercise and some medicines can affect certain tests. Report what actually happened; do not assume that a possible influence explains the entire result.
Bring a current medication and supplement list. Do not stop a prescribed medicine to remove a flag or start a supplement solely because a number is highlighted.
Ask for a next step, not just a label
Useful questions include: “Which other results should we read with this one?”, “Does this need confirmation?” and “When should I follow up?” Keep the answers with the original report.
If the laboratory or clinician contacts you about an urgent result, follow that instruction promptly. General explanations of flags cannot determine urgency. When using an automated explanation, verify the extracted row against the original first, especially the decimal point, unit and comparison signs.