Lab Values — Normal Ranges in Plain Language

Each laboratory establishes its own reference range using its instruments, methods and the population it serves — so the same test can carry a slightly different range at a different lab, and ranges also differ between countries that use different units. That is why the range printed on your own report is the correct one to compare your result with, and why the values here are labelled typical adult ranges rather than exact cut-offs.

Reference ranges are usually built to include the results of about 95% of healthy people — which means about 1 in 20 healthy people will fall slightly outside on any given test, and the more tests in a panel, the more likely one flags borderline. A mildly abnormal result is often repeated before any conclusion is drawn, and clinicians interpret it alongside your symptoms, history and previous results rather than alone.

Most United States laboratories report in conventional units (for example milligrams per decilitre, mg/dL), while many other countries report in SI units (for example millimoles per litre, mmol/L). They describe the same measurement in different scales. Each test page in this guide shows the typical range in both systems where the two differ.

Some measurements naturally differ by sex — hemoglobin and creatinine are familiar examples, because they track with muscle mass and red-cell mass. Where that applies, the test page states both ranges. Ranges can also differ by age, and most ranges here are for adults; children’s ranges are often quite different and are not covered by this guide.

Some tests are affected by recent food — glucose and triglycerides are the classic examples — and the test pages note fasting where it applies. Many other tests need no preparation at all. Follow the instructions given when your test is booked, and mention any medicines and supplements you take, because some (such as the vitamin biotin) can interfere with certain laboratory methods.

Only in general terms. Each test page describes, in plain language, the kinds of situations a high or low result can be associated with — it cannot say which applies to you. The same abnormal value can have many causes, and your clinician interprets the pattern of results together with your examination and history. If a result worries you, that conversation is the right next step.