A common message from new members: one number on an old report was flagged, and they want to know if it is serious. The honest answer is usually that one number cannot tell us.

Why single markers mislead

Every marker has three problems. It varies from day to day, sometimes by 10 to 20 percent. It can be raised for reasons that have nothing to do with disease. And it can look normal while the process it is meant to track is already under way.

• Ferritin rises with iron stores, but also with inflammation, alcohol and fatty liver.
• ALT can stay raised for a week after a hard gym session.
• TSH changes with the time of day and with recent illness.
• HbA1c reads low in anyone whose red cells turn over quickly, including some endurance athletes.

A single result is a question. A pattern is an answer.

How a panel corrects itself

Read together, markers cover each other's blind spots. A high ferritin with a normal CRP and normal liver enzymes points to iron. The same ferritin with a high CRP points somewhere else. A borderline HbA1c next to a fasting insulin of 4 is reassuring. Next to an insulin of 15 it is not.

What our baseline includes

Our baseline panel has 48 markers across seven systems: cardiovascular, metabolic, liver, kidney, thyroid, inflammation and blood count. Each is reported against our target range, not only the lab's, and each is shown next to the markers it is usually read with.

Repeat before you react

When one result sits out of line with the rest, we repeat it before changing anything. Over the last year about a third of isolated abnormal results came back in range on a second sample four to six weeks later. Acting on the first reading would have meant treating noise.