Common questions
What does out of range actually mean?
Reference ranges are built to include the middle 95% of a healthy population, which means one in twenty healthy people falls outside by definition. A result just outside the range, with no symptoms, usually means very little. A result inside the range can still be wrong for you — ferritin is the clearest example.
Why do ranges differ between laboratories?
Because each laboratory sets ranges for its own equipment, methods and local population. This is why comparing a result against a range printed on a different report is unreliable, and why serial results from the same laboratory tell you far more than a single value.
Which results should I never wait on?
Potassium far outside range, very low hemoglobin, markedly abnormal liver enzymes, and a very high calcium. Any laboratory will phone these through as critical values — if a result is genuinely urgent you will usually hear about it before you see the report.
Does timing affect the numbers?
Considerably. Cortisol swings across the day, iron studies are affected by a recent meal and by supplements, thyroid results shift with the timing of levothyroxine, and lipids used to require fasting though most guidelines no longer insist on it. Sex hormones depend heavily on cycle day.