Laboratory tests (analyses) are the measurement of parameters in blood, urine and other biological samples. They help detect diseases at an early stage, refine a diagnosis, monitor treatment and assess risks — many subclinical conditions are visible only through tests.
The result is almost always compared with a reference interval — the range of values typical of healthy people. Falling outside its limits does not necessarily mean disease, and a test should be interpreted together with a doctor.
What kinds there are
Blood biochemistry assesses metabolism and organ function (glucose, cholesterol, liver and kidney markers — ALT, creatinine). The complete blood count shows haemoglobin, white cells and platelets. Separate groups are hormones (TSH), vitamins and minerals (vitamin D, calcium, ferritin).
Besides blood, urine is examined (urinalysis), and microbiological and molecular methods are used (cultures, PCR).
What a reference interval is
A reference interval is the range of values in most healthy people. It depends on the instrument, the method, and also on age and sex, so norms differ between laboratories.
By the very nature of the interval, about one in twenty healthy people has a result outside its limits. So a small deviation does not equal disease — what matters is the magnitude, the trend and the overall clinical picture.
How to test correctly and what distorts it
Many tests are taken on an empty stomach (glucose, lipids); some depend on the time of day (cortisol, iron). Results are affected by medicines and supplements — for example, biotin distorts some hormone tests — as well as by exercise the day before and the phase of the cycle.
For results to be comparable, take repeat tests where possible in the same laboratory and by the same method.
Calculate using this marker
Calculators where Laboratory tests is used directly:
Frequently asked questions
What does a result "outside the range" mean?
A reference interval covers the values in most healthy people, so some healthy people by definition fall outside its limits. A small deviation is often not dangerous; what matters is the size of the deviation, the trend and the clinical picture — assessed by a doctor.
Why do norms differ between laboratories?
Laboratories use different instruments, reagents and methods, so their reference intervals are their own. Rely on the norms of the laboratory where you were tested and, where possible, track the trend in one place.