How to understand your tests

Why we do tests

Laboratory tests help with:

• diagnosis — to confirm or rule out a disease
• monitoring — to follow a known disease or the effect of treatment
• screening — for certain diseases (e.g. diabetes, cholesterol), in certain groups

There is no “package that rules out everything”

We are often asked for “complete tests” to be sure that everything is fine. In reality, no package rules out all diseases. Moreover, unnecessary tests:

• can give slightly out-of-range results in perfectly healthy people (statistically, about 1 in 20 values)
• cause anxiety and lead to further, often unnecessary, examinations

That is why the doctor chooses tests according to age, risk and the specific concern. A good check-up is personalized.

Preparation

• Not all tests require fasting. Ask beforehand about food, fluids and timing.
• Water is usually allowed.
• Do not stop your medicines yourself — unless you have been asked to.
• Tell the staff about supplements (especially biotin), recent antibiotics and pregnancy.

For practical guidance, see the page How to give samples correctly for testing.

How to read the results

Reference range (“normal values”)

The reference range represents the values of 95% of healthy people. This means:

• A value outside the range is not in itself a diagnosis.
• A value within the range does not rule out every disease.
• Ranges differ according to the laboratory, method, age and sex. Always compare with the range printed on your own report.

Change over time

The trend is often more important than a single value. Keep previous results and bring them to your visit.

Critical results

Some values (e.g. very high potassium, very low glucose) are considered critical and the laboratory must tell you immediately. If you are phoned about such a result, follow the instructions without delay.

Tumor markers — caution

Markers such as CA 15-3, CA 19-9, CA 125 or CEA are not tests to detect cancer in people without symptoms. They are used in specific contexts, mainly for following patients with known cancer. See CA 15-3.

Sample quality

Correct identification, the right container, time of collection, storage and transport affect reliability. Some specialized tests are sent to reference laboratories; ask about the turnaround time.

Interpretation by the doctor

Results make sense only together with your history, symptoms and examination. If you have tests done elsewhere and are not sure what they mean, the specialists can interpret them for you.