Normal values and reference range

What normal values and reference range mean

In order to detect diseases or monitor their progress, the physician can have measured values determined in the blood or other body fluids or in tissue samples in the laboratory. As a guide as to which values could be conspicuous, the laboratory gives normal values or reference ranges. The words “normal values,” “standard values” and “reference range” basically mean the same thing. If you measure a certain laboratory value in healthy people, this value is rarely exactly the same in other healthy people and also in the same person at different times. All values are subject to natural fluctuation and can be considered “normal”. They lie within a certain range, this is called reference, normal or normal range. This range is determined for a particular laboratory value by measuring the value in a very large number of healthy people. The range in which 95 percent of the values then lie is the reference range. This means that 5 percent of healthy people have a higher or a lower measured value. Therefore, one should speak of reference values rather than normal or standard values.

If a laboratory value exceeds or falls below the limits of the reference range, the measurement should be repeated (several times) to avoid misinterpretation. If the deviation is confirmed, careful monitoring of the value is usually advisable.

Laboratory values alone do not allow a diagnosis

As mentioned above, people with a laboratory value outside the normal range may nevertheless be healthy. Conversely, a person with a value within the normal range may well be ill. A laboratory value determination alone is therefore not sufficient to determine whether someone is healthy or ill. It is also necessary to ask the patient about his or her medical history (anamnesis), to perform a physical examination and sometimes to use other examination methods. Only all findings together allow a diagnosis.

Old units and SI units

For centuries, very different standard systems were used in medicine, based on different measurement systems. This often caused confusion because of different units. For this reason, an internationally valid system, the Système International d’Unité (SI for short), was agreed upon in 1971. The SI units now only include the parameters meter (m), kilogram (kg), second (s) and amount of substance (mol).

In Germany, the SI system has so far been used mainly in scientific articles. In everyday hospital routine or in practice, many professionals still use the old units. For example, laboratories often report the hemoglobin value in the “old” unit g/dl, not in the SI unit mmol/l.

Examples of units