Experience reveals that in most cases genetic tests only make sense if there are certain preliminary indications for a genetic disorder. This may be symptoms for a disease diagnosed in the patient, the genetic test serving as evidence (diagnostic genetic tests).
Another reason for carrying out a genetic test may be a cumulative occurrence of hereditary diseases in relatives. If the disease has a genetic cause or if specific gene variations increase the risk, a genetic test could identify an increased risk. If for instance an increased cancer disposition is established, the person concerned can undergo preventive check-ups more frequently or change his/her way of life. If a recessive genetic disorder occurs in a family, the risk for the offspring can be calculated in the course of a genetic family counselling.

If a genetic test reveals a high risk for acquiring a specific disease this can bring about severe emotional stress. For this reason, a thorough consultation prior to and after a test is required.
A controversial issue is the proof of diseases for which no cure has been found yet. If for example the genetic disorder responsible for the nervous disease Chorea Huntington is identified, the person concerned will know that the disease will occur in the course of his/her lifetime (with Chorea Huntington this can be forecasted with 100% certainty). This can bring about severe psychological problems. On the other hand, a test may also reveal that no genetic variation is prevalent so that the person examined will never acquire the disease.
A further issue lies in the area of data privacy. Genetic information can tell a lot about a person and his/her blood relatives. The abuse of such data can have disastrous effects for those concerned.

If a counselling session has revealed that a genetic test is to be carried out, in most cases a blood sample will be taken. For some tests, cells of the oral mucosa (swab from the mucous membrane) will be sufficient. When the results are available, the person examined will be informed in a further counselling session. If applicable, the next steps will be discussed.

Currently, thousands of different predictive genetic tests are available. However, in most cases only probabilities can be predicted. For instance, it can be observed that one or more genetic variations are prevalent which differ from the "genetic standard" and thus can be attributed to an increased risk of acquiring the disease in question. Since in most cases a multitude of genes interact, with environmental factors also playing a role, most often it is impossible to make any precise predictions. Only in very few cases, e.g. with Chorea Huntington, the occurrence of a disease can be predicted with 100% certainty. However, for this disease, too, the time of the outbreak is rather uncertain.

As a matter of principle, the results of genetic tests are confidential medical data. Their circulation and use is governed by national data privacy acts and regulations.
In Germany, the Gene Diagnostics Law lays down rules both for medical aspects and the fields of work and insurances. The focal point is the individuals' right to informational selfdetermination, i.e. everyone has got the right to acknowledge / ignore such information.
As a principle, employers are prohibited to demand genetic tests from their employees. They must also refrain from demanding, accepting or using the results of any previous tests. When concluding an insurance contract, insurance companies must neither request carrying out genetic tests nor enquire about the results of genetic tests previously carried out. An exception to this is life insurances covering an insurance sum exceeding 300.000 EUR. In such cases, the results of any genetic tests carried out at an earlier time must be made available to the insurance agency.