The heterozygote test is performed on a clinically healthy person. It is not a predictive diagnostic tool in the narrow sense of the term, since in this case merely an invariable genetic status of a healthy person is established no predictive information is collected. The test is used for the early detection of recessive hereditary diseases, thereby making it possible to determine for couples that are healthy but related to ill persons whether possible genetic defects can be passed on to a child in the future. The goal is to estimate as far as possible the likelihood that future descendants could become ill. Testing for heterozygosity is performed for the most part with respect to early onset, severe and incurable diseases such as Duchenne muscular dystrophy, cystic fibrosis or spinal muscular atrophy.

A special instance of a heterozygote test is the screening programme performed on Cyprus. In a screening programme the conduct of the test is not restricted to a single individual; instead, an entire group of people is tested. The purpose of a screening programme can, for example, be to prevent or curtail genetic hereditary diseases. Cyprus is a country with a high prevalence of the inheritable blood disease beta-thalassaemia major. Every seventh inhabitant of Cyprus is a carrier of the defective genetic information without themselves becoming ill. If left untreated the course of the hereditary disease is fatal. Only by administering expensive drugs is it possible to enable a diseased individual to survive into adulthood. Since 25 % of children whose father and mother are carriers of the defective gene become ill, new cases arise every year. Without outside intervention the number of individuals to fall ill with the disorder would have doubled roughly every eight to ten years. For this reason, the following measures were adopted in Cyprus: With the aim of prevention, Cyprus first conducted a screening programme in 1973 to identify carriers of beta thalassaemia. Since 1977 screening concentrated on prenatal diagnosis. As a result, many pregnancies in which embryos had been tested positive for beta thalassaemia were terminated and the prevalence of beta thalassaemia fell sharply. This reduction was reinforced a call from the Greek Orthodox Church to provide a proof of participation in a screening and counseling by the National Thalassaemia Centre before the church wedding. Gradually, information about screening programmes and the possibility of prenatal diagnostics was also integrated into civil marriage procedures.