[Blood group expert evaluation: relation between the extent of testing and the reliability of paternity determination. Reflections on revision and guidelines].

In affiliation cases a combined exclusion chance for non-fathers of 99.995% is obtained by the examination of well-established blood group systems. In complicated cases, i.e. if known putative fathers are unavailable, the biostatistical limits for the ascertainment of paternity are obviously very high. They have to be determined by court in each particular case. For routine cases the application of an extended basic blood group expertise, including 19 systems with an combined exclusion chance of 95.17% is considered to be sufficient. The analysis of 263 own filiation cases from 1979 to 1982 yielded an average realistic prior probability of paternity of 83.3%, in 52 many-man affairs even of 90.3%. A similar percentage (89.5%) was observed in 67 two-man affairs of contested legitimacy. Since the father is rarely found among men included at a later stage the rate of children without known father is estimated at 5-15%.