VARIOUS CAUSES of false-positive biological pregnancy tests have been reported.1-3 Recently a latex agglutination inhibition test has been developed. This test detects, immunologically, human chorionic gonadotrophin in urine. Urine from a pregnant female contains chorionic gonadotrophins shortly after implantation and reaches a high peak approximately 1 mo after the first missed menstrual period. If a urine specimen containing chorionic gonadotrophins is incubated with a solution containing human chorionic gonadotrophin antibodies, the gonadotrophins are neutralized. If this solution is then incubated with an antigen containing latex particles coated with human chorionic gonadotrophin, agglutination does not occur following centrifugation. The supernate will thus remain turbid and indicate a positive test. If, on the other hand, there is an absence of gonadotrophin in the urine, no neutralization occurs and subsequent incubation with the antigen produces agglutination leaving a clear supernate following centrifugation.
It has been reported that 200 to 300 international units