ABSTRACT
Most urine tests used today to detect pregnancy are immunochemical tests which detect Human Chorionic Gonadotropin (HCG). Elevated HCG levels in urine were formerly detected by biological assay of this hormone. Immunochemical tests depend on antigen-antibody reactions. They provide results in a much shorter time than biological tests. Immunochemical reactions occur in minutes or hours, whereas many biological assays require days. Immunochemical methods for testing for pregnancy are classified as either tube tests or slide tests. The limitations of pregnancy testing include the fact that none of the tests is 100% perfect. This is true with any laboratory test, but 100% accuracy appears to be one of the special characteristics expected of pregnancy tests. There are a significant number of specimens in any series which give results more difficult to read than others. Because of this variability, and especially with inexperienced personnel, it is good practice to run both positive and negative controls.
