title: Implication of negative urine pregnancy testing in subjects with unknown last menstrual period.
abstract: BACKGROUND
  In laboratory medicine, a urine pregnancy test is an easily available diagnostic test today. Urine pregnancy is a monitoring of human chorionic gonadotropin (hCG), which is secreted by the trophoblastic cells of the placenta. The most common indication for a urine pregnancy test is secondary amenorrhea. However, there are other conditions that can lead to secondary amenorrhea. Only a few recent studies have estimated population pregnancy rates using objective, laboratory-based criteria.
  
  
  METHODS
  A study on laboratory-measured pregnancy rates and the correlation to age in a tertiary hospital in Thailand was carried out. This study not only provides good information from a medical aspect but also from a social aspect. The data from the medical records of female patients who underwent a diagnostic urine pregnancy test at the Division of Laboratory Medicine, King Chulalongkorn Memorial Hospital, Bangkok Thailand from August 2004 to December 2004 were reviewed. The definitive last menstrual period was not known for all subjects.
  
  
  RESULTS
  There were 1,005 medical records reviewed in this study. From the total medical records, there was no subject younger than ten years or older than 50 years of age. The diagnostic test results were positive in 121 cases (12.0%) and negative in 884 cases (88.0%). Classified by age group, we found that most subjects were under 35 years of age. The laboratory-measured pregnancy rates in the subjects aged less or equal to, or more than 35 years old were 11.3% and 14.8%, respectively. There was no significant difference in positive rate in either group.
  
  
  CONCLUSIONS
  In our setting, a negative pregnancy test in the presence of amenorrhea can imply more than a pregnancy. Close follow-up and checking for other possible pathological conditions should be considered.
authors.affiliation: Department of Laboratory Medicine, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand.
authors.forename: V
authors.initials: V
authors.lastname: Wiwanitkit
mesh_terms: D000293:Adolescent; D000328:Adult; D000568:Amenorrhea / Q000453:epidemiology / Q000209:etiology*; D002648:Child; D005260:Female; D006801:Humans; D008875:Middle Aged; D011247:Pregnancy / Q000652:urine*; D018873:Pregnancy Rate; D011258:Pregnancy Tests / Q000379:methods; D013785:Thailand / Q000453:epidemiology