"Hook-like effect" causes false-negative point-of-care urine pregnancy testing in emergency patients.

BACKGROUND: Failure to detect pregnancy in the emergency department (ED) can have important consequences. Urine human chorionic gonadotropin (uhCG) point-of-care (POC) assays are valued for rapidly detecting early pregnancy with high sensitivity. However, under certain conditions, POC uhCG tests can fail to detect pregnancy. OBJECTIVES: In investigating a series of late first-trimester false-negative pregnancy tests in our ED, a novel and distinct causative phenomenon was recently elucidated in our institution. We discuss uhCG POC tests, review our false-negative rate, and describe mechanisms for false negatives and potential remedies. DISCUSSION: The false-negative POC uhCG rate is very low, but in the setting of a large volume of tests, the numbers are worth consideration. In positive uhCG POC tests, free and fixed antibodies bind hCG to form a "sandwich"; hCG is present in several variant forms that change in their concentrations at different stages of pregnancy. When in excess, intact hCG can saturate the antibodies, preventing sandwich formation (hook effect phenomenon). Some assays may include an antibody that does not recognize certain variants present in later stages of pregnancy. When this variant is in excess, it can bind one antibody avidly and the other not at all, resulting in a false-negative test (hook-like phenomenon). In both situations, dilution is key to an accurate test. CONCLUSIONS: Manufacturers should consider that uhCG tests are routinely used at many stages of pregnancy. Characterizing uhCG variants recognized by their tests and eliminating lot-to-lot variability may help improve uhCG test performance. Clinicians need to be aware of and familiarize themselves with the limitations of the specific type of uhCG POC tests used in their practice, recognizing that under certain circumstances, false-negative tests can occur.

Evidence of endemic goiter and iodine deficiency in a mountainous area of Haiti.

OBJECTIVE: To investigate reports of iodine-deficiency disorder in a specific area of Haiti. METHODS: In March 2008, this cross-sectional study was performed in an area 15 miles northeast of Jacmel, Haiti, within the Chaîne de la Selle Mountains. Before arrival of the study team, an announcement was made throughout local villages soliciting volunteers to meet at a central location. Of those who arrived, participants were selected in an attempt to sample individuals from all age groups, regardless of goiter status. After providing verbal informed consent, each participant was photographed and assigned a number to be used to protect privacy. An examiner performed palpation of the thyroid gland on each participant in accordance with World Health Organization criteria. Results of palpation were classified into 3 grades: grade 0, the thyroid gland was not palpable; grade 1, the thyroid gland was palpable but not visible; and grade 2, the thyroid gland was palpable and visible while the patient was in a normal position. Casual urine samples were collected from each participant and analyzed spectrophotometrically for urinary iodine concentration. RESULTS: Eighty-eight individuals aged 2 to 72 years participated in the study. Median urinary iodine concentration was 39 microg/L. Of the 88 participants, 82 (93%) were iodine deficient (18 [20%] were severely deficient), and 45 (51%) had goiter on physical examination, including 27 with grade 1 goiters and 18 with grade 2 goiters. CONCLUSIONS: We have documented iodine deficiency with associated endemic goiter in this previously uninvestigated Haitian population, for which world health agencies currently lack definitive data. These data have potential implications for both the local area and the country as a whole where further evaluation and treatment are needed for persons at high risk for iodine-deficiency disorder.