"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.

Viscosupplementation: a new treatment option for osteoarthritis.

Osteoarthritis (OA), a degenerative joint disease affecting articular cartilage and synovial joint fluid, is the most common of the rheumatic diseases. OA is a huge public health issue that diminishes the quality of life of millions in the United States. Current treatments for OA include physical therapy, antiinflammatories, narcotics, steroids, and surgery. Unfortunately there is currently no cure for OA and many of the effective treatment modalities have many harsh side effects. Quite recently patients suffering from OA had little alternative to total joint replacement surgery once they exhausted their allotment of steroid injections and started to experience the GI complications associated with traditional NSAIDs. The introduction of viscosupplements, injectable compounds that mimic healthy synovial fluid and often relieve the suffering caused OA, has given patients with OA a longer-term, nonsurgical treatment alternative.