Accuracy of Whole-Blood Testing for Rapid Detection of Pregnancy

Background and Significance:

Point-of-Care testing to rapidly detect pregnancy in women of reproductive age is common practice in Emergency Medicine departments. The patient history may not always reliably identify the possibility of pregnancy1, and a large proportion of these patients are exposed to potential teratogens because of their emergency department visit. In one study, 33% of such patients received a radiographic evaluation and 75% were prescribed a medication2. Additionally, a pregnancy test is required as the first step in the evaluation of a suspected, potentially life threatening, ectopic pregnancy3.

Commercially available rapid immunochemical assays detect human chorionic gonadotropin (hCG) concentrations >25 mlU/ml, and yield results at 3 minutes using urine and at 5 minutes using serum4-6. However, in clinical practice these tests may take much longer to perform due to significant delays in obtaining urine specimens from patients, or time delays required for separating serum from whole blood. By prolonging patient waiting time for further diagnostic testing and treatment, these delays may adversely impact on patient outcomes, emergency department crowding, and patient satisfaction.

Using whole blood for hCG immunoassay, instead of urine or serum, would facilitate much more rapid emergency department identification of pregnant patients. Whole blood can be obtained immediately during intravenous insertion of phlebotomy, or by finger stick puncture using a lancet in a manner similar to obtaining blood for bedside glucose determination.

Previous study of hCG immunoassays (which were less rapid than the immunoassays which are now commercially available and in use today) utilized whole blood as well as urine and serum, with equal sensitivities7. However, the accuracy of whole blood identifying pregnancy using presently available rapid immunochemical hCG test kits has not been validated.