False-positive Urine Pregnancy Test Due to Leukocyte Interference

Evaluation of Leukocyte and Bacterial Interference in Point-of-Care Human Chorionic Gonadotropin Tests

“…The explanation for the different results observed in the study by Jao et al [1] and the current study are unclear. Jao et al [1] do not describe the source of their WBC preparation, it is unknown if it is from one patient or multiple patients, and the WBC differential is also unknown.…”

“…We observed that most of our false positive specimens were in patients with evidence of urinary tract infection (UTI) and pyuria; with this information, and in the context of the findings by Jao et al [1] that WBCs may result in false positive hCG assays, we evaluated the effect of WBCs or bacteria in urine on the analytical performance characteristics of both devices.…”

“…We read with interest the Letter to the Editor by Jao et al [1] which reported false positive results using the point-of-care (POC) One Step Pregnancy Test device (ACON Laboratories Inc., San Diego, CA, USA). The authors determined that false positive results occurred when the concentration of white blood cells (WBCs) in a urine specimen exceeded 0.4×10 9 cells/L.…”

“…WBCs were prepared on two separate occasions and the total WBC counts of the pools were 57.5×10 9 /L and 200×10 9 /L. These WBC preparations were then diluted into urine from a male patient at six different WBC concentrations (0.1×10 9 , 0.4×10 9 , 1.0×10 9 , 5.0×10 9 , 10.0×10 9 , and 21.0×10 9 /L) including and exceeding the concentration used by Jao et al [1]. The urine was then tested on both the hCG One Step and the hCG Combo Rapid test according to the manufactures' recommendations.…”

“…Jao et al [1] do not describe the source of their WBC preparation, it is unknown if it is from one patient or multiple patients, and the WBC differential is also unknown. It is possible that differences in these parameters could explain the discrepancy.…”