We have previously blogged about false negative urine qualitative hCG tests in both point-of-care (POC) hospital devices and over-the-counter (OTC) devices due to the presence of high concentrations of hCG beta core fragment (hCGβcf ). This is a problem because after approximately 7 weeks of pregnancy many women have concentrations of hCGβcf much higher than intact hCG. Furthermore, it is impossible to predict which women are likely to produce urine with high hCGβcf concentrations and at what point in pregnancy the increased concentrations will be encountered.
In 2014, our group published a screening method to determine which pregnancy devices were effected by high concentrations of hCGβcf. In that study, we reported that the OSOM (Sekisui Diagnostics) POC device was one of two of the most susceptible to false-negative results. Recently, we became aware that there are three OSOM hCG POC devices available commercially: OSOM Card, OSOM Ultra hCG, and the original OSOM Combo. We were hopeful that the manufacturer had improved their devices, as other manufacturer have done, and we have blogged about. We utilized the same screening method we have previously reported and tested all three devices, compared to the Beckman Icon 20.
We were happy to find that the OSOM Ultra had improved performance and was not effected by concentrations of up to 50,000 pmol/L hCGβcf. However, the OSOM Card had the same performance as the original OSOM Combo device. It is disturbing that these two devices are still marketed for use and they do not warn the user of the potential for false negative results.
The package inserts of the OSOM Combo and OSOM Card devices state:
“This assay is capable of detecting only whole molecule (intact) hCG, which is the predominant form of hCG in early pregnancy. It cannot detect the presence of hCG fragments or free subunits. In later term pregnancies (generally beyond the first trimester), occasionally urine samples can contain very high levels of hCG fragments. Therefore, the OSOM Pregnancy test is most effective when used for the detection of pregnancy in earlier stages.”
However, as stated above, concentrations of hCGβcf are known to be increased as early as week 7 of pregnancy.
Users need to be aware that these types of devices are still marketed. Read the package insert carefully. Phrases such as “This assay is capable of detecting only whole molecule (intact) hCG” and “It cannot detect the presence of hCG fragments or free subunits.” Suggest that the device may give false negative results of concentrations of hCGβcf are high. If your urine pregnancy test is negative and you suspect you may be pregnant, we suggest you have a serum hCG test performed.