Home-Based Pregnancy Tests: Study Of Sensitivity

Pregnancy tests done at home are one of the most commonly utilized lab tests by lay persons. These are convenient, easy to use and easy to acquire. However, literature suggests that there is no international standardization of these devices, this makes devices made abroad questionable regarding results. These devices use human chorionic gonadotropin (hCG), which is hormone released by the trophoblast cells. This study used hCG standards to determine the sensitivity of these tests in diagnosing pregnancy.

This study compared the claims made by the package inserts of the tests regarding sensitivity against the test itself. Eight devices from different parts of the world were selected to use against three hCG standards. A technician performed the test, and another read the test after it was photographed. Volunteers also read the tests and their results were compared to those of the technicians. The readings were then compared to the manufacturers package inserts regarding sensitivity. A questionnaire was also administered to the volunteers regarding the testing device. Package inserts were used to determine an expected reading for each device, these were compared against the technician’s reading for which 3 tests agreed with over 90%, 4 agreed with about 80% and 2 tests agreed with less than 50% (Johnson, Cushion, & Bond, 2015). Human chorionic gonadotropin was identified early on as a diagnostic marker for pregnancy (Johnson et al. , 2015).

Due to its sudden and progressive elevation dring pregnancy and lack thereof in a non pregnant state, it is considered a good marker for the diagnosis of pregnancy. At home pregnancy tests are widely utilised, however, due to the inherent heterogenity of the hCG molecuke raises concern regarding what part or type of the hCG molecule they are targeting. The lack of standardization of these tests also hurts the credibility of their results. “Many factors contribute to the erroneous reporting of hCG results, including (a) the complexity of hCG molecule and confusion of nomenclature on the various forms of hCG; (b) laboratory personnel’s lack of awareness of the distinctions of the forms of hCG and failure to recognize the specificity of assays for their measurement; (c) lack of clarity and uniformity in manufacturers’ reagent labeling; and (d) most product inserts’ lack of information on the specificity of each method to the various forms of hCG. ” (Cao & Rej, 2008). “The aim of this study was to evaluate the accuracy of a selection of home-based pregnancy tests relative to the accuracy claims stated on their packaging/product inserts. ” (Johnson, Cushion, & Bond, 2015). In the USA and Europe there are rigorous standards and a certain sensitivity needs to be achieved by tests on the market before the public can purchase them. This does not apply to the rest of the world and it seems that manufacturers are taking advantage of consumers abroad due to the lack of standardization of the hCG assay. “There are [more than] 100 different commercial immunoassay test kits for measuring hCG.

Most procedures detect intact hCG (nicked nonnicked hCG) or hCG hCG, and a few immunoassays detect free hCG alone or with other forms. In clinical laboratories in the US, fewer than 20 immunoassay methods are commonly used. These assays vary in immunospecificity toward different forms of hCG, and results of measurements may have distinct clinical applications. It is important that laboratorians, who perform the test and consult with physicians about test procedures and results, be aware of the heterogeneity of hCG and the specificity of the method in service. ” (Cao & Rej, 2008). Due to the high number of variables the authors of this article hypothesized that majority of these tests were not as accurate as they claimed to be. They also felt that manufactureres of these tests were exploiting lay persosn understanding of the terms ‘accuracy’ and ‘sensitivity’ (Johnson, Cushion, & Bond, 2015). At home pregnancy tests employ an immunometric assay using antibodies that bid to hCG to produce a change in color (Johnson et al. , 2015). Tests from various countries were selected; the authors of this study did not clarify their inclusion creteria for these tests.

The concentrations of these standards had been previously confirmed by quantitative analysis using an AutoDELFIA system, calibrated against the fourth international standard for hCG” (Johnson, Cushion, & Bond, 2015). The tests’ clinical sensitivity was tested and expected results were formed. All tests were expected to yield a negative result with the hCG standard at 0mIU/ml, “all products would be expected to give a high proportion of positive results at 25 mIU/mL, any product with a sensitivity of < 15 mIU/mL would be expected to give positive results at 15 mIU/mL”(Johnson et al. , 2015). These cutoffs were determined based on the manufacturer’s claims of sensitivity. Four out of the eight tests claimed to have a sensitivity to 25mIU/ml, one to 20, one to 12. 5 and another to 10 (Johnson, Cushion, & Bond, 2015). Although the paper emphasizes on the sensitivity of the test, truly the only aspect possible to gauge is the clinical sensitivity. This is because the tests are qualitative and not quantitative, thus only of two diagnosis is possible -pregnant or not pregnant. “Assay standardization requires not only standards but also reference methods (1). The reference method should preferably be a definitive method, e. g. , isotope dilution mass spectrometry. To date, however, neither mass spectrometric nor any other reference method is available for hCG or for any other glycoprotein hormone. In the absence of a definitive method, the best method available can be defined as the reference method. ” (Gronowski, 2009). Ultimately, there is no clear cut answer as to how to measure hCG, whether it should be measured in its totality or various subunits is still up for discussion. “Many home pregnancy tests claim to be more than 99% accurate [26], when used from the day of the expected period. However, these accuracy figures are determined on the basis of laboratory testing of urine samples carried out by trained laboratory technicians under ideal conditions.

The real life accuracy of home-use pregnancy tests may be lower. A review of published studies found that the sensitivity of home-use pregnancy tests declined when subjects performed the test on their own urine compared with the testing of samples done in a laboratory setting” (Gnoth & Johnson, 2014). Two technician were supplied with information in the package inserts of each test and one performed the test while the test was read by another technician who viewed photographs of the results that were taken at read time. These result photographs were then given to a panel of 3 volunteers who were lay users to read and then fill out a questionnaire regarding each device. Each device was tested 24 times using the three standards mentioned previously. At the end of the study the technician that initially read the results, read them again. (Johnson, Cushion, & Bond, 2015). Volunteers for the study were recruited via newspaper advertising and an unspecified database of volunteers. Women between ages 18-45 years were selected due to this being the target demographic for these tests. An inclusion criteria that lacked clarification was that the selected volunteers had not used a pregnancy test within the last three months (Johnson, Cushion, & Bond, 2015).

For the 25 mlU/mL standard the percentage agreement between technician-read result and expected result increased from 45. 8% to 87. 5% for Femitest Jet Ultra, from 83. 3% to 95. 8% for Predictor Early, from 87. 5% to 91. 7% for Haus and from 87. 5% to 100% for David. ” (Johnson, Cushion, & Bond, 2015). The same technician read the results at the first read time and then again after the study, a significant disparity is already apparent. This issue is further exacerbated by the results of the volunteers in comparison to the expected results. “Overall the percentage agreement between volunteer result and expected result was > 95% for Clearblue DIGITAL and Clearblue PLUS; agreement for all other tests was < 75%. The lowest agreement was seen with Cyclotest Early (33. 0%) and Femitest Jet Ultra (39. 4%). ” (Johnson, Cushion, & Bond, 2015). The study also discovered that when the volunteers read the 25mIU/mL standard that only the Clearblue ® PLUS and Clearblue ® DIGITAL were more than 90% in alignment with the expected results.

The other devices ranged from 104% to 48. 6% (Johnson, Cushion, & Bond, 2015). The Cyclotest ® Early yielded a negative result regardless of hCG concentration. Results of volunteer questionnaires regarding use of the products and product preferenceIn the questionnaire administered after the study to the volunteers, Clearblue ® DIGITAL scored well across the board. However, “More than 40% of volunteers scored Cyclotest Early as 1 or 2 for trust and result accuracy, even though the agreement between volunteers reading of this test and expected result with the 15 and 25 mIU/mL hCG standards was < 2%” (Johnson, Cushion, & Bond, 2015). In the free text area of the post study questionnaire, some issues of note were that the volunteers preferred tests with a large window with a clear white background, they found tests with faint lines, patterned backgrounds and color bleeds difficult to read (Johnson, Cushion, & Bond, 2015). This could be of note to manufacturers in streamlining this process. Overall the study was done well with a few drawbacks. Inability to diagnose pregnancy correctly has the potential to complicate pregnancies and issue further testing. Due to the home pregnancy test’s immense popularity the manufacturers there needs to be more standardization.

The WHO established reagents for hCG that have been primarily used in studies like these, however, it is difficult to say whether manufacturers used the same reagents. When reviewing the literature regarding these reagents the suggestion that the WHO standardized“…reference reagents will enable manufacturers to characterize what their “hCG” methods are measuring and to compare the relative recognition of different hCG related materials in different methods. The next generation of assays is likely to be calibrated in terms of the new Reference Reagents” (Bristow, Berger, Bidart, & Birken, 2004). The study also speculates that one of the reasons such a disparity exists maybe because of the form of hCG that is measured. “The reference assay used to confirm concentration does not recognize free β subunit, nicked free β subunit or β core fragment; however, the hCG preparation used does contain these forms, thus an alternative reference assay with broader species recognition would be likely to assign a higher concentration. ” (Johnson, Cushion, & Bond, 2015). The authors doubted their own reference assay, which was a significant discrepancy in the study. “A high number of leukocytes in urine and serum have also been described as the source of positive interference in both qualitative and quantitative hCG assays, respectively. ” (Nwabuobi, Arlier, & Schatz, 2017).

The study also did not specify whether free subunits of hCG were measures by these test or just hCG in itself. One of the biggest limitations of this study was that it was conducted by Clear Blue and the technicians involved were employed by the company. Another limitation the study mentions is that their volunteers were in the UK, where their target demographic had prior experience reading home pregnancy tests. The study emphasizes that these kits are from various parts of the world and that in order to be sold in the USA or Europe significant evidence is required with a sensitivity of 95% or more. The author’s suggestion is thus, “Consistent regulatory standards describing performance requirements for all home-based pregnancy tests are urgently needed. ” (Johnson, Cushion, & Bond, 2015).