tesco pregnancy test sensitivity
Positive Pregnancy Test Tesco - pregnancy testWhat else does a profession have to do to deserve an adequate salary increase?' STEVE FORD, EDITOREvaluation of home pregnancy test kits for reliability 03 July, 2007 By VOL: 103, ISSUE: 27, PAGE NO: 30-31 Michael J Wheeler is a clinical scientific consultant; Susan Lamph is an evaluator; Stephen Halloran is a clinical scientific consultant; all in Guildford Medical Device Evaluation Centre, Postgraduate Medical School, Guildford, Surrey. Michael J Wheeler, PhD, MSc, BSc, FRC Path; ; Susan Lamph, AIBMS; Stephen Halloran, MSc, BSc, DipCB, FRC PathPregnancy kits for home use are used widely in the UK and the Purchasing and Supplies Agency of the Department of Health commissioned an evaluation of all the products available. This study has identified 30 different kits, 27 of which have been evaluated. All devices were able to give a positive result for pregnancy at the time of the first lost period. Areas of confusion and possible errors have been identified. Previous studies have shown that although a device is reliable a high proportion of women reported an incorrect result due to the incorrect use of the device. It is therefore important that women who are presented to the clinic with the result of a pregnancy kit at home have the result confirmed by a trained professional. Contraceptive pregnancy kits have been made available in the United Kingdom since the late 1970s. Early tests could detect levels of 200-500IU/L human choral choral choral choralin gonadotropin (hCG) so that the tests were delayed better up to two weeks after the last lost period. The sensitivity of 10-50IU/L hCG was made possible with the availability of monoclonal antibodies and refined techniques. HCG is detected in blood and urine after a foetus is implanted in the uterus. Valanis and Perlman (1982) found that 33% of women, testing less than nine days after the last lost period, had false negative results. Bastian et al (1998)reported that most false negative results are due to users not using the kits properly. However, very few studies have been conducted on the reliability of TBT pregnancy testing devices. A recent study in Germany by SiekmeierandLutz(2007) suggests that pregnancy test kits are very reliable. They considered all notifications reported as failures of the Federal Institute for Medical Medicines and Devices in Germany of in vitrodevices (including TBT pregnancy test devices) between 1999 and 2006. There were 207 notifications related to TBT devices of which 25 (12.1%) were pregnancy test devices. Notifications of these devices depend on doctors and users who report failures and this could be a serious underestimation of the true incidence of failures. Products evaluated in 1999 all had levels of sensitivity of 25-50 IU/L hCG (Wheeler, 1999) and used an immunochromatography technique. This is essentially a mecha technique where the applied urine spreads along an absorbent material that reacts with different antibodies along the way. The products evaluated in 2006 reported here use exactly the same technique but have sensitivity of 10-50 IU/L. As the urine advances along the wick any hCG in the urine is combined with a monoclonal antibody (raised in a mouse) to the β subunit of hCG (hCG is made of two subunits, an α- and a β-subunit. The hCG linked continues along the wick to the test reading area where it is 'captured' by another monoclonal antibody aimed at hCG subunit. The β-subunit antibody continues along the wick to the control area where it is captured by an anti-mouse G immunogloulin antibody. Devices are a flat plastic case or a palette in which some urine drops are added to the sample well (dipstick/pallet), or a stick design that can be placed either in the urine flow or in a collected urine glass (middle current dipstick). The latter is the simplest device. Those that can be placed in the urine flow have a plastic shell with a small amount of fuse exposed at one end to place in the urine flow. A plastic cap is provided to cover the absorbing tip after use. ObjectiveThis evaluation was carried out for the Test-Based Shopping Centre (CEP) which is part of the Policy and Innovation Directorate of the NHS Purchase and Supply Agency. The study was commissioned by CEP to assess the reliability of OTC pregnancy testing devices available in the UK. 30 different OTC pregnancy test kits were identified available in pharmacies, supermarkets or Internet. Evaluation method Companies were informed that an evaluation of TBT pregnancy tests was being conducted. They were sent the test protocol and invited to submit their products for evaluation. Of 20 companies, 15 agreed to evaluate their devices. Chefaro Ltd was redesigning its device (Predictor), while Boots, LPC Medical (UK) (Easistix P), Home Health UK (Fastest) and Lloyds decided not to send their devices for evaluation. The previous versions of Boots, Chefaro Ltd and Lloyds products evaluated by Wheeler (1999) were all reliable and convenient to use, however these are not currently available products. All tests were performed in a well-lit laboratory and two operators confirmed the results. The lowest HCG concentration detected by each kit was examined in two ways: All devices were tested with both sets of sample dilutions to determine sensitivity. The results were recorded as negative, positive, weakly positive and very weakly positive. Since the very weakly positive results were only unvisable, they were considered to be easily lost in a less well-lit environment with a single operator. No details are available on how each manufacturer determines the sensitivity of its kits so it was decided that the detection limitation (sensitivity) of each kit was the concentration in which more than 50% of the results of the previous specimens were at least weak positive. This provided a standard approach to sensitivity testing for all kits. urine samples of six menopausal women were also tested. HCG concentration in women of reproductive age who are not pregnant is ResultsFull details of the 2006 evaluation can be found, including tested kits and individual results obtained in Lamph et al (2006a, 2006b). Table 1 lists the manufacturers, the devices they supply and the type of device. The kits arrived in three formats: dipstick, dipstick of medium current and palette. Dipstick devices are only suitable for placing in a collected urine glass, medium-current dipsticks can be placed in a urine flow or in a collected urine vessel, while a pallet device requires the collection of a urine specimen before putting a few drops of the urine on the test device. A group of women were asked to state their preference for each type of device. The preferred device was the average current dipstick, as it did not require any urine collection if placed in the middle and was very simple to use. User Views Users found less intuitive pallet devices to use and some had difficulties using droppers to add the correct number of drops to the sample well. Although the dipstick device was easier to use, users were worried about the use of the device too far in the urine and found reading results more difficult than when using the pallets or dipstick medium-current devices. These devices also required the urine to be collected first. Users thought it useful for a collection container to be supplied with pallet and dipstick devices. The collection devices are supplied with the EARLY BIRD, RapidselfTest, Reveal, TRUELINE and Unitest, but are of variable quality. Some users found the collection vessels supplied with the RapidselfTest and Reveal kits too little deep and none of the users liked the folding container supplied with the single pregnancy cassette test. Although the average current dipsticks were easier and more convenient to use, some users found that with some tests the excess of dripped urine from the absorbent tip before the tip cover could be replaced and this was perceived to be messy. Accuclear's compact pregnancy test and Mediplystream's mid-age pregnancy test were the only devices to avoid this problem. Leave the dipstick in the urine flow for 10 seconds as recommended with the ASDA home pregnancy test, QUIK-CHECK midstream and TESCO home pregnancy test felt too long by some users. The reading results were not a problem, although some users found the vertical negative line in the pregnancy test Clearblue confusa and would have preferred a clear window for a negative result. Sensitivity The sensitivity reported for devices ranges from 10 to 50IU/L hCG. This evaluation was in accordance with the stated sensitivity of manufacturers in 14 cases. It was found that a device was more sensitive and the rest less sensitive, usually by a dilution factor. The TRUELINE pregnancy test was two less sensitive dilutions than those cited when read in three minutes, but was more sensitive when read in 10 minutes. The results of the sensibility tests are given in Table 2. The differences between the evaluation result and the data cited by the manufacturers may be due to several reasons: Three QUIK-CHECK devices had a claimed sensitivity of 10IU/L. It is possible that in this sensitivity some urine samples of women who pass through menopause may have tested positively. For such urine samples, the EARLY BIRD gave two positive results: one weak the other very weak positive. Negative results were obtained with all other devices. In the examination for a hook effect eight devices had a weak positive result at 500.000IU/L hCG but a clear positive test at ≤100,000IU/L. The devices that show this effect were Accuclear, ASDA, Mediply midstream, both QUIK-CHECK, Reveal, TESCO and TRUELINE. Thus, higher concentrations of hCG would give an even weaker result. The TRUELINE device can be read from three minutes to 10 minutes. In the shortest recommended reading time a sensitivity of 100IU/LHCG was found compared to the reported sensitivity of 25IU/L. When the device was read using the longest recommended reading time, a 50IU/L sensitivity was found. Discussion When the TBT pregnancy test kits were last evaluated in the UK for the MHRA (Wheeler, 1999) there were only nine different devices. There are now 30 different devices available, including the brands of supermarkets, as well as additional company devices. Therefore, the choice is wider and potentially even more confusing to users than ever before. This evaluation examined the sensitivity, reliability and ease of use of 27 different pregnancy test devices from 15 companies. Five companies rejected the offer to include their devices in the evaluation. The reasons were not declared except for Chefaro Ltd, who was redesigning his Predictor device. There are reports, many anecdotes, that false positive and false negative results are occasionally obtained with pregnancy test devices. Studies that examine this problem have shown that in many cases it is due to the user who does not perform the tests correctly (Bastian et al., 1998). Daviaud et al(1993) sent 478 positive urine samples to 638 lay people for testing. False negative results were obtained for 230 of these specimens. Valanis and Perlman (1982) also reported high error rates and Doshi (1986) drew attention to the false positive results that were also obtained. For every 10 urine samples that do not contain HCG were reported positive. It is important that the instructions be clear, easy to read and come with clear diagrams. Wheeler (1999) noted that some instructions had a very small impression, while others had instructions that ran over two sides of an instruction sheet so that the full instructions could be lost. In this evaluation the instructions were easy to follow for everyone except Unitest devices. Unitest instruction leaflets had a small impression that was difficult to read and basic instructions were included in the aluminium test wrap. The sample application volume required for the pallet device differs between the foil wrap and the printed instructions. In addition to false results due to users who do not follow or understand instructions, there are methodological problems that can lead to false results. These include poor sensitivity of the device, hypersensitivity of the device, hook effect, and cross-reaction with LH (Lighting hormone). In the last case all antibodies used on these devices are reported to have very little cross-reaction with LH. It has not been possible to establish how each company determines the sensitivity of its devices. Some may include very weak positives such as their detection limit and may consider the concentration in which only positive evidence is observed or a certain percentage of positive results is observed. In addition, companies use three different international standards to calibrate their test kits. We standardize our sensitivity calculation to provide a direct comparison of devices. It is not surprising that there are differences between our sensibility figure and that reported by a company, but only in one case there was a difference of more than one dilution. This was with the TRUELINE device that could be read from three minutes to 10 minutes. All kits offer a time range on which you can read a result. Some kits showed greater sensitivity in the longer time. It was especially confusing when the kits gave alternative reading times - for example, the instructions indicated that the DISCOVER Today device should be read between one and two minutes, but also stated that the kit should not be read after 10 min. CHECKMATE-EZE suggested that the results could be read up to 15 minutes after the device contacted the urine sample. We record the results as soon as possible and the last recommended times. The sensibility calculated twice did not change for 16 devices, but five devices (ASDA, CHECKMATE-eEZE, Clearblue DIGITAL, EARLY BIRD and TESCO) were more sensitive in the longer time. We are concerned to provide a time window for devices that are used by untrained people. A negative result can occur in shorter reading time but a weak positive in longer reading time. You can imagine that a user is not sure if he is pregnant or not. In addition, we find that the EARLY BIRD and Unitest pallet devices gave irremissible results in the shortest time recommended due to the background color obsessing the test window. We recommend that manufacturers provide a single reading time. It has been reported that hCG concentrations in women going through the menopause can rise to between 5IU/L and 10IU/L (Borkowski and Muquardt, 1979). Three QUIK-CHECK devices have a reported sensitivity of 10IU/L. It is possible that a device with low sensitivity can give a false positive result in women who pass through menopause. This happened with the EARLY BIRD device. The hook effect in immunometric sandwich trials, as used in these devices, causes falsely low results. This is due both to the signal and to the catch antigen swamped antibodies - in this case hCG. Manufacturers have cited HCG concentrations of ±250,000IU/L at 8-10 weeks. Multiple pregnancies and secret HCG tumors can produce even higher HCG concentrations, but this is a rare occurrence. Although most urine samples analyzed for pregnancy are collected shortly after the last lost period, women will occasionally wait several weeks before testing the pregnancy - when the HCG concentrations will be very high. We tested the reliability of the devices up to 500,000 IU/L. Eight devices yielded a weak positive result in this concentration, although a positive strength at 100,000 IU/L. This indicated that these devices suffered some hook effect. In this high concentration all results were considered positive and therefore indicate pregnancy, but the signal would be even weaker or absent at higher concentrations. Conclusion All devices we tested were able to detect pregnancy at the time of the first lost period. Therefore, if a woman reads and follows the instructions carefully, she must achieve a precise outcome at this time. It should be noted, however, that previous studies have determined that a high proportion of women do not achieve the correct outcome. This evaluation has shown some variability between devices and areas, especially with correct reading times, where a woman may be confused by reading a result. The false positive tests for the urine of women who pass through menopause with the EARLY BIRD device are of particular concern. Our users found that not all devices were easy to use and this could lead to mistakes. As such, when a woman presents at the clinic with a result with a home test kit, she should always be tested by a professional operator with pregnancy testing experience. Bastian, L.A. et al (1998) Diagnostic efficiency of home pregnancy test kits. Family Medicine Archives; 7: 5, 465-469.Borkowski, A., Muquardt, C. (1979) Human choraline gonadotropin in the plasma of normal non-pregnant subjects. New EnglandJournal of Medicine; 301: 6, 298-302.Daviaud, J. et al (1993) Reliability and feasibility of domestic pregnancy tests: Laboratory Validation and Diagnostic Assessment by 638 volunteers. Clinical Chemistry; 39: 1, 53-59.Doshi, M.L. (1986) Precision of household consumption for early detection of pregnancy. American Journal of Public Health; 76: 5, 512-514.Lamph, S. et al (2006a) About pregnancy tests. Report 06051. Procurement and Purchasing Agency, NHS, UK. www.pasa.nhs.uk. Lamph, S. et al (2006b) During pregnancy tests: Supplement for technical data. Report 06051-S. Procurement and Purchasing Agency, NHS, UK. www.pasa.nhs.uk.National Institute for Biological Standards and Control, UK (2004) Fourth International Standard for Chorionic Gonadotrophins. NIBSC75/589 National Institute for Biological Standards and Control www.nibsc.ac.uk/documents/ifu/75-589.pdfSiekmeier, R., Lutz, J. (2007) Experience with post-market surveillance of in-vitro diagnostic medical devices for use in Germany. Clinical Chemistry and Laboratory Medicine; 45: 3, 396-401.Valanis, B., Perlman, C.S. (1982) Pregnancy Test Kits in the Home: Prevalence of use, phony-native rates and compliance with instructions. American Journal of Public Health; 72: 9, 1034-1036. Wheeler, M.J. (1999) Start and pregnancy test lab. Professional nurse 14: 8, 571-576. or a new account to join the discussion. Posts Claire Grant's nursing career has taken her all over the world, with spells... 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