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Are expired pregnancy tests accurate? Really? - (10/9/2018)

By Dr. Ron Gasbarro 

Cindy came into the pharmacy and showed the pharmacist a pregnancy test that she has had for several years. “Look, the expiration date was only last month. Is it still OK to use? It’s made of plastic, so I thought it would be still good.” Even though a pregnancy test costs a few bucks, many people do not have that money to pay. 

The pharmacist explained to Cindy how a pregnancy test functions. Home pregnancy test strips work by detecting the pregnancy hormone human chorionic gonadotropin (HCG) in the woman’s urine. The further along you are in the pregnancy, the higher the level of HCG. Most commercially available pregnancy tests are advertising as being 99% accurate. But what if the pregnancy test is expired? Should you rely on the result of the expired pregnancy test? You may as well flip a coin. 

The test strip contains a chemical that reacts with HCG. After the test has expired, this chemical is likely ineffective at detecting this pregnancy hormone in the urine. Manufacturers assign each test an expiration date based on the effectiveness of that chemical. Most commercially available pregnancy tests have a shelf life of between 2 and 3 years after manufacture. This is clearly marked on the box. A test that expired for months or even years ago will undoubtedly give a false reading, called a false negative. This is because the chemical needed to react with the HCG is not potent enough to detect the hormone. No one wants to find out 10 or 15 weeks down the road that one is actually pregnant, interfering with plans, employment, and finances. 

Despite the manufacturers’ claims that pregnancy tests are 99% effective, this is only true if they are used properly. For instance, the woman may be taking the test too early. There may not be enough HCG in her urine for the test strip to detect it. About 3% of pregnant women may still show a false negative after the first missed period because their levels of HCG are not high enough. Due to the rapidly increasing levels of HCG in a pregnant woman, a negative result about one week after a missed period is typical. These women should repeat the test after a few days to allow the HCG levels to increase. 

Also, the test may not be done according to the instructions. Read the package insert carefully to ensure that the test is used correctly. If you are the user, test with the first passing of urine in the morning after awakening when the HCG concentration will be the highest. Take note of whether the test is a midstream test or whether the stick is dipped into the urine. Most tests require 3 minutes to produce a result. Reading the results on some tests should be done within 10 minutes otherwise the result is invalid.

What about, as in Cindy’s case, if the test expired just a few weeks before? If for example, the test expired in early September, then it should be accurate in late October. However, if the test came up negative and you suspect you are pregnant, then yes, crack open your piggy bank and buy a new one.

Cindy really needed to find out if she is pregnant because of her job and her family. So, she decided to purchase a new test and go from there based on the actual results.

Ron Gasbarro, PharmD, is a registered pharmacist, medical writer, and principal at Rx-Press.com. Read more at www.rx-press.com  

 


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