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Home Pregnancy Tests (HPT)

Human chorionic gonadotropin, or hCG for short, is produced by the placenta of the implanting embryo. hCG is  commonly known as  "the pregnancy hormone".  Home pregnancy tests have substances in them that will combine with the HCG in your urine to form a visible  line or plus sign if the level of HCG in your urine is high enough for the test to detect. It usually  takes about 10 days after conception before hCG can be detected by a home pregnancy test in your urine. A few tests are able to find hCG at very low levels in  your urine, and can detect up to 97% of pregnancies on the day of a missed menstrual period.

For all pregnancy tests, follow the directions exactly. Test your urine first thing in the morning, when your urine is most concentrated. The tests usually take about 5 to 10 minutes to detect hCG.
 

Most home pregnancy  tests are performed by dipping the test strip into a sample of your urine or by urinating directly on the test strip. The pregnancy test has a "control band"  to let you know the test has been done correctly. If there has been enough urine absorbed by the test strip and the test is working properly, a line should appear in the control area of the test .

 If no  control band appears at all, you most likely did not apply enough urine to the test strip, and you will need to repeat the test . If the problem occurs again, there may be technical problems with the test, and  you should stop using the test kit and contact your local distributor.

After one to ten minutes  if the amount of  hCG   in your urine is high  enough  to be detected by your test,  a second colored line will appear on the test in addition to the control line .
 

On some  tests, the lines will  overlap to form a plus sign.


All results should be confirmed by your healthcare provider, especially when making decisions about future medical care.


Result: Negative Pregnancy Test

Only a control band appears .
This means the amount of hCG is less than the pregnancy test is able to detect.

 Is it possible the test could be wrong? 

Yes. False negative pregnancy test results can occur. A false negative pregnancy test  is a test result that says you're not pregnant when you really are pregnant. Some possible reasons for a false negative pregnancy test  include:

  • You did not wait long enough for the substances in the test to combine with the hCG in your urine. Repeat the test and wait ten minutes.

  • You took the test too soon. Wait  3 to 7 days and repeat the test.

  • Your urine is too dilute. Drinking too much fluid before taking a home pregnancy test waters down the level of the hCG in your urine making the amount of hCG  too low for some tests to detect. Retest your urine first thing in the morning before you drink any fluids.

  • A very high hCG level (or one of hCG's forms) in your urine is preventing the substances in the test from combining properly. This is known as the hook effect. This is most likely to occur  after 5 weeks of pregnancy. Add water to your urine sample to lower the level of hCG in your urine and retest your urine.

If you have missed a menstrual period and have lower abdominal pain, call your health professional immediately even if the pregnancy test is negative. You could have an ectopic pregnancy (a pregnancy implanted outside of the uterus)  which can be life threatening to you.


Result:  Positive Pregnancy Test

A control band and a second line or a plus sign appears. *
The test has detected the presence of hCG.
Is it possible the test could be wrong? 

Yes. False positive pregnancy test results can occur, but they are much less common than false negative pregnancy tests.  A false positive pregnancy test  is a test result that says you're pregnant  but you really are not pregnant.. Some possible reasons for a false positive pregnancy test include:

  • You have had a pregnancy termination or miscarriage within the last 5 to 6 weeks.

  • You have been taking medications that contain hCG (such as Pregnyl, Profasi, Pergonal, A.P.L.).

  • The test is defective.

  • hCG is being produced by a source other than normal placenta such as:

    • Trophoblastic disease, breast cancer,  lung cancer, tubo-ovarian abscess

    • The pituitary gland in postmenopausal women .

*If a control band and a faint second line or a plus sign appears you could be pregnant. Wait a few days and retest your urine or go to ask to see your health care provider

REFERENCES

1. Cole LA.The utility of six over-the-counter (home) pregnancy tests.Clin Chem Lab Med. 2011 Aug;49(8):1317-22.PMID:21812725
2. Davison CM, et al., Qualitative beta-hCG urine assays may be misleading in the presence of molar pregnancy: a case report. J Emerg Med. 2004 Jul;27(1):43-7. PMID:15219303
3. Gronowski AM, et al., False-negative results in point-of-care qualitative human chorionic gonadotropin (hCG) devices due to excess hCGbeta core fragment. Clin Chem. 2009 Jul;55(7):1389-94. PMID:19395437
4. Grynberg M, et. al., Rupture of ectopic pregnancy with negative serum beta-hCG leading to hemorrhagic shock. Obstet Gynecol. 2009 Feb;113(2 Pt 2):537-9. doi: 10.1097/AOG.0b013e318190a2bb.PMID:19155948
5. Er TK, et. al., False-positive urine pregnancy test in a woman with adenomysosis. Am J Emerg Med. 2009 Oct;27(8):1019.e5-7. doi: 10.1016/j.ajem.2008.12.023. Epub 2009 Sep 22. PMID:19857433
6. Maughan BC, Kamat A.Lung carcinoma presenting with pathologic femur fracture and false-positive pregnancy test result.Ann Emerg Med. 2012 Sep;60(3):378-80. PMID:22424649
7.Levsky ME, Handler JA, Suarez RD, Esrig ET. False-positive urine beta-HCG in a woman with a tubo-ovarian abscess. J Emerg Med. 2001;21:407409.PMID:11728769
8.Cole LA, et. al.,  Accuracy of home pregnancy tests at the time of missed menses. Am J Obstet Gynecol. 2004 Jan;190(1):100-5.PMID:14749643

See also

Beta hcg Calculator

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