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Understanding false positives & negatives

  • Pregnant woman
  • Positive Pregnancy result
  • Positive Pregnancy result

Understanding false positives & negatives


There is always some sort anxiety or apprehension when trying to fall pregnant.
You sit at home waiting for the dark line to show up on your pregnancy test, confirming a positive result. 
The waiting itself is tortuous but then you can’t stop thinking about whether the test is accurate.



How do pregnancy tests work?

During your menstrual cycle an egg travels down the fallopian tube to be fertilised by a sperm cell. Once fertilisation takes place the egg is implanted into the uterus and the placenta is formed.

The placenta secretes the human Chorionic Gonadotropin hormone (hCG) which is present in the urine.  The presence of this hormone in the urine indicates that you are pregnant.

The best time to test whether you are pregnant is 7-10 days after conception.


How to read home pregnancy tests:

You always compare the Test (T) line to the Control (C) line.


A positive result:

This indicates that the hCG hormone is present in your urine and you are pregnant. This occurs when the Test (T) line is the same colour as the Control (C) line.


A negative result:

 This Indicates that the hCG hormone is NOT present in your urine and you are NOT pregnant. The result is negative when the Test (T) line is not visible or is lighter than the Control (C) line. When this result is generated you should retest to confirm that it is not a false negative result.


False Negative result:

This occurs when the test generates a negative result when you are in fact pregnant. This can occur as a result of the following.

Taking the test too early: hCH levels increase exponentially during the first trimester. You may have a false negative result as the level of hCG is too low to be picked up by the pregnancy test. We advise you confirm your result with another test.

Diluted urine. If you are well hydrated there might be a lower concentration of this hormone in your urine and so there is not enough hCG per unit of urine tested.

Damaged test: The test may be damaged due to excessive heat and may not read the results correctly

Medications: Some drugs like as diuretics or promethazine (an anti-histamine) may cause a false negative result.



False Positive result:

This occurs when a positive result is present when you in fact are not pregnant. This can take place due to:

Certain medications: Anti-Parkinson drugs, anti-convulsion drugs and some tranquilisers may cause false positive results:

Protein or blood in the urine: as a result of cysts or infections or kidney damage

Chemical pregnancy: 25% of all pregnancies are chemical pregnancies, also called early miscarriage. A chemical pregnancy occurs when the pregnancy is lost shortly after implantation.


Buying a pregnancy testPredictorEarlyBox 2

When buying your pregnancy test it is vital use the most sensitive and accurate test.

Predictor standard pregnancy test measures 25mIU/ml and is 99% accurate 

Predictor early pregnancy test measures a low level of 12mIU/ml.

The early test is 90% accurate 4 days before your menstruation and 99% accurate the day of your expected menstruation.


Predictor Early Plus contains both the standard and the early pregnancy tests, allowing you test at the lowest level and confirm the result with a less sensitive but just as accurate test.You can now use a pregnancy test and trust the result




Baby Med. http://www.babymed.com/pregnancy-testing/false-positive-pregnancy-test-result

Better Health Chanel. http://www.betterhealth.vic.gov.au/bhcv2/bhcarticles.nsf/pages/Pregnancy_testing?open

The pregnancy lab. http://www.pregnancylab.net/2011/05/false-negative-pregnancy-tests.html

Lab Tests Online. http://labtestsonline.org/understanding/analytes/hcg/tab/test/

com http://www.birth.com.au/tests-offered-during-pregnancy/urine-tests#.VOXOTfmUe5J

Baby Hopes. http://www.babyhopes.com/articles/falsepositive.html