The Pregnancy Test – How it Works and Why it is also a Cancer Indicator

Posted on Aug 15, 2013 in Cancer, Medical Rewind

Creation of the Pregnancy Indicator hCG in normal pregnancy

If you search for information on this topic you may be told things such as: “hCG is produced by the placenta and can be found in a woman’s system as soon as implantation of a fertilized egg has occurred”.

True enough, but if you want to understand the connection to cancer detection you have to look a bit deeper.

Once an egg is fertilised you have the earliest stage embryo, but an embryo cannot survive ‘floating free’ in the uterus. It has to implant itself in the wall of the uterus. How does it do that?

You have probably heard of embryonic stem cells which can be used to repair all sorts of different parts of our bodies? In pregnancy these stem cells are triggered by the presence of oestrogen (estrogen) to become ‘trophoblast’ cells. The trophoblast is a fast growing group of cells that attacks the lining of the uterus, enabling a place for the embryo to attach itself and leading to the creation of the placenta and umbilical cord.

The trophoblast gives off the hormone ‘human chorionic gonadotrophin’ or ‘hCG’ for short. hCG circulates in the blood stream and can be detected in the urine in tests that are 92% (or more) accurate. As the early pregnancy develops the amount of trophoblast increases and so does the level of hCG.

So until the embryo is becoming implanted in the uterus wall there will be no hCG to be detected and even after that in the early days there may not be enough hCG for some test kits to register its presence. Blood tests can detect lower levels of hCG, but the whole purpose of the urine tests is simplicity, cheapness and the ability to ‘do-it-yourself’ at home.

After the 56th day of pregnancy the baby’s new pancreas starts generating enzymes which help destroy the trophoblast. So in a normally progressing pregnancy the urine test should become ineffective (though you wouldn’t normally need to test after that time anyway so there’s probably little evidence of this effect!).

How the Pregnancy Test Kit Works

The test sticks have an absorbent tip (usually under a protective cap) and the test starts by you holding this tip in the stream of urine or, if you prefer, in a clean pot which you use to collect some urine as you pee.

The urine is then drawn up the absorbent strip into the body of the tester (like a wick or a tissue dipped into liquid). Here it comes across the first strip or marker where the presence of hCG causes a reaction to turn the strip blue (or other colour according to make of test kit). Further on a second strip/marker reacts with the urine (with or without any hCG in it) to show that the process has worked correctly.

This is the classic ‘one line not pregnant’ and ‘two lines pregnant’ test. Nowadays different makes of test kit can arrange things differently such as a + or – result or even the words ‘pregnant’ or ‘not pregnant’. You have to read the instructions with each brand to make sure you use and read the test kit correctly.

As indicated above, the amount of hCG present in your body grows as the early pregnancy progresses. So whether you get a positive result depends on how much hCG is needed to activate your particular tester and where you are in the early pregnancy. Testers have become more sensitive in recent years and some can detect pregnancy almost as soon as you have missed a period. Different brands work at different levels of sensitivity so again check the instructions.

Are They Always Right?

Not always, but mostly. The most common reason for a false reading is, reportedly, failure to use the test properly. This might be because different brands have slightly different requirements and the results need to be considered only within the recommended 3-5 minute window. Apart from that, you can get a ‘false negative’ by testing too soon using a test that is not sensitive enough. False positives can result from liver diseases or cancers.

How does a Pregnancy Test work as a Cancer Detection Method?

There is a theory that all cancers are fundamentally the same. This Unitarian or Trophoblastic Thesis of Cancer^2 is described in more detail on my page on causes of ovarian cancer.

In brief it explains that all cancers share the same origin (at a cellular level) as the trophoblast cells that are necessary in the start of pregnancy, but without the controlling body functions of a normal pregnancy that limit the trophoblast to its primary, positive function.

The most malignant cancers in women and men, respectively, are probably the primary^3 uterine and testicular chorionepitheliomas (ie the cancers starting in the surface tissue of the uterus or testes). The cells of these two cancers are indistinguishable from the normal pregnancy trophoblast.

As these cancer cells are the same as the pregnancy trophoblast they must generate the same hormone hCG, so the same test can detect these highly malignant cancers. Other tumours may have less ‘plain’ trophoblast and more ‘normal’ body cells in them and so will create less hCG (proportionately to their size).

It follows then, if this thesis is right, that:

  • If you test positive on a pregnancy test you are either pregnant or have cancer (no choice for the men!); and
  • The higher the hCG reading the more malignant the cancer.

Unfortunately a negative test does not necessarily mean you don’t have cancer. It just means that you don’t have cancer that is active (or malignant) enough to generate hCG that your particular pregnancy test kit can detect (the same as for a false negative for an actual pregnancy).

In the 1950 paper on the Unitarian Thesis2 the authors said that it was difficult to get a simple, reliable test for hCG levels. Part of the problem, they said, was that the most malignant testicular cancer could give over 1,000,000 IU (International Units) of hCG in a volume of urine, while other testicular cancers which are still strongly malignant and metatastic (ie able to spread (metastasize)) may give under 50 IU and less malignant, non-testicular cancers even less.

Modern pregnancy tests, however, react to levels around 50 mIU/mL or less (over 25mIU/mL and you are pregnant according to (ie 25 thousandths of one IU in one millilitre of urine). If a man has around 50 IU in say a typical full bladder of 500mL then that would still be 500 mIU/mL and so definitely detectable by modern pregnancy tests; but I don’t have figures for hCG levels associated with typical cancers to be certain.

Laboratory tests for hCG are more sensitive and can detect lower levels (whether testing for pregnancy or cancer) and can give a measurement of the AMOUNT of hCG in the urine sample. A series of measurements can also be used to indicate if any treatment is succeeding in reducing the malignancy or not.

The difference between testing for hCG and ca125 is that the hCG is produced by the trophoblast element of the tumour (ie the malignant element) whilst ca125 is produced by the ‘normal’ ovarian cells responding to the cancer or to some other stimulus. This is why ca125 is not a definitive test, but hCG is (or you are pregnant!).

What you can do

Try it out – Pregnancy test kits are not expensive. I know that the message on my web site can be hard to believe when your doctors are not telling you the same, but if you have already been diagnosed with cancer a positive result should give confidence in the science behind my writing.

If you are worried about having cancer, it is better to find out sooner rather than putting it off – and the ca 125 test is useful but not definitive.


1.  Ernst T Krebs Sr, Ernst T Krebs Jr and Howard H Beard, The Unitarian or Trophoblastic Thesis of Cancer, The Medical Record published July 1950.

2. Primary meaning the starting point for the cancer, not a secondary cancer spread from elsewhere in the body.