Things to know about test results and restrictions

It’s really important to understand these points when discussing test results and restrictions:

1.  Test Name.  Different test kits may name the test differently, normally only slight changes. Fortunately, there seems to be a common theme – simply “Chromogranin A” although some may abbreviate it to CgA or CHGA.  

2.  Results.  A positive result may indicate the presence of a tumour but will not tell the doctor what type it is or where it is.  Additionally, to amplify above, the quantity of CgA is not associated with the severity of a patient’s symptoms associated with one of the NET hormonal syndromes but is associated with the tumour burden – the mass of tumour.  Test results cannot be interpreted as absolute evidence for the presence or absence of malignant disease. Imaging and tissue sampling are usually a stronger indication. 

Results can differ between laboratories in terms of the unit of measure and the reference range.  This can cause havoc and misunderstandings in patient groups as people try to compare apples with pears.  Always know and state your lab data before asking the question in patient groups.  This is important so you can filter out the usual irrelevant responses you may receive.

When interpreting the result of the CgA blood test, caution is recommended, bearing in mind the multitude of factors that may lead to both false positive and negative results (as per controversy above). 

If concentrations of CgA are elevated prior to treatment and then fall, then treatment is likely to have been effective. If following treatment of the tumour concentrations begin to rise again, then the patient may have a recurrence of the tumour. As above, imaging remains a potentially stronger indication. 

Elevated CgA is a constant and somewhat excitable discussion point in patient forums and not just because of the confusion caused by not adding the unit of measurement when asking questions in a patient forum. Some people get quite excited about a single test result.  I refer to Dr Woltering et al where it clearly states that changes in CgA levels of more than 25% over baseline are considered significant and a trend in serial CgA levels over time has been proven to be a useful predictor of tumour growth (i.e. a single test result with an insignificant rise may not be important on its own).  Dr Woltering also gives good advice on marker tests when he says, “normal is normal” (i.e. an increased or decreased test result which is still in range is normal and not an indication of more or less growth).

3.  Restrictions.  Different test kits not only produce different testing score outputs (unit of measure and reference ranges) but there is the possibility of different testing constraints/restrictions. Other than the requirement to temporary halt PPIs, there are no major restrictions (but always obey your lab test instructions which should be provided before the test).  However, according to several sources (including Reference 3 below), patients should undergo an overnight fast (anything between 8-12 hours is mentioned). Reference 3 also mentions exercise, but an overnight fast would seem to suffice for both in most individual cases.  As above, always obey your lab test instructions which should be provided before the test.  

Note:  Healthcare organisations buy their test kits from commercial companies, there are several different test kits in use, each with potentially different instructions.  Labs may also have different processes for handling and storing.  Using the same lab is preferable but not always possible.