Why not just blood tests

Blood tests are extremely well established and a significant amount of data has been accumulated over many years, hence they are well understood. Unlike hair tests they cannot be adulterated or influenced by external or environmental factors and they also provide shorter defined periods over which they can identify excessive alcohol use.

Certain blood markers can also provide an indication as to whether there may have been a previous history of chronic alcohol abuse with resulting liver damage, this is very helpful since it provides an indication as to how serious the alcohol abuse might be and whether this is deep-seated or a more normal transient pattern. It also helps to understand the risk of re-occurrence, therefore blood tests make an essential contribution to alcohol testing. However being predominantly indirect markers they are less specific than hair tests, in that all the blood markers tested are affected by influences other than alcohol, with the exception of CDT, which has a very low false positive rate. Each marker is generally affected by different influences and therefore using a profile of several blood tests minimises this problem, but cannot eliminate it. Like the hair tests there is also inter-individual variability in response to these influences, therefore blood tests cannot always provide a reliable understanding of the amounts of alcohol consumed but become very useful when interpreted in the context of the results from hair tests.


Below are examples of the issues that can arise from using blood tests alone:

  • A range of commonly prescribed or pharmacy purchased medications such as Paracetamol and Statins can cause certain LFT’s to be raised above the normal range mimicking the effects of alcohol, certain diseases such as Hepatitis can also cause raised LFT’s like alcohol. If these results are taken out of context this can give rise to False Positive results.
  • CDT is more specific than the LFT’s and although it can become raised for other reasons, raised CDT is normally associated with excessive alcohol in >95% of cases. However it is less sensitive and is only raised in around 60% of males and 50% of women following excessive alcohol use over the recent 2 to 3 weeks. Again taken out of context this can give rise to False Negative results.
  • MCV (Mean Corpuscular Volume) is not a liver enzyme and is typically influenced by different factors than LFT’s and CDT, however as with the LFT’s and CDT it will not always be raised by excessive alcohol use and can become raised for certain conditions unrelated to alcohol. However when combined with the other blood markers it becomes a good indicator for excessive drinking.

Like hair testing, because of the various issues described above there are sometimes conflicts between the blood test results. When this occurs it can often be resolved by putting into context with the results from the hair tests. Without the addition of the hair tests, on a significant number of cases, the results would remain inconclusive.

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