So What Exactly Is A CDT Blood Test?

One thing about keyboard warriors is that they can confuse the layman by their creative but often inaccurate writing. This has led to confusion about CDT blood testing for the assessment of alcoholism.

First off, alcoholism is bad! It results in terrible behaviour issues with equally terrible illnesses such as cancer (oesophagus, breast, liver and throat) heart disease, liver disease, diabetes and a whole host of other medical diseases. With reference to drivers, it results in poor reaction times, affects judgement and self reason, gives false confidence and makes drivers lose their inhibitions. As a motorbiker, the last thing I want sharing my roads is a driver with all these impairments.

So how does the DVLA pick up a driver with a drinking problem who is a potential risk to themselves and other road users? In March 2011, the DVLA Medical Panel agreed that 'CDT

would become the sole test for assessing harmful use of alcohol in the HRO population....' They reached this decision after contracting Kings College London to research the use of biomarkers for High Risk Offenders (HROs) who made the following conclusion.

“CDT is reliable enough on its own to support a diagnosis of alcohol dependence, harmful or hazardous use, and has the advantage that common medications seem to have no influence on the performance of this biomarker”

So what exactly is this blood test that freaks all banned drivers doing their HRO medical?

CDT stands for Carbohydrate Deficiency Transferrin - a glycoprotein found in the liver as part of a complex reaction involving oligosaccharide N-glycan chains well outside the scope of this blog. However, excessive consumption of alcohol over time causes an increase in the disialo-transferrin isoform component with a consequent increment in the percentage value of CDT, (%CDT). It is this %CDT that the DVLA is interested in.

To see a rise %CDT the drinking has be over an extended time and usually around 50g (roughly 7 units) per day for at least a week. But remember not everyone processes alcohol at the same rate so this is only an approximation. So to ensure a normal CDT blood test abstaining is really the best policy. In subsequent blogs we'll explore how to why CDT is better than GGT and other biomarkers and what levels HROs going for their DVLA HRO medical should aim for.