I had a blood test recently by an independent laboratory for insurance
purposes. I keep all copies of my blood work for the past 6 years.

When looking over their results to past blood work results by other
labs, I noticed that something called "CDT" was tested and it said
"CDT results confirmed by Western Blot Assay." My doctor was also
unfamiliar with "CDT" and called his lab (perhaps I need to get a new
doctor). I believe it is called Carb Deficit Transfer or something.
COuld you please tell me what CDT is and why I might have been tested
for this?

Thanks

CDT is "Carbohydrate Deficient Transferrin." Many insurance companies
use a CDT test to check for possible alcohol abuse in potential
clients.

"In the 1990s, two new tests were introduced into life insurance
medicine. They came to be known as alcohol markers, earning this
moniker because they were shown to have very high specificity for
abusive drinking. These two tests are known as carbohydrate-deficient
transferrin (CDT) and hemoglobin-associated acetaldehyde (HAA)... In a
recent informal survey of 30 major companies, this underwriter found
that 1 in 3 did not make use of alcohol markers as yet. There are
probably a number of reasons for this, one of which is the fact that
these tests are not yet widely utilized in health care. That may
change, however, now that one version of the CDT test has been
approved by the Food and Drug Administration for clinical use."

MyAssurenet
http://www.myassurenet.com/articles/hgeorge1100.html

"There are also 'special blood tests' that are used to clarify cases
of SAA [suspected alcohol abuse]. One of these is the CDT ( see this
link for a description and how it is used in SAA cases
http://www.labone.com/insurance/cdt.html )"

Risk Tutor
http://www.risktutor.com/demo/dec_01.html

"Carbohydrate-deficient transferrin (CDT) is an effective tool in the
search for the chronic alcohol abuser. The CDT test is performed on
serum samples in cases of suspected alcohol abuse. When elevated, CDT
can be indicative of chronic, excessive consumption of alcohol,
defined as at least 60 grams of alcohol per day on a routine basis for
a minimum of two or three weeks... Other causes of an elevated CDT
measurement include biliary cirrhosis and obstructive liver disease. "

Lab One
http://www.labone.com/insurance/cdt.html

Search terms used:

cdt
blood test
carbohydrate deficient transferrin
alcohol abuse
insurance

I hope this is helpful. If anything I've said is unclear or
incomplete, if more information is required, or if any of the links do
not function, please request clarification before rating my answer;
I'll be glad to offer further assistance.

Best regards,
pinkfreud

Just FYI:
The "Western blot" is a widespread technique for detecting the
presence of, and to some extent measuring the concentration of, a
protein of interest, in this case CDT.
It works by separating proteins from a sample according to their
molecular weight by passing them through a gel (usually acrylamide)
under the influence of an electric current.  The separated proteins
are then transferred to a membrane (just like a sheet of plastic
really), either PVDF or nitrocellulose, where they are immobilised
(this is the "blotting" step.  Note that they are still spread out
according to their molecular weight.  Then, an antibody that is
specific for the protein of interest is applied, and this is detected,
usually by attaching ANOTHER antibody to it that carries a useful
enzyme.  This enzyme is used to cause a reaction that either colours
the membrane, or causes light to be emitted.  The combination of the
position of the signal on the membrane, a function of the molecular
weight, and the specificity of the antibody pretty much identifies the
protein of interest.  The strength of the signal is a measure (albeit
coarse) of protein concentration.
BTW - it is called "Western" by analogy with the "Southern" blot - a
similar process for the detection of particular DNA segments -
developed by E. M. Southern.  Thee is also Northern blotting for RNA,
and far-western blotting!  So far - no Eastern blotting -
(carbohydrates maybe??)