The acronym CDT in medical contexts most frequently refers to Carbohydrate-Deficient Transferrin. This term identifies a specialized blood test that serves as a biomarker for chronic, heavy alcohol consumption. Unlike tests that measure alcohol at a single point in time, the CDT assay provides insight into drinking patterns sustained over a period of weeks. Understanding this definition is important, as the test is widely applied in various medical, legal, and occupational settings.
Carbohydrate-Deficient Transferrin
Transferrin is a protein synthesized in the liver that transports iron throughout the bloodstream. This transport protein is a glycoprotein, meaning it naturally has carbohydrate structures attached to its core. A healthy individual’s transferrin typically possesses three to five of these chains.
Chronic, excessive alcohol intake interferes with the attachment process, known as glycosylation. When this process is disrupted, a higher proportion of the protein circulates with fewer than the normal number of chains. This altered form is defined as Carbohydrate-Deficient Transferrin. The test measures the percentage of this deficient form relative to the total transferrin in the blood.
Using CDT for Detection of Chronic Alcohol Consumption
The CDT test is specifically designed to detect sustained heavy drinking, typically defined as consuming 50 to 80 grams of pure alcohol per day for at least two weeks. This level of consumption is equivalent to about four to six standard drinks daily. The test is not useful for detecting a single instance of intoxication or occasional binge drinking.
Because the half-life of transferrin in the blood is approximately two weeks, the CDT level reflects a person’s average alcohol intake over the preceding two to four weeks. This longer detection window provides a much more objective measure of a pattern of misuse compared to breathalyzer tests. The CDT test is often utilized in situations where objective evidence of long-term sobriety or consumption is needed, such as in monitoring patients undergoing addiction treatment or in forensic and occupational health evaluations.
The mechanism by which alcohol increases CDT involves the disruption of liver enzymes, particularly those that regulate the addition and removal of the carbohydrate side chains. High alcohol levels can inhibit the enzyme that adds the chains (glycosyltransferase) while potentially stimulating the enzyme that removes them. This imbalance leads to the measurable increase in the carbohydrate-deficient isoforms.
Interpreting CDT Test Results
CDT results are generally reported as a percentage, indicating the proportion of carbohydrate-deficient transferrin to the total transferrin in the blood. For many laboratories, a result below 1.7% is considered within the normal range for non-drinkers or moderate drinkers. However, this cut-off point can vary slightly based on the specific laboratory method used.
A result exceeding the established cut-off, such as above 1.7%, suggests prolonged heavy alcohol consumption. When a person ceases heavy drinking, their CDT levels will gradually decrease, typically returning to the normal range within two to four weeks. This decline makes it a useful marker for monitoring abstinence or significant reduction in alcohol intake over time.
Interpreting the test requires considering potential factors unrelated to alcohol that can cause an elevated CDT result, leading to a false positive. Certain liver diseases, such as severe hepatitis or liver cancer, can disrupt the liver’s ability to produce fully glycosylated transferrin. Furthermore, rare genetic conditions, such as congenital disorders of glycosylation or certain transferrin variants, can also cause elevated CDT percentages. Therefore, a healthcare professional must evaluate the CDT result in combination with the patient’s full medical history and other laboratory markers, such as Gamma-Glutamyl Transferase (GGT), for an accurate diagnosis.
Other Common Medical Definitions
While Carbohydrate-Deficient Transferrin is the main medical context, the acronym CDT also represents other distinct concepts:
- In dentistry, CDT stands for Current Dental Terminology, the official code set used for reporting dental procedures and services to third-party payers. This coding system is updated annually by the American Dental Association.
- In infectious disease, CDT refers to Cytolethal Distending Toxin, a bacterial toxin produced by Gram-negative bacteria that can cause cell cycle arrest and damage.
- In physical therapy, CDT is an abbreviation for Complete Decongestive Therapy, a specialized treatment regimen used for managing lymphedema, a condition involving chronic swelling.