Lab tests in psychiatry
“Prudent prescribing: Intelligent use of lab tests and other diagnostics” (Current Psychiatry, October 2004) effectively reviewed key principles for using diagnostic and monitoring tools in psychiatry.
At a time when psychologists in some states have gained or may soon gain prescribing privileges, we as psychiatrists must embrace our medical training and apply our understanding of laboratory testing and diagnostic studies to our patients’ advantage. Outpatient laboratory testing is often difficult to coordinate, mostly because we traditionally have saved such tests for rare and unusual cases. As our use of such testing expands, we will more efficiently coordinate sample collection and report results to provide safe, effective medical care.
Also, more laboratory tests will soon be available. For example, the FDA recently approved a carbohydrate-deficient transferrin test to help clinicians detect or monitor an alcohol use disorder.
Regular and substantial alcohol use affects liver metabolism and transferrin synthesis, causing an abnormal, carbohydrate-deficient form of transferrin to be released into the bloodstream. Abnormal transferrin is measured as a percentage of overall transferrin in the bloodstream (%CDT). Any increase in %CDT above the normal range indicates a clinically significant increase in drinking. We consider 2.6 the upper limit of normal.
The test detects %CDT elevations in patients who have consumed 60 to 80 grams of alcohol (4 to 6 standard drinks) daily for 2 to 3 weeks. The test offers 90% to 95% specificity, with false elevations coming from inborn errors of glycoprotein metabolism (1% to 2% of the population) and in some cases from severe liver disease. Sensitivity is approximately 60% but improves significantly when the test is correlated with gamma-glutamyltransferase (GGT) testing and other serum markers.
Jeffrey S. Cluver, MD
Assistant professor of psychiatry
Ralph H. Johnson Veterans Affairs
Medical Center Medical University of South Carolina,
- Anton RF, Lieber C, Tabakoff B, for the CDTect Study Group. Carbohydrate-deficient transferrin and gamma-glutamyltransferase for the detection and monitoring of alcohol use: results from a multisite study. Alcohol Clin Exp Res 2002;26:1215–22.
- Conigrave KM, Degenhardt LJ, Whitfield JB, et al, for the WHO/ ISBRA Study Group. CDT, GGT, and AST as markers of alcohol use: the WHO/ISBRA Collaborative Project. Alcohol Clin Exp Res 2002;26:332–9.