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April 13, 1984

Reliability of Measurements of Tricyclic Levels

Author Affiliations

University of South Carolina School of Medicine Columbia

JAMA. 1984;251(14):1833. doi:10.1001/jama.1984.03340380019007

To the Editor.—  In regard to the letter "Toxic Tricyclic Antidepressant Levels and the ECG,"1 several remarks are pertinent. In a previous discussion in The Journal,2 the reliability of tricyclic antidepressant serum levels were questioned. The laboratory procedures (gas or liquid chromatography) for measuring tricyclics are complicated, and specimen collection procedures also can be problematic.3 Also, studies using known standards and split samples have revealed troublesome interlaboratory and intralaboratory differences in reporting tricyclic levels.4,5 The patient described by Johnson and associates1 had an initial doxepin level of 1,230 ng/mL with no ECG changes. While it may be correct to conclude that this case is an exception to the "rule" that tricyclic levels over 1,000 ng/mL are associated with QRS prolongation, the alternative possibility of laboratory error must be considered. Another group of investigators using serum spiked with a known quantity of amitriptyline plus nortriptyline have reported