Factitious diarrhea induced by stimulant laxatives: accuracy of diagnosis by a clinical reference laboratory using thin layer chromatography.
BACKGROUND
Surreptitious ingestion of laxatives can lead to serious factitious diseases that are difficult to diagnose. Most cases involve ingestion of bisacodyl or senna. Thin layer chromatography (TLC) of urine or stool is the only commercially available test for these laxatives. Such testing is considered highly reliable, but its accuracy in clinical practice is unknown. Our aim was to evaluate the reliability of TLC laxative testing by a clinical reference laboratory in the United States.


METHODS
Diarrhea was induced in healthy volunteers by ingestion of bisacodyl, senna, or a control laxative (n = 11 for each laxative group). Samples of urine and diarrheal stool were sent in blinded fashion to the clinical reference laboratory for bisacodyl and senna analysis.


RESULTS
TLC testing for bisacodyl-induced diarrhea revealed a sensitivity of 73% and specificity of 91% when urine was tested and sensitivity and specificity of 91% and 96%, respectively, when stool was analyzed. When diarrhea was induced by senna, the TLC assay for senna failed to identify even a single urine or stool specimen as positive (zero% sensitivity).


CONCLUSIONS
Considering the expected prevalence of surreptitious laxative abuse in patients with chronic idiopathic diarrhea (2.4%-25%, depending on the clinical setting), TLC of urine or stool for bisacodyl by this reference laboratory would often produce misleading results, and testing for senna would have no clinical value. The major problems are false-positive tests for bisacodyl and false-negative tests for senna.
Shelton
Joseph H
JH
Baylor University Medical Center, Dallas, Texas, USA.
Santa Ana
Carol A
CA
Thompson
Donald R
DR
Emmett
Michael
M
Fordtran
John S
JS
D001726:Bisacodyl / Q000009:adverse effects / Q000032:analysis / Q000652:urine; D002400:Cathartics / Q000009:adverse effects* / Q000032:analysis*; D002855:Chromatography, Thin Layer; D019411:Clinical Laboratory Techniques / Q000592:standards*; D003967:Diarrhea / Q000139:chemically induced / Q000175:diagnosis*; D005162:Factitious Disorders / Q000139:chemically induced / Q000175:diagnosis*; D005188:False Negative Reactions; D005189:False Positive Reactions; D005243:Feces / Q000737:chemistry; D006801:Humans; D007753:Laboratories / Q000592:standards; D016013:Likelihood Functions; D012015:Reference Standards; D012676:Senna Extract / Q000009:adverse effects / Q000032:analysis / Q000652:urine; D012680:Sensitivity and Specificity
D002400:Cathartics; D001726:Bisacodyl; D012676:Senna Extract