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Laboratory Methods for Detecting Prenatal Exposure to Cocaine

Laboratory Methods for Detecting Prenatal Exposure to Cocaine. Roger L. Bertholf, Ph.D. Associate Professor of Pathology Chief of Clinical Chemistry & Toxicology University of Florida College of Medicine Health Science Center/Jacksonville. Why test babies for cocaine?.

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Laboratory Methods for Detecting Prenatal Exposure to Cocaine

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  1. Laboratory Methods for Detecting Prenatal Exposure to Cocaine Roger L. Bertholf, Ph.D. Associate Professor of Pathology Chief of Clinical Chemistry & Toxicology University of Florida College of Medicine Health Science Center/Jacksonville

  2. Why test babies for cocaine? • Prevalence of maternal cocaine use • Effect of in utero cocaine exposure on fetal and postnatal development • Medical/social/legal interventions

  3. Prevalence of maternal cocaine use • 1998 Household Survey revealed that 1.8 million Americans use cocaine (0.8% of population >12 years old) • 2% of 18-25 year-olds; 1.2% of 26-35 year-olds • 0.5% of women are cocaine users • Estimates of the prevalence of cocaine use during pregnancy range from less than 2% to more than 15% • Reasons for variations • Geographic/socioeconomic/racial • Methods used to detect use

  4. Is prenatal cocaine exposure harmful? • Extensive literature on clinical effects of prenatal cocaine exposure • Confounding factors are almost always present • Poor prenatal care • Concomitant drug use (alcohol, nicotine) • Reliable animal models do not exist • Sheep • Pig • Rodent

  5. Well documented physiological effects of cocaine • Vasoconstriction • Decreases uterine blood flow in sheep • Cerebral vasodilation and hypertension in newborn sheep and pigs • Neurotransmitter deficiencies • ACTH and corticosterone response in rats • Dopamine transporter binding in mice • Consistent observations in cocaine exposed neonates • Intrauterine growth retardation (LBW) • Prematurity • Complications/LOS

  6. Does cocaine cross the placenta? • Studies in pregnant sheep and rodents indicate that both cocaine and its metabolites cross the placenta • Fetal levels approximately 15% of maternal • There is also evidence that the placenta has AChE activity • May have a protective effect • Placental transfer of cocaine does not appear to be flow-limited • Cocaine can be measured in the amniotic fluid, but there is disagreement over whether it originates solely from fetal urine

  7. Other sources of cocaine exposure • Breast Milk • Passive inhalation • Intentional/accidental ingestion

  8. Detecting prenatal cocaine exposure: Analytical considerations • Cocaine metabolism • Quantitative thresholds • Choice of specimen

  9. Cocaine metabolism

  10. Cocaethylene

  11. Quantitative thresholds • For immunochemical methods, quantitative thresholds are established by calibration • Pure compound or mixture of isomers • Semi-quantitative results for real specimens • Purely quantitative results are only available using specific methods • GC/MS • HPLC • GC

  12. Detecting prenatal cocaine exposure: Methods • Immunochemical methods • RIA, ELISA • EMIT • FPIA • CEDIA • POC • Spectrometric methods • GC/MS • HPLC • GC

  13. Immunochemical methods • Most are calibrated to a threshold of 300 ng benzoylecgonine per mL of urine • Corresponds to the SAMHSA specifications • May be adapted to other specimens • Most are designed to measure benzoylecgonine in urine • Benzoylecgonine is not the principal metabolite in all specimens

  14. Chromatographic methods • Quantitative GC/MS analysis (by isotope dilution) is considered the reference method • Sensitivity <10 ng/mL • Requires extensive specimen preparation (extraction, derivatization, isotopically-labeled internal standards) • HPLC has similar sensitivity to GC/MS applications, but detection is less specific • Does not require preparation of volatile derivatives • GC is robust and sensitive, but lacks detector specificity • Nitrogen/Phosphorus detectors are very sensitive but expensive

  15. Detecting prenatal cocaine exposure:Specimens • Maternal specimens • Urine • Amniotic fluid • Hair • Neonatal specimens • Urine • Meconium • Hair • Nails

  16. Cocaine in maternal specimens • Maternal urine is easy to collect, and measurements are reliable • Usually reflects exposure within the past 2-3 days • Uncontaminated amniotic fluid is harder to obtain • More direct measure of fetal exposure (may be substitute for screening fetal urine) • Pharmacokinetics of cocaine and metabolites in amniotic fluid have not been established. • Hair is the most difficult specimen to analyze, but shows promise as a clinical specimen • Incorporation of cocaine in hair has been widely documented

  17. Cocaine in neonatal specimens • Urine • Sometimes difficult to collect • Can be extracted from diapers • Meconium • More difficult to collect uncontaminated specimens • Can also be extracted from diapers • Hair • Shows promise, but methods are not widely available • Nails • Most data on postmortem specimens

  18. Urine drug testing in neonates • Typically uses immunoassays configured for workplace drug testing • Positive threshold >300 ng/mL (benzoylecgonine) • Most studies indicate that neonatal urine drug screening at conventional thresholds fails to detect up to half of cocaine-exposed infants • Results of neonatal urine cocaine screening usually correlate with maternal urine

  19. Use of lower screening thresholds

  20. Urine collection from diapers • Several studies have documented the correlation between chemistry and microscopic laboratory results on bag-collected and diaper-extracted urine • Cocaine, benzoylecgonine, and ecgonine methyl ester can be extracted from diapers with methanol.

  21. Meconium drug testing The fetus swallows drug-laced amniotic fluid Drugs are deposited in the intestinal contents (or biliary excretion) Meconium, passed in the first bowel movement, contains drugs that have accumulated during the 2nd and 3rd trimesters

  22. Is meconium testing better than urine? • Several studies comparing urine and meconium results concluded that meconium testing was more sensitive • Analytical bias (RIA vs. EIA) • Cannot exclude the possibility of contamination • Studies using urine and meconium methods with comparable sensitivities have reported equivocal results

  23. Hair testing • Animal studies have demonstrated a dose-related cocaine and benzoylecgonine accumulation in hair • Cocaine and benzoylecgonine have been detected in hair specimens collected from cocaine abusing mothers and their infants • Potentially the most sensitive method

  24. Other specimens • Blood • Amniotic fluid • Breast milk • Saliva • Nails

  25. Distribution of cocaine metabolites

  26. Which specimens are most stable?

  27. Comparison of sensitivities

  28. Conclusions • Testing for prenatal cocaine exposure is widespread, but clinical indications are not well established • None of the methods currently available are capable of measuring the magnitude or duration of prenatal cocaine exposure • Urine screens must have greater analytical sensitivity to be useful for detecting prenatal cocaine exposure • Neonatal hair testing appears to offer the best clinical sensitivity

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