A comparison of creatinine vs. specific gravity to correct for urinary dilution of cotinine

Context: The validity of urinary correction standards has not been established for most analytes. Methods: We compared urinary creatinine and specific gravity as dilution correction standards for cotinine in a community-based study of smokers. Results: Models of blood cotinine regressed against CR or SG (measured by total soluble solids) significantly improved the fit compared to a model without a dilution measure (P < 0.01). There were no differences in model fit between CR- and SG-corrected values. Both CR and SG were significant predictors of urinary cotinine regressed against cigarettes smoked per day (P < 0.01). Conclusion: CR and SG are valid and interchangeable correction standards.