Replacing creatinine measurements with specific gravity values to adjust urine cotinine concentrations

Area of Science:

• Environmental Health
• Biochemistry
• Pediatric Pulmonology

Background:

• Urine cotinine concentration is a biomarker for environmental tobacco smoke (ETS) exposure.
• Adjusting cotinine levels for urine concentration is crucial for accurate exposure assessment.
• Creatinine is commonly used to correct for urine dilution, but specific gravity is an alternative.

Purpose of the Study:

• To compare the effectiveness of creatinine versus specific gravity in correcting urine cotinine measurements.
• To evaluate the impact of these corrections on the correlation with clinical endpoints, specifically pulmonary function in children with asthma.

Main Methods:

• Urine samples from nonsmoking children with asthma were analyzed for cotinine.
• Measurements were corrected for urine concentration using either creatinine or specific gravity.
• Pulmonary function tests were used as clinical endpoints.
• Reported ETS exposure was also assessed.

Main Results:

• Both creatinine and specific gravity corrections comparably reduced the variance in urine cotinine measurements.
• Corrected urine cotinine measurements showed improved correlation with pulmonary function compared to uncorrected values.
• Specific gravity-corrected cotinine performed as well as or better than creatinine-corrected cotinine in assessing lung function and ETS exposure.
• A more consistent dose-response relationship between cotinine levels and lung function was observed after correction.

Conclusions:

• Specific gravity is a reliable and effective alternative to creatinine for adjusting urine cotinine concentrations.
• Using specific gravity for correction enhances the utility of urine cotinine in research and clinical settings for assessing ETS exposure and its health effects.
• This method improves the assessment of environmental tobacco smoke exposure's impact on pediatric asthma and lung function.