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Endocrine Care: Bindu Chamarthi, Nikheel S. Kolatkar, Steven C. Hunt, Jonathan S. Williams, Ellen W. Seely, Nancy J. Brown, Laine J. Murphey, Xavier Jeunemaitre, and Gordon H. Williams Urinary Free Cortisol: An Intermediate Phenotype and a Potential Genetic Marker for a Salt-Resistant Subset of Essential Hypertension J Clin Endocrinol Metab 2007; 92: 1340-1346 [Abstract] [Full text] [PDF]

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Response to: Commercial assays for urinary free cortisol do not measure cortisol accurately

Bindu Chamarthi, Gordon H. Williams   (22 May 2007)

Commercial assays for urinary free cortisol do not measure cortisol accurately

Beverley E. Pearson Murphy, Departments of Medicine, Obstetrics & Gynecology, Psychiatry   (22 May 2007)

Response to: Commercial assays for urinary free cortisol do not measure cortisol accurately 22 May 2007
Bindu Chamarthi Brigham and Women’s Hospital/Harvard Medical School, Gordon H. Williams Send letter to journal: Re: Response to: Commercial assays for urinary free cortisol do not measure cortisol accurately GWILLIAMS{at}PARTNERS.ORG Bindu Chamarthi, et al.	We agree that HPLC is a more specific method for measuring urinary free cortisol (UFC) with less potential for cross-reactivity than RIA. However, it is important to note that even though the actual levels were different, in our subset of subjects who had UFC measured by HPLC as well,the results were consistent with regards to the high-mode group having higher UFC than the low-mode group. We agree that it is possible for some other factor to be assayed by the urinary cortisol assays, and we have reviewed this possibility in our paper under the discussion. However, the consistency of the findings by HPLC as well, supports that there truly is a subset of hypertensives with high-mode UFC levels and further studies are warranted to identify the mechanism(s) driving this.
Commercial assays for urinary free cortisol do not measure cortisol accurately 22 May 2007
Beverley E. Pearson Murphy, physician scientist McGill University, Departments of Medicine, Obstetrics & Gynecology, Psychiatry Send letter to journal: Re: Commercial assays for urinary free cortisol do not measure cortisol accurately bev.murphy{at}mcgill.ca Beverley E. Pearson Murphy, et al.	In their article on urinary free cortisol (UFC) as a potential genetic marker for a salt-resistant subset of essential hypertension (1), Chamarthi et al. obtained a mean value of 34.2 µg/day in subjects taking low sodium and 55.5 µg/day in those on a high sodium diet, giving an average of 44.8 µg/day for normotensive subjects (124 nmol/day). The method used was the Coat-a-Count RIA, Diagnostic Products Corp., Los Angeles, CA. Higher values of UFC were seen in the high sodium groups for both hypertensive and normal subjects, although no differences were seen in serum cortisol levels. These values for UFC are slightly more than twice as high as the average value for urinary cortisol in normal subjects (21.6 µg/day, or 57 nmol/day) obtained using methods involving detailed chromatography (2-4). Urinary cortisone was measured and was also higher in the high salt groups. Since cortisone is said to cross-react less than 1% in the method used, some other substance(s) must account for the high UFC values. Thus it is important to define just what is being measured by the method used here, in order to interpret the results. References 1. Chamarthi B, Kolatkar NS, Hunt SC, Williams JS, Seely EW, Brown NJ, Murphey LJ, Jeunemaitre X, Williams GH. 2007. Urinary Free Cortisol: An Intermediate Phenotype and a Potential Genetic Marker for a Salt-Resistant Subset of Essential Hypertension. J Clin Endocrinol Metab 92:1340-1346 2. Murphy BEP. 2004. Commercial radioimmunoassays do not measure urinary free cortisol accurately and should not be used for physiological studies. J Clin Endocrinol Metab 88:4001-4004 3. Murphy BEP. 2002. Urinary free cortisol determinations: what they measure. Endocrinologist 12: 143-150 4. Murphy BEP. 2000. How much ‘UFC” is really cortisol? (Editorial) Clin Chem 46:793