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Measurement of urinary excretion of endogenous and exogenous glucocorticoids

Author
Lynnette K Nieman, MD
Section Editor
André Lacroix, MD
Deputy Editor
Kathryn A Martin, MD

INTRODUCTION

Measurement of urinary excretion of corticosteroid (any steroid hormone produced by the adrenal cortex) metabolites has been used to evaluate adrenal function for many years. However, measurement of urinary cortisol excretion is more sensitive for the diagnosis of hypercortisolism and has largely supplanted the older assays. Evaluating daily urinary cortisol (and corticosteroid) excretion has the advantage of providing an integrated index of steroid production over a period of 24 hours, whereas measurements of serum cortisol only provide information about an instant in time. This is important because adrenocorticotropic hormone (ACTH) and cortisol are secreted in discrete pulses, resulting in plasma concentrations that rise and fall episodically. This is true not only for normal subjects but also for some patients with Cushing's disease and a few patients with Cushing's syndrome caused by adrenal tumors or ectopic ACTH secretion [1-4].

The measurement of urinary excretion of endogenous and exogenous glucocorticoids will be reviewed here. Other methods of cortisol measurement are discussed separately. (See "Measurement of cortisol in serum and saliva" and "Basic principles in the laboratory evaluation of adrenocortical function".)

URINE COLLECTION

The validity of the results is critically dependent upon normal renal function [5]. Individuals with moderate (creatinine clearance less than 60 mL/min) and severe renal impairment (creatinine clearance less than 20 mL/min) have progressively less cortisol excretion.

Additionally, over or under-collection of the 24-hour specimen can bias the results. Because of this, measurement of cortisol excretion must include concurrent measurement of creatinine excretion. The completeness of the collection (and the reproducibility of a series of collections) can be estimated from knowledge of the normal rate of creatinine excretion (which is equal to creatinine production in the steady state). In adults under the age of 50 years, daily creatinine excretion should be 20 to 25 mg/kg (177 to 221 mmol/kg) lean body weight in men and 15 to 20 mg/kg (133 to 177 mmol/kg) lean body weight in women.

From the ages of 50 to 90 years, there is a progressive 50 percent decline in creatinine excretion (to about 10 mg/kg in men), due primarily to a fall in muscle mass (see "Calculation of the creatinine clearance"). However, the excretion of cortisol and its metabolites varies diurnally whereas creatinine excretion does not. Thus, inadequate urine collections cannot be corrected on the basis of the creatinine value. Furthermore, creatinine excretion is not affected by fluid intake, while cortisol excretion increases with increased fluid intake [6]. The importance of adequate collection should be stressed to the patient. (See "Patient education: Collection of a 24-hour urine specimen (Beyond the Basics)".)

                

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Literature review current through: Nov 2016. | This topic last updated: Wed Dec 05 00:00:00 GMT 2012.
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