Cortisol 24-hour urine free

The presence of hypercortisolism can be established with a midnight plasma cortisol, late-night (11 PM) salivary cortisol, 24-hour urine free cortisol, and/or low-dose dexamethasone suppression test. 

Urinary free cortisol obtained from a 24-hour urine collection is an integrated measure of plasma free cortisol and eliminates the circadian influence on cortisol secretion. Urine free cortisol measurements are therefore considered to be the best screening test for hyperadrenocorticism. The urinary free cortisol excretion rate in normal subjects falls between 20 and 80[lg/day (Figure 51-9), The measurement of urinary 17-hydroxycorticosteroid excretion rates for determining adrenocortical hyperfunction is no longer recommended because of problems with method sensitivity and specificity. 

No abnormalities were found in Brian s urine and his blood cell count was normal. However, his blood glucose was 8.1 mmol l-1 (normal value 3.5-6.7 mmol l-1) and a glucose tolerance test later indicated impaired glucose tolerance. Tests for plasma insulin and thyroid hormones (T3, T4 and TSH) showed normal levels. Two further tests were then performed. A 24-hour urine sample was collected and Brian s free cortisol excretion was found to be considerably higher than normal. A second test, the dexamethasone suppression test, was also carried out. In this test, the patient is given a dose of dexamethasone at 11 -12 p.m. and plasma cortisol is measured early next morning. 

The different methods of assessing hypothalamic-pituitary-adrenal axis activity in patients using inhaled glucocorticoids have been compared (35). The AUC of serum cortisol concentrations was the most reliable method. There were significant positive correlations between AUC and the 8 a.m. serum and salivary cortisol concentrations. The authors favored the non-invasive method of salivary concentration measurement. However, 24-hour urine collection is not recommended, as it correlated only moderately well. This finding is consistent with the results of other studies. Urinary free-cortisol estimation based on immunoassay after inhaled glucocorticoids may be an unreliable surrogate marker of... 

Procedure Twenty-four-hour urine samples are collected daily for 4 consecutive days. Dexamethasone, 0.5 mg, is given orally every 6 hours starting at 0800 hours on day 2 (for a total of 8 doses). Free cortisol, 17-hydroxycorticosteroids, and creatinine are measured in each 24-hour urine sample. Other measurements include serum cortisol determinations on day 1 (at 0800 hours and 2000 hours) to look for diurnal variation and on day 5 (at 0800 hours). 

Serum or plasma (with heparin as an anticoagulant) can be used. No special handling procedures are necessary, and specimens may be stored refrigerated overnight at 2 °C to 8 °C. Freezing is preferred for long-term stability. Urinary free cortisol is determined on a 24-hour urine collection with or without boric acid preservative. If collected without preservative, the specimen should be refrigerated between collections and an aliquot frozen immediately after completion of the 24-hour collection. 

Urine Specimens. A complete 24-hour urine specimen is collected with 10 g of boric acid to maintain the urine pH below 7.5. Urine should be refrigerated during the collection period. After measuring the total volume, a thoroughly mixed aliquot ( 10mL) is stored frozen at -20 °C. Care should be taken to ensure an appropriately timed, complete 24-hour collection because an incorrectly timed sample is the largest source of error with this method. Free cortisol determinations on randomly collected urines are discouraged because of the variation and pulsatile characteristic of cortisol secretion. 

Hour urinary Collect urine over 24 Urinary free cortisol greater Easy to perform but should not be used... 

The following are representative values for free cortisol excreted per 24 hours in urine ... 

Elevated urinary free cortisol concentrations are highly suggestive of Cushing s syndrome. Normal reference values for urinary free cortisol are 20 to 90 meg per 24-hour period. It is not unusual to detect a twofold or threefold increase in urine cortisol in the patient with hyperfunction of the adrenal gland. Starvation, topical steroid application, hydration from water loading, and acute stress aU are capable of elevating the urine cortisol concentrations. Because other pathologic conditions can increase the amount of free cortisol, additional... 

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