Turnaround times
The quoted turnaround time is from sample receipt in the laboratory, to results authorisation in the Laboratory Information Management system. The times do not include transport of specimen to the laboratory or the administrative process to print and post/email reports. Service users must allow for transport and reporting time when ordering tests.
Clinical background:
Circulating cortisol levels follow a diurnal pattern in healthy individuals with the highest levels seen in the morning after waking and the lowest in the evening. Disorders of the hypothalamic-pituitary-adrenal axis override this diurnal pattern. Cushing’s syndrome is caused by increased production of cortisol due to either primary or secondary adrenal hyperfunction. Causes of primary adrenal hyperfunction are adrenal tumours and nodular adrenal hyperplasia. Secondary adrenal hyperfunction is caused by pituitary overproduction of ACTH or ectopic production of ACTH/CRH by a tumour. Increased cortisol levels are induced by pregnancy and by stress due to depression, trauma, surgery, hypoglycaemia, alcoholism, uncontrolled diabetes and starvation. Cortisol circulates largely (90-95%) protein bound to corticosteroid binding globulin (CBG) and albumin. The hormone is metabolised by the liver to form a number of metabolically inactive products, which are excreted in urine mainly in the form of conjugated metabolites. About 1% is excreted unchanged in the urine. This is the urinary “free” cortisol and reflects the concentrations of circulating non protein-bound cortisol. A 24-hour urinary cortisol measurement is one of the tests used in initial screening for Cushing’s syndrome because it provides an assessment of cortisol production that is not affected by diurnal variation (as is the case for untimed serum cortisol measurements).
Specimen container paediatric:
Urine, 24h (no preservative)
Specimen container adult:
Urine, 24h (no preservative)
Minimum volume paediatric:
1 mL urine
Minimum volume adult:
1 mL urine
Special requirements:
Accurate timing of the urine collection is required. Keep collection bottle refrigerated between bladder voidings if possible.
Sample stability:
7 days at 4 to 8°C,
1 month at -20°C
Transport requirements:
Ambient
Interpretation:
False-positive elevations of UFC may be seen in a number of conditions such as high fluid intake (>5 litres per day), depression and other psychiatric conditions, alcohol dependence, poorly controlled diabetes mellitus, physical stress (e.g. pain, surgery), malnutrition, intense chronic exercise.
False-negatives may occur in renal failure (creatinine clearance less than 60mL/min, with UFC concentrations falling with declining renal filtration rates), cyclical Cushing’s during periods of disease inactivity and in some cases of mild Cushing’s.
Reference ranges:
Less than 132 nmol/24h
Factors affecting result:
Inaccurate timing of 24 hour urine collection will impair the accuracy of estimation of 24hr urine cortisol excretion.
Exogenous glucocorticoid therapy may suppress endogenous cortisol secretion. A mass spectrometry assay is now in use, which is less susceptible to interference compared to immunoassay methods.