medwireNews: Measurement of 24-hour urinary free cortisol (UFC) is highly specific for paediatric Cushing’s syndrome, say researchers.
The test was also very sensitive, at 89%, but did miss a few cases, report Helen Storr (Barts and the London School of Medicine and Dentistry, UK) and study co-authors.
They therefore advise further investigation if clinical suspicion remains despite a repeatedly normal test. “Measurement of midnight salivary cortisol may be a more appropriate alternative screening test for these difficult cases”, they write in Hormone Research in Paediatrics.
The team also suggests that the sensitivity could be improved by collecting urine over 3 consecutive days, although they note the problems inherent in achieving this with small children.
The study involved 66 children who were investigated for possible Cushing’s syndrome at an average age of 12.9 years. Forty-seven of these patients were diagnosed with Cushing’s syndrome, all but five of whom had above-normal 24-hour UFC values after correction for body surface area (BSA)
The eight patients diagnosed with primary pigmented nodular adrenocortical disease had higher absolute UFC values than the 39 with Cushing’s disease, but this difference disappeared after adjusting for BSA.
“Our results emphasise the need to take BSA into account when analysing 24-hour UFC concentrations”, say Storr et al.
All of the 19 patients who did not have Cushing’s syndrome had 24-hour UFC values within the normal range (40–340 nmol for immunoassay; <124 nmol for liquid chromatography-mass spectrometry), giving a specificity of 100%.
“The increasing incidence of obesity in the paediatric population is likely to lead to more investigations of patients with less extreme clinical features in general paediatric clinics”, say the researchers.
They add that the presenting features of Cushing’s syndrome in children “are variable and can be subtle”.
In this context, “it is useful to have a simple, reliable, non-invasive and inexpensive investigation, which provides information relevant to hypercortisolaemia”, the team concludes.
By Eleanor McDermid
Horm Res Paediatr 2016; Advance online publication
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