Endocrine Abstracts

Background: The use of salivary cortisol is well validated in the diagnosis of Cushing’s syndrome but routine use of salivary measurements during dynamic tests of HPA axis sufficiency is uncommon and reference ranges are not established. Salivary cortisol (SalF) and cortisone (SalE) measurements by LC–MS have several advantages including ease of collection and more accurate reflection of unbound serum cortisol levels in conditions of altered CBG levels (e.g. oestrogen replacement). SalE may have advantages over SalF although this remains to be confirmed.

Method: A retrospective analysis was carried out of the SST results from patients tested at the Christie Hospital NHS Foundation Trust since September 2010. Some data from a previous study were also included. Patients were subdivided by their use of oestrogen-containing medications. SalF and SalE values from 30 to 60 min post-synacthen (250 μg) were plotted against SerF in order to derive reference ranges. Salivary values corresponding to a SerF of 450 nmol/l were calculated using a y=mx+c equation.

Results: Matched serum and salivary values at 30 and 60 min were available from 71 SSTs. Using a cut-off of 450 nmol/l for SerF at 30 min; SalF=14.3 nmol/l (n=64) and SalE=40.7 nmol/l (n=16). Using the same 450 nmol/l cut-off at 60 min; SalF=22.3 nmol/l (n=63) and SalE=50.6 nmol/l (n=16). The use of oestrogen did not significantly affect salivary measurements at either time point.

Conclusions: Novel 30- and 60-min cut offs for salivary SST results are presented, which now require further validation in clinical practice. The use of oestrogen did not lead to significant differences in salivary cortisol or cortisone values. It is important to develop robust reference ranges for steroid measurement by LC–MS, particularly in saliva, as LC–MS steroid measurement is expected to become mandatory in view of the shortfalls of steroid immunoassays.