[Ahem] Ok let me explain…Several catch-cries from Australian ads have earnt themselves a lifelong place in my head and heart, taking up space where something more important should be, no doubt, but does anyone remember this SPC canned fruit (REALLY showing my age now!!) one, where the little boy chases the grape around the bowl and declares it a, ‘Slippery Little Sucker!’? Ok so this little boy is every one of us when we’re trying to ‘capture someone’s cortisol’ and just like the boy we will eventually achieve a ‘result’ – get a ‘number’ but what in fact does this mean in relation to your patient’s HPA axis, stress perception, responsivity, recovery etc etc?
Recently I was presented with 2 cortisol results for a patient taken within the same 24hrs – her blood am result was above range, while her 24hr urine flagged under-functioning of her HPA axis generally.
Both were accurate.
Had I have only have seen one, I would have formed the wrong opinion and only gleaned part of her overall HPA story. Every different type of cortisol capture – from different mediums: blood, saliva & urine – to different collection conditions: time of day, fasting V fed, specific stressor exposure etc answers a different question about our patient’s HPA axis. So to use any form of cortisol assessment well we need to start with 2 understandings: 1) it is a slippery little sucker indeed and no one test can answer all our questions – or as Miller & colleagues more eloquently put it, “Remember, all models are wrong; the practical question is, how wrong do they have to be to not to be useful” and 2) be clear about the most important question you have about your patient you are trying to answer and that will make your choice of test (& timing & & &) patent. But do you know enough about cortisol regulation to be clear about the ‘sweet spot’ of each test?
The Cortisol Awakening Response has understandably attracted the bulk of the research focus over the last decade and accordingly has risen in popularity in practice & while it remains a very valuable way to answer certain questions about patients, our understanding of its limitations continue to grow. For example there is a disconnect between CAR & diurnal cortisol secretion – so in essence your CAR can look woke but your ‘Slope’ may be broke! If you’re a fan of this method, make sure you catch up on the CAR-Expert Consensus Guidelines by Stalder et al and if you’d like to get clear about which test and when, when it comes to all the key options for Cortisol Capture..
then let’s dive in together with my latest Update in Under 30 instalment 
Cortisol – Have You Been Caught Out?
I have! And just recently a stark contrast between the results from 2 different methods of cortisol capture in the same patient illustrated just how likely this is. How do we ‘capture’ something so ‘dynamic’ and interpret anything of substance from a ‘static’ assessment technique? But rather than throw up our hands and throw out the whole attempt to measure cortisol, we can improve the rigor, reliability and real-world meaningfulness of our patients’ results by refining our timing of tests, choosing the medium wisely & manipulating test conditions to answer specific questions about their HPA function. Great desktop reference included!