Low cortisol what does it mean if you have that?

Diurnal: Hi. Cortisol shows diurnal variation, so WHEN IN THE DAY it's measured is very important. Cortisol deficiency is uncommon. It can be truly low from adrenal or pituitary diseases; it can be artifactually low from low binding proteins in the blood or drawn at other times of the day. If you REALLY don't make enough cortisol, you may or may not make enough aldosterone. Treat deficiency with replacemnt

Adrenal insufficienc: People with adrenal insufficiency will have low cortisol levels. However, this is a very rare disorder. Just getting a random blood cortisol level is usually not of any value (saliva cortisol levels are worthless for this diagnosis). If you have symptoms of weight loss, loss of appetite, low blood pressure when standing, darkening of the skin, it is worth seeing an endocrinologist about it.