The Cortisol Test Your Doctor Skips

Sara Szal MD

I am starting something new this week. Every Friday, one number. One lab test or value that matters, explained in a few paragraphs.

My medical training taught me to wrap every piece of information in caveats and disclaimers before a woman ever got to the part she needed. I am done doing that here on Substack.

If the one number earns a place on your reading list, kindly forward it to one woman who is holding a symptom or a lab result she is having trouble decoding.

Reply and tell me which number you want next. I will run whichever you ask for the most.

Thank you for being here on The Female Edge.

She was 43, and told me the same thing I hear from hundreds of women a month in my precision medicine practice: I feel fine in the morning but I’m running on fumes by 3 or 4 p.m., and then wide awake at 10 p.m. when I need to go to bed.

She read my book, The Hormone Cure, a New York Times bestseller, and convinced her doctor to check her morning cortisol level. He did it grudgingly and called it normal. It was 8 mcg/dL.

That is not the cortisol of a healthy stress response. It’s low. I like to see it between 10 to 15.

Additionally, a single blood test is just one point on a curve. Cortisol doesn’t always hold still, so a single level is not always the whole truth.

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What I was taught in my medical training: Cortisol testing isn’t helpful unless you have a patient in whom you suspect Addison’s disease (complete failure of the adrenal glands, an autoimmune disease), or Cushing’s syndrome (extreme excess of cortisol). I was trained to identify the dead plants in the garden, not to look for early or subtle signs of ailing to come.

What I now understand: Cortisol is an important laboratory marker. One number is a basic screening test of total cortisol, but the more important picture is the shape, the rhythm across your day, and a single blood draw only captures one frame of the moving picture.

When we ran Susannah’s five-point cortisol test, she collected a sample at home when she woke up in the morning, 30 minutes later, 60 minutes later, afternoon, and night. Her pattern was specific. It wasn’t the wired-but-tired pattern, the runaway train of cortisol climbing all day on caffeine and adrenaline.

Susannah’s pattern was closer to a car running on an empty tank: every level of cortisol that we measured was below where it should be. Her “cortisol awakening response” was so low was really no response at all.

That’s the version of low cortisol that most women never hear about, because their doctor doesn’t know about it. Their doctor unwillingly orders one blood test and compares it to a wide range and reads it as technically normal.

I believe a flattened cortisol curve deserves the same clinical seriousness as other drifting biomarkers. Whether you have a high cortisol level (morning total cortisol > 15) or low cortisol, your adrenal glands are telling you there’s a potential problem. The stress response system that is supposed to rise to meet your day is not rising the way it should be.

The exception: a single low reading on a hard day is not a diagnosis, it’s evidence that you may want to look further. The flattened cortisol pattern reflects exhaustion that outlasts whatever caused it.

If your doctor refuses to check your cortisol, or does a single test and tells you you’re fine, use this reference range I’ve provided of optimal cortisol of 10 to 15 mcg/dL in the morning. If you have been told you were fine when you didn’t feel fine, restock this post. And please reply before to let me know which numbers you want unpacked next. Estrogen? Testosterone? Anti-Mullerian Hormone? Thyroid? Insulin, lipoprotein(a), ApoB, ApoE?

xo, Dr. Sara