🩸 Does a normal CBC rule out iron deficiency in women?

I've had more blood drawn this year than in the rest of my life put together. Okay, maybe that's an exaggeration, but it certainly feels that way.

I'm monitoring my own iron status, which means an iron panel every few weeks. I put a CBC on the order every single time. I have a stack of them now, which is how it dawned on me that I had been dutifully collecting a test I didn't fully understand how to read.

The CBC is the one almost every woman gets at some point in time. It's simple, it's cheap, and it's the first thing a doctor orders when you say you're tired. When it comes back normal, that's often where the conversation can end.

So, what is a normal CBC actually worth? What does it tell you about your energy? What does it leave out, and when should you investigate further?

A complete blood count (CBC) is a tally of the cells floating in your blood. Three families of them:

In a national U.S. sample of non-pregnant women aged 12 to 49, the standard anemia cutoff (hemoglobin under 12.0 g/dL, and normally measured in a CBC) caught only 42.9% of the women who were iron deficient.

It misses more iron-deficient women than it finds for one simple reason: a CBC contains no measure of your iron stores.

A CBC measures hemoglobin. Your stored iron is separate. It sits mostly in your liver, in a protein called ferritin. Ferritin is the test that tracks your total body iron, and it's ordered separately from a CBC.

Iron runs out in a specific order. You spend your stores first. Only when they're nearly gone does your body underbuild red blood cells. In iron deficiency without anemia, ferritin is already low, while hemoglobin and red cell size still come out as normal.

Anemia is the very last stage. In women aged 15 to 49, hemoglobin only starts to fall once ferritin drops to about 25 µg/L. Above that, your hemoglobin and red blood cell size typically look normal.

It ensures that we catch the clear cases of anemia. The end of the line.

Low hemoglobin in a menstruating woman is rarely a false alarm. Iron is usually the culprit, accounting for roughly 75% of all anemia.

It doesn’t warn us, however, when we’re well on our way to anemia. And the CBC isn't sorting women by how bad they feel. You can be at the start of iron deficiency, feeling awful, and your CBC will show nothing awry.

Not to mention, it says nothing about things like sleep disorders, depression, and chronic stress, which top the list of reasons for persistent fatigue.

Your CBC numbers are steadier than you'd expect. Across a full menstrual cycle, hemoglobin and red cell size don't meaningfully change. Weekly draws over two cycles put the swing in hemoglobin at about 2%.

They’re also yours. Nine numbers on a CBC are specific enough to tell you apart from 98% of other healthy adults ‼️ and they stay the same for at least 20 years.

The reference ranges on your lab results are built for everyone. In some cases, the top of the range is more than twice the bottom.

Consider those two things together, and you can see how there might be problems. Your result can move a long way from where it normally sits and still land inside the reference range. Nothing gets flagged, but it's not normal for you.

That's why one CBC effectively tells you so little and why your own past results can often be a better comparison than the population’s.

📋 Ask for the CBC numbers themselves. Request a copy of the printed result and add one line about how you felt when you had the blood draw. it could end up telling you what a good (or bad) week looks like on paper.

Here’s what caught my eye this week:

📄 What actually turns up when young women with low iron get scoped: Across 769 American women aged 18 to 44 with iron-deficiency anemia (IDA) and no alarm symptoms who had both endoscopies on the same day, the commonest findings were gastritis (45%), hemorrhoids (32%), hiatal hernia (11%) and H. pylori (10%). However, diagnoses cannot be assumed to be the cause of the anemia, and the study can’t really say whether an endoscopy is worth doing for every of IDA.

📄 Cannabis for sleep does not hold up: A Cochrane review pulled together nine trials and 537 people, nearly three quarters of them women. Against placebo, medical cannabis made little to no meaningful difference to sleep quality, and total sleep time moved by about eight minutes, a result whose error bars run from half an hour worse to half an hour better. Certainty was very low. Given how heavily sleep gummies are marketed to women, the absence of an effect is worth noting.

📄 The largest diet and hip fracture study yet points at protein and zinc: 541,887 postmenopausal women in the Million Women Study, 27,318 hip fractures, nearly 20 years of follow-up, and 99 dietary factors tested at once. Protein and zinc showed the strongest protective associations, alongside vegetables, fibre and carotene, while chips and fizzy drinks went the other way. The authors are careful about what it means: this may be tracking overall diet quality and lifestyle rather than any single nutrient doing the work.

Just sharing here what's new this week. No affiliates, no sponsorships, no freebies. A mention here isn't a recommendation.