How Often Should You Get Blood Work Done?
This one came from a patient of mine. She has done three sets of blood work over a year, found her stride, and things are going well. Her question was simple: now that things are stable, how often should I get my blood checked? I get it often enough that it is worth answering properly.
How often should you get blood work done?
Twice a year, if you are using blood work to decide what you eat and what you take. The medical profession has settled on an annual physical, which means blood drawn once a year, and for the job that system is built for, catching disease, once a year is fine. Disease moves slowly. A doctor is not going to pick up a change related to a disease process in six months. But your supplement needs and your dietary needs can shift dramatically in three to six months, and if that is what your blood work is for, a year is too long to go without looking.
I would double that. Once every six months, twice a year, when everything is going well.
Why isn’t once a year enough?
Because you are taking things based on last year’s numbers. Say your blood work shows you are low in vitamin B12, so you start taking it. B12 is something that can replenish fairly quickly. Six months on, you have no idea whether you still need that dose, and under the once-a-year model you will keep taking it for another six months to find out. The same goes for vitamin D, and for iron, and for most of the things people take because a lab result told them to.
There is a practical side to this too. If you retest at six months, you can plan your supplement purchases over a six-month period instead of a twelve-month one. You stop paying for a year of something you needed for four months, and you catch the thing you have started to run short of before it becomes a symptom.
What are you looking for at a six-month check?
Patterns, more than any single number. One result is a snapshot. Two, six months apart, are a direction, and direction is what tells you whether what you are doing is working. The things I am watching for most people:
- Insulin resistance. If you are fine-tuning it, fasting insulin moves within weeks of a change in diet, and A1c reflects roughly the previous three months, so six months is long enough to see both respond.
- Inflammation. If you have brought your inflammatory markers down, you want to know whether anything has crept back.
- Antibodies, if you have a history of an autoimmune condition. If something triggered a flare, the antibodies rise, and twice a year is often enough to catch a dramatic change while it is still a number rather than a symptom.
- The nutrients you are supplementing: B12, vitamin D, magnesium, and ferritin if iron was the problem. These are the ones that decide whether the bottle stays on the shelf.
Can blood work measure cortisol?
Yes, but a blood draw catches one moment of a hormone that runs on a 24-hour rhythm, so it needs reading with that in mind. Cortisol should be highest first thing in the morning. If the lab’s reference range is 6 to 19, I want to see a morning sample up around 15 to 20. Scraping along the bottom of the range at seven in the morning is a finding in itself. If what you want to know is the rhythm, there is a saliva test that samples four times, on waking, at noon, at four in the afternoon and at bedtime, and maps the whole curve. I go through what high cortisol looks like, and how to test it properly, in the signs of high cortisol in women.
Cortisol and inflammation are also tied together more closely than people expect, through belly fat. The fat around your organs carries an abundance of cortisol receptors and can switch inactive cortisone back into active cortisol, so a normal cortisol level gets amplified in that tissue, and the same fat releases the inflammatory signals that show up as C-reactive protein. That is why a rising CRP and a stubborn waistline tend to arrive together, and why I treat them as one problem. More on that in how to lose visceral fat.
When is more often than twice a year worth it?
- After you change a dose. If you have gone from 2,000 to 5,000 units of vitamin D, or started iron, a recheck at around three months tells you whether the new dose is doing what you wanted, before you have spent a year on it.
- After an autoimmune flare, or anything that might have triggered one, so you can see the antibodies and the inflammatory markers settle back.
- When you are actively fine-tuning insulin resistance and want to see whether a change in diet or walking has moved the needle. A1c covers three months, so three months is the shortest useful gap for that one.
When is once a year fine?
When nothing is being adjusted. If your numbers have been stable for a couple of years, you are not changing any supplement, your diet is settled and you feel well, the annual physical does its job and I would not push you to double it. The six-month rhythm is for people who are using their blood work to make decisions, which, if you are reading this, is probably you.
So: twice a year while you are working on something, three months after any change in dose, and once a year once it is all boring. Boring, on blood work, is the goal.
