Blood tests for brain fog: B12, iron, thyroid, blood sugar, sodium and calcium

The blood tests most worth checking for brain fog are vitamin B12, ferritin (stored iron), thyroid hormones, blood sugar, sodium and calcium, because each can affect how clearly you think when it's off.

Brain fog isn't a diagnosis, and bloodwork's job is to find the treatable causes behind it. Numia Health, a physician-ordered, at-home blood testing service in Greater Vancouver, measures all six in one Fatigue Panel draw.

If brain fog comes on suddenly with trouble speaking or a drooping face or arm, those are stroke signs: call 9-1-1. If it's new or getting worse, see a clinician first.

Which blood tests are worth checking for brain fog?

Your doctor can add a CBC (complete blood count), which checks for anemia. Already had "normal" bloodwork? See what to do next.

Why can B12 or iron matter with a normal blood count?

Folic acid can mask the anemia that B12 deficiency usually causes, so BC's B12 guideline warns the deficiency "may present with exclusively neurologic features." Metformin and acid-reflux drugs raise the risk. Numia's Fatigue and Basic Nutrients panels both report B12 and folate together.

In a 16-week trial of 149 young women, those low on iron but not anemic scored between the iron-sufficient and anemic groups on thinking tasks. A rise in ferritin was linked to a 5- to 7-fold improvement in performance (Murray-Kolb & Beard, 2007). Numia's Fatigue Panel reads ferritin alongside iron, TIBC and saturation. Low ferritin is also linked to restless legs.

Why is a baseline worth having?

Here's the catch: some changes build quietly. In a US national survey, 84% of adults with prediabetes (blood sugar above normal but below diabetes) didn't know they had it (Wang et al., 2025). A baseline shows where you stand now; a retest shows which way you're heading. That's easier when every result sits in one place, like the Numia app.

Where does Numia fit?

Numia Health keeps every step in one place. The usual route is an appointment, a requisition, a lab visit, a wait, then another appointment for results. With Numia, a licensed Canadian physician approves your requisition online in about 3 minutes, and a BC-licensed clinician comes to your home for a 10-minute morning draw. The Fatigue Panel measures 22 biomarkers across five systems and needs an 8–12 hour fast.

Results arrive in plain English in the Numia app in 7 days, and the Numia Companion, an AI that has read them, answers questions. Out-of-range results are physician-reviewed with recommended next steps, and an optional wellness consultation is available. Numia is an HSA-eligible service.

Frequently asked questions

What blood work is done for brain fog?

Usually B12, ferritin, thyroid, blood sugar, sodium and calcium, plus a CBC. Numia's Fatigue Panel includes everything but the CBC in one draw.

What lab tests are ordered for cognitive impairment and fatigue?

Canadian dementia guidance recommends a CBC, TSH, calcium, electrolytes and fasting glucose, plus B12 for older adults. Numia's Fatigue Panel includes all of these except the CBC.

What if my brain fog blood tests come back in range?

That rules out several treatable causes. Sleep apnea, perimenopause, long COVID, mood and some medications can also cloud thinking; a clinician can help. Don't stop a prescribed medication without your prescriber.