Biomarkers

What Causes Dizziness, and What Blood Tests Can Check

Most dizziness is not diagnosed by bloodwork. A specific short list of contributors can be checked, and a few presentations are emergencies. Here is how to tell them apart, the marker to start with for each blood-testable cause, and where each one stops.

Medically Reviewed By: Rhonda Collins, FNP-C | September 17, 2026 | 13 min read

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Most dizziness is not diagnosed by a blood test. A large share of it comes from the balance organs of the inner ear, and another common share from how your circulation responds when you stand up. Neither shows up in bloodwork. What blood testing can do is check a short, specific list of body-wide contributors: low iron stores, low or unstable blood sugar, thyroid dysfunction, low sodium and other electrolyte disturbances, and vitamin B12 deficiency. And a small number of dizziness presentations are emergencies that need care now rather than a lab order.

This page separates those three groups, names the marker to start with for each blood-testable contributor, and is straight about where a single marker stops being able to tell you anything.

When dizziness is an emergency, not a lab question

Some dizziness needs immediate medical care rather than a blood test. Get emergency help if sudden or severe dizziness arrives with any of the following:

• chest pain, shortness of breath, or a racing or irregular heartbeat
• fainting, or nearly fainting
• slurred speech, or trouble understanding speech
• weakness or numbness on one side of the face or body
• double vision, loss of vision, or new trouble walking or standing
• a severe headache unlike any you usually get

Notice that every item on that list is something happening alongside the dizziness. That is deliberate. In a population-based study of people over 44 who came to an emergency department with dizziness, vertigo, or imbalance, a stroke or transient ischemic attack was found in 3.2 percent, and in only 0.7 percent of those whose dizziness came with no other neurological symptom or sign [1]. Dizziness on its own is a strong predictor of a cause that is not a stroke. Dizziness with company is the combination that needs urgent attention, and what sorts it out in that setting is a bedside neurological examination, not bloodwork [2].

Fainting is its own category. A genuine loss of consciousness, particularly one that happens during exertion or alongside chest pain, warrants prompt evaluation rather than self-directed testing [3].

Common causes of dizziness sit in the inner ear, where blood work cannot see them

A large share of dizziness is vestibular, meaning it comes from the balance organs of the inner ear. In a nationally representative survey of German adults, vestibular vertigo affected 4.9 percent of people over a 12-month period, and 7.4 percent at some point in their lives [4]. Benign paroxysmal positional vertigo (BPPV), in which brief spinning is set off by rolling over in bed, lying down, or tipping the head back, accounted for 8 percent of everyone in that survey with moderate or severe dizziness, with a lifetime prevalence of 2.4 percent [5]. BPPV is identified by a positioning maneuver performed at the bedside, and the guideline for it specifically discourages unnecessary ancillary testing [6].

A second common pattern is positional in a different sense. If the lightheadedness arrives only in the seconds after you stand up, that points to how your blood pressure responds to standing, which is measured with a blood pressure cuff before and after standing rather than with a blood test [7].

Two consequences follow, and they matter for how you read any result:

• Normal bloodwork does not mean nothing is wrong. The most common causes of dizziness would produce a completely normal panel.
• An abnormal marker does not prove it caused the dizziness. It identifies a contributor worth correcting, which is a different and weaker claim.

What blood work can and cannot check for dizziness

Blood testing does not diagnose dizziness. What it does is check a specific set of body-wide conditions that can cause lightheadedness on their own, or make an inner-ear problem feel worse than it otherwise would. It narrows the list rather than closing it.

Blood work can check iron stores, blood glucose, thyroid function, sodium and the other electrolytes, and vitamin B12.

Blood work cannot check the inner ear, your blood pressure response to standing, migraine, anxiety, or the side effects of a medicine you started recently. Those are answered by history, examination, and a medication review.

The blood-testable contributors, and the marker to start with for each

Each of the five below is a real, checkable contributor to dizziness and lightheadedness, and each has one marker that is the sensible place to start.

One caveat applies to all five, and it matters before you order anything. A single marker is a screen, not a verdict. A normal result narrows the list, but for several of these a normal result does not by itself rule the cause out, either because the marker can read normal while the problem is present or because a single scheduled draw cannot capture something that comes and goes. Each section below says where its own marker stops.

Iron deficiency: check ferritin

Iron deficiency is the most common nutritional deficiency worldwide. When it progresses to anemia it reduces the blood’s oxygen-carrying capacity, and lightheadedness sits alongside fatigue, weakness, and breathlessness among its recognized symptoms [8][9].

Ferritin is the marker to order, because it reflects iron stores and falls before hemoglobin does. That means ferritin identifies iron depletion at a stage when a standard blood count still looks normal [8]. If your dizziness comes with tiredness, breathlessness on stairs, or unusually heavy periods, this is the first thing to check.

Where ferritin stops: it is an inflammatory marker as well as an iron marker, so inflammation, infection, and some liver and chronic conditions can hold it normal or push it high while iron stores are genuinely low. Absolute iron deficiency is straightforward to identify on ferritin alone unless it is masked that way [8]. So a normal ferritin alongside an inflammatory condition is not a clearance, and the iron picture is finished with the wider iron studies rather than this one number.

Start with a ferritin blood test. For what the marker measures, see ferritin; for the fuller iron workup, including what gets added when ferritin is not conclusive, see our anemia test guide.

Blood sugar: check glucose

Low blood glucose causes shakiness, sweating, hunger, and dizziness or lightheadedness, and those symptoms typically resolve once glucose is restored [10]. The risk is concentrated in people taking insulin or certain other diabetes medicines.

Where a glucose test stops, and this is the important one on this page: a lab draw measures your blood sugar at the moment the needle goes in. If your dizziness comes and goes with meals, long gaps without eating, or exercise, a scheduled draw taken when you feel fine can easily come back normal while the episodes continue. Low blood sugar is only established when a low glucose is measured during an episode and the symptoms resolve as glucose comes back up, which is the standard the Endocrine Society sets for investigating it at all [11]. Arranging that measurement is a conversation with your doctor, not a test you can schedule around a symptom that has already passed.

What a standalone glucose blood test is good for is the other question: it is a snapshot of your blood sugar and a first-line screen for diabetes and prediabetes, which is worth knowing if your dizziness comes with thirst, frequent urination, or unexplained weight change. Order it for that, not as a way to rule out episodic lows. For what the marker measures, see glucose.

Thyroid function: check TSH

Thyroid hormone sets heart rate, cardiac output, and the tone of your blood vessels, so both an underactive and an overactive thyroid change how your circulation behaves [12]. That is one plausible route to lightheadedness, and it is worth checking when dizziness comes packaged with other thyroid symptoms: changes in weight, temperature tolerance, heart rate, energy, or menstrual pattern.

TSH is the first-line test for thyroid function in both directions, which is what makes it the efficient single marker to open with [13][14]. Where it stops: TSH is a screen, so an abnormal result is the start of a thyroid workup rather than a diagnosis. Confirming what is actually going on, and how to treat it, takes follow-up testing your doctor orders on the strength of that first result [13][14].

Start with a thyroid-stimulating hormone (TSH) blood test. For what the marker measures, see thyroid-stimulating hormone.

Sodium and electrolytes: check an electrolyte panel

Sodium is the electrolyte with the clearest link to feeling unsteady. Mild, long-standing low sodium, the kind that produces no obvious symptoms and is usually called asymptomatic, has been associated with unsteadiness, slower attention, and falls [15]. That finding has limits: it comes from a case-control study of mostly older patients presenting to a medical emergency department, so it is an association in that population rather than proof of cause in everyone. It is a strong enough signal that low sodium is worth checking when dizziness is unexplained.

Low sodium has several routes: some medicines, including thiazide diuretics and certain antidepressants; drinking large volumes of plain water during prolonged exercise; and a number of medical conditions [16]. Separately, losing fluid through vomiting, diarrhea, or heat reduces blood volume, which is a common reason people feel lightheaded on standing.

Where this one stops: sodium is measured directly, so the number is what it is on the day. But it is still a single point in time, so a panel drawn on an ordinary day says little about what your sodium does during a hot week, a stomach bug, or a long race.

Start with an electrolyte panel. For what sodium itself measures, see sodium, and for how the other electrolytes present, see our electrolyte imbalance symptoms guide.

Vitamin B12: check vitamin B12

Vitamin B12 deficiency can cause anemia, and separately it can cause neurological problems including numbness and tingling in the hands and feet, and difficulty with balance and walking [17][18]. The balance element is what makes it relevant here: unsteadiness from B12 deficiency is a different mechanism from the spinning of an inner-ear problem, and it can develop before the anemia does [17].

The risk is higher in older adults, in people taking metformin or acid-reducing medicines long-term, and in people eating little or no animal food [17][18].

Where serum B12 stops: there is no single gold-standard test for B12 status. Serum B12 is the first-line test, but results in the borderline band are genuinely ambiguous, and clarifying them takes a second-line methylmalonic acid measurement [19]. So a clearly low result is informative, and a borderline one is a reason to keep going rather than a clearance.

Start with a vitamin B12 blood test. For what the marker measures, see vitamin B12.

If you would rather start with one broad panel

The five tests above are the efficient route when you have a lead. If you do not, and your dizziness comes alongside other symptoms you have not been able to place, one broad first pass can be more useful than guessing at a single marker.

The Mito Core Panel covers all five of the markers on this page, ferritin, glucose, TSH, sodium, and vitamin B12, in a single draw, along with the rest of a general health picture. As with any Mito result, a clinician reviews it before your analysis is finalized, which matters more when you are looking at a wide panel with no specific question in mind.

That is a reasonable starting point when you have no lead at all. It is not the answer to any one of the contributors above, and the same limits apply: a wide panel is a wider screen, not a wider set of verdicts. If your symptoms already point at iron, or thyroid, or electrolytes, start with that single marker instead.

When to see a clinician about dizziness

Bloodwork sits alongside a clinical evaluation of dizziness, not in place of one. Book an appointment if any of these apply:

• the dizziness is persistent, keeps coming back, or has no explanation you are confident in
• it started after you began a new medicine, or changed a dose
• it comes with hearing changes or ringing in one ear
• you have fallen, or you are avoiding activities because you are afraid you will
• your bloodwork came back normal and the dizziness has not gone away

A clinician can do the two things a blood panel cannot: examine the balance system directly, and measure how your blood pressure responds when you stand.

Related reading

• Always Tired? Blood Tests That Can Reveal Hidden Causes of Fatigue
• Can Anemia Cause Body Aches? Understanding the Link to Muscle and Joint Pain

Resources

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