Seizures in adults come from two broad situations. Some are provoked by a temporary insult such as severe sleep loss, alcohol withdrawal, low blood sodium, very low blood sugar or some medicines. Others reflect epilepsy, a lasting tendency of the brain to produce seizures. Blood tests can flag the reversible causes, and a clinician interprets them.
This page is educational and is not medical advice.
Most adult seizures follow something temporary rather than a lifelong brain condition. A seizure is a burst of abnormal, synchronised electrical activity in the brain, so anything that lowers the threshold for that burst can tip a brain into one. That is why a clinician will ask about the 48 hours before the event in unusual detail. Evaluation of a first seizure in an adult is organised around separating a provoked seizure, which follows an identifiable insult, from an unprovoked one, which raises the question of epilepsy 1.
The ordinary precipitants come first because they are the most common.
Head injury, central nervous system infection, stroke and structural lesions account for a real share of adult seizures as well, which is why brain imaging usually joins the blood work after a first event 1.
None of this is self-diagnosis territory. The point of knowing the list is to give the clinician who assesses you a clean, honest account of the days before the seizure.
Blood tests after a seizure look for provoked and reversible causes rather than confirming or excluding epilepsy 1. Four routine markers do most of that work. Research suggests that metabolic disturbances, including abnormalities of sodium, glucose, calcium and magnesium, belong on the list of causes considered when seizures are assessed 5.
| Marker | Why it is linked to this symptom | What a result can and cannot tell you |
|---|---|---|
| Sodium | Sodium sets the osmotic balance between blood and brain tissue. When it falls, water shifts into brain cells and neuronal excitability changes. | A low value points to one reversible reason worth discussing with a clinician promptly. A single reading cannot show how fast sodium fell, and speed matters as much as the number. |
| Fasting glucose | The brain depends on a continuous glucose supply and has almost no reserve of its own. Both very low and very high glucose disturb brain function. | A low fasting value is worth prompt discussion. A normal fasting value says nothing about overnight dips or post-meal swings, which need different testing. |
| Calcium | Calcium stabilises nerve cell membranes, so low calcium raises excitability across the nervous system. | Total calcium is influenced by albumin, so a borderline result may need albumin correction or an ionised calcium. A normal calcium does not rule out other electrolyte problems. |
| Magnesium | Magnesium regulates the receptors and channels that control how readily neurons fire, and it works alongside calcium and potassium. | Serum magnesium reflects only a small fraction of total body stores, so a normal serum value does not prove tissue stores are adequate. |
Typical adult reference ranges for these markers are shown below.
| Marker | Typical lab reference range |
|---|---|
| Sodium | 135 to 145 mmol/L |
| Fasting glucose | 70 to 99 mg/dL |
| Calcium (total) | 8.6 to 10.2 mg/dL |
| Magnesium | 1.7 to 2.2 mg/dL |
These are typical lab reference ranges and they vary by laboratory, age and sex. Read your own report against the range printed on it, and discuss anything outside that range with a clinician.
Yes, low blood sodium is one of the best recognised reversible reasons a seizure happens, and it is checked early for exactly that reason. Sodium is the main solute holding water in the bloodstream. When the concentration falls, water moves down the osmotic gradient into cells, including brain cells, and swelling in a fixed skull changes how neurons behave. A fall that happens over hours is more disruptive than the same value reached slowly over weeks, because the brain has had no time to adapt.
Studies of first seizure assessment in adults include serum electrolytes and glucose in the initial laboratory work precisely because these findings change what happens next 1. Low sodium also appears among the metabolic disturbances considered when seizures are evaluated 5.
Plenty of things move sodium other than a seizure disorder. Large sweat losses replaced with plain water during long endurance efforts, vomiting and diarrhoea, drinking far more fluid than the kidneys can clear, some medicines, and heart, liver, kidney or hormonal conditions all shift it. That is the honest limit of the test. A low result flags a situation worth sorting out, it does not name the reason by itself. You can read more about what the test measures on the Sodium marker page.
Yes, glucose that drops low enough can provoke a seizure, and glucose that runs very high can do it through a different route. The brain burns glucose almost exclusively and stores very little, so a steep fall starves the tissue that is hardest to run on anything else. Confusion, sweating and tremor usually come first, but a seizure can be the presenting event, particularly overnight or in people whose warning symptoms have faded over time.
Glucose abnormalities sit alongside electrolyte disturbances in the metabolic causes considered during seizure assessment 5. Adult epilepsy reviews separate seizures provoked by metabolic and toxic causes from epilepsy itself, because the two lead down different paths 4.
A fasting glucose is a snapshot taken at the calmest point of the day. It will not capture an overnight dip, a reactive drop a few hours after a large meal, or the swings that follow heavy alcohol intake on an empty stomach. The Fasting Glucose page explains what the single value does and does not represent.
Yes, calcium stabilises nerve and muscle cell membranes, and when the ionised fraction falls the whole nervous system becomes more excitable. Tingling around the mouth and fingers, muscle cramps and spasm usually appear before anything more dramatic, but a seizure is one of the ways significantly low calcium can present. Low calcium appears among the metabolic disturbances reviewed as causes of seizures 5.
The measurement has a quirk worth knowing. Most panels report total calcium, which includes the portion bound to albumin, so a low albumin drags the total down even when the biologically active ionised calcium is fine. A borderline total calcium on its own therefore means less than it looks like, and a clinician may correct for albumin or order an ionised calcium instead.
Other things change calcium too. Parathyroid function, vitamin D status, kidney function, gut absorption, prior neck surgery and magnesium status all feed into it. A normal calcium is reassuring for that one question and silent on the rest, which is the general rule for every marker on this page. See the Calcium page for what the result covers.
Magnesium sits one layer behind calcium and is easy to overlook. It regulates several of the channels and receptors that govern how readily a neuron fires, and low magnesium is one of the electrolyte disturbances considered in the metabolic causes of seizures. Low magnesium also tends to pull calcium and potassium down with it, so a single low magnesium often sits in the middle of a wider picture rather than alone.
The measurement has a real limitation. Serum magnesium reflects only a small share of total body magnesium, most of which sits in bone and inside cells, so a serum value inside the typical range does not prove stores are replete. It is still worth measuring, because a clearly low serum result is informative and easy to act on under clinical supervision.
What else moves it. Sustained heavy alcohol intake, poor dietary intake, diarrhoea and other gut losses, malabsorption, kidney handling of magnesium and some medicines all shift the number. Ask your prescriber about anything you take before assuming a cause. The Magnesium page sets out what the serum test represents.
A completely normal blood panel does not rule out a serious reason for a seizure, and that is the single most important limitation on this page. Blood work is built to catch the reversible metabolic causes. It is not built to detect the structural and electrical ones.
Structural causes sit outside the reach of a blood draw. Prior stroke, head injury, scarring, vascular malformations and tumours are questions for imaging, not chemistry. Electrical patterns are a separate question again. After a first seizure, EEG and brain imaging are used to assess the risk of a further seizure, which laboratory testing cannot estimate 6. The evaluation of a first adult seizure is therefore a combination of history, examination, blood tests and, in most cases, imaging 1.
Timing is the other blind spot. Electrolytes and glucose move. A sodium or glucose value drawn days after an event may have normalised completely, so the result reflects today rather than the moment the seizure happened. The same applies to sleep, alcohol and stress, none of which leaves a fingerprint on a standard panel. A careful account of the hours beforehand, ideally from someone who witnessed the event, frequently carries more weight than the chemistry.
Finally, epilepsy itself has no blood marker. A diagnosis is a clinical judgement made by a neurologist from the pattern of events and the supporting tests, never from a lab value.
Some situations need emergency services rather than an appointment. Call 911 for a seizure lasting longer than 5 minutes, for repeated seizures without full recovery in between, for a first-ever seizure, for a seizure in water, for a seizure with a head injury, and when breathing does not return to normal or the person stays unresponsive afterwards. Prolonged and repeated seizures are handled as a medical emergency, and finding a provoking cause is part of that early assessment 7.
Arrange prompt, same-week medical review for any seizure-like event that has already ended, for new blackouts or episodes of lost awareness, for a seizure during pregnancy, for one that follows a recent head injury, for one accompanied by fever, severe headache, neck stiffness or new weakness, and for an episode that happens while cutting back on alcohol after sustained heavy drinking. Anyone who has had a seizure should also ask a clinician about driving and about safety around water, heights, machinery and cooking before resuming normal routines.
A lab value outside the standard range after an event is not something to shrug off, and it is not something to interpret alone. It is worth discussing with a clinician promptly, who will look at it alongside your history rather than in isolation.
If you are having thoughts of self-harm, call or text 988 (US) or your local emergency number now.
Sodium, fasting glucose, calcium and magnesium are routine chemistry markers, and all four are measured in the FitScript Essential panel. Membership covers 150+ biomarkers tested per year, so these values can be tracked over time rather than read once from a single draw, which matters for markers that move with hydration, training load and intake.
Atlas, FitScript's AI health advisor, explains what each result means in plain language and shows how your values sit against the standard reference range. That interpretation is education, not a diagnosis. Any next step, including further testing, imaging, referral or any treatment decision, belongs to a licensed provider who has reviewed you.
If you have had a seizure or a seizure-like event, book a clinical assessment first. Testing supports that assessment, it does not substitute for it.
Seizures happen when brain cells fire in an abnormal, synchronised burst. In adults, common reasons include severe sleep loss, alcohol withdrawal after heavy drinking, low blood sodium, very low blood sugar and some medicines. Epilepsy is the other broad category. A clinician works out which fits using your history, an examination and blood tests.
Repeated seizures usually have a different explanation from a single provoked one. Recurring unprovoked seizures point towards epilepsy, while recurring provoked ones point to something that keeps happening, such as ongoing alcohol withdrawal, persistently low sodium or unstable blood sugar. A neurologist decides which pattern fits after assessment and testing.
There is rarely one single cause. A seizure needs a brain that is temporarily more excitable than usual, and that state can come from electrolyte shifts, low glucose, sleep loss, alcohol, head injury, stroke, infection or an underlying epilepsy. Blood work narrows the list, and a clinician interprets the whole picture.
Stress is one of the triggers people report most often, though it usually arrives alongside poor sleep, skipped meals and more alcohol. On its own it rarely explains a first seizure, so it does not replace a proper assessment. Tell your clinician about sleep, workload and alcohol, because those details change what gets checked.
Yes. A standard electrolyte panel measures sodium, so a low value will appear on the report. What one reading cannot show is how quickly sodium fell, and speed often matters more than the number itself. A low or rapidly changing result is worth discussing with a clinician promptly.
No. A single seizure with a clear provoking cause is often a one-off, and many people never have another. Epilepsy describes a lasting tendency towards unprovoked seizures, and a neurologist usually needs more than one event, or supporting tests such as an EEG and brain imaging, before applying that term.
Sodium, glucose, calcium and magnesium are the routine ones, often alongside kidney function, liver markers and a blood count. They look for reversible reasons rather than confirming epilepsy. Imaging and an EEG answer different questions, and the clinician who assessed the event decides what is needed and in what order.
Both can lower the threshold at which the brain fires abnormally, especially when they stack with alcohol, heavy training or illness. Skipped meals matter most in people whose blood sugar already runs low. Keeping a simple log of sleep, meals and alcohol gives your clinician something concrete to work from.