Epilepsy in dogs is diagnosed through a process of elimination rather than a single definitive test. There is no blood marker or scan that confirms epilepsy on its own. Instead, your vet works through a structured series of steps to rule out other causes of seizures, such as toxin exposure, organ disease, or brain tumors, before arriving at an epilepsy diagnosis. The international standard uses a tiered system, with each level offering greater diagnostic confidence.
What Your Vet Needs From You First
The diagnostic process starts before any lab work, with your observations at home. Because vets rarely witness a seizure firsthand, what you describe is critical. You’ll be asked about your dog’s age when seizures began, how many seizures have occurred, and how far apart they were. Two or more unprovoked seizures at least 24 hours apart is the minimum threshold that points toward epilepsy rather than a one-time event.
Many veterinary clinics will ask you to keep a seizure diary going forward. The key details to record include how long each seizure lasted, what your dog was doing immediately before it started (sleeping, running, resting), any unusual behavior in the minutes leading up to the seizure, and what happened afterward. That recovery period, called the postictal phase, is particularly telling. Dogs with epilepsy commonly show disorientation, compulsive walking, unsteadiness, or temporary blindness after a seizure. These signs can last anywhere from minutes to several days and help distinguish true seizures from fainting episodes, which typically have a much quicker recovery.
Tier I: Blood Work and Physical Exam
The first level of diagnosis involves a thorough physical and neurological exam between seizures, along with baseline blood tests and a urinalysis. Your vet is looking for metabolic or toxic causes that could trigger seizures in an otherwise normal brain. These are called reactive seizures, and they’re reversible once the underlying problem is treated.
The blood work screens for conditions like liver disease, thyroid disorders, electrolyte imbalances, and infections. In one study of dogs with reactive seizures, the causes included hepatic encephalopathy (a buildup of toxins due to liver failure), hypothyroidism, uterine infection, and cardiopulmonary failure. A complete blood cell count and serum biochemical profile catch most of these problems. If everything comes back normal, your dog’s neurological exam looks clean, and seizures started between six months and six years of age, your vet has reached the first tier of diagnostic confidence for idiopathic epilepsy.
That age window matters. Dogs with idiopathic epilepsy typically begin seizing between 6 months and 6 years old, with a median onset around 2.5 years. If seizures start outside that range, the international veterinary epilepsy task force recommends against labeling it idiopathic epilepsy, even if no cause is found. Dogs with onset after age six are classified as having epilepsy of unknown cause, and further testing is strongly encouraged.
Tier II: MRI and Spinal Fluid Analysis
For greater diagnostic certainty, your vet may recommend an MRI of the brain and analysis of cerebrospinal fluid (the liquid surrounding the brain and spinal cord). These tests look for structural problems like tumors, inflammation, infections, or malformations that could be causing the seizures. If both come back clean, and the Tier I criteria are already met, your dog reaches the second tier of confidence for an idiopathic epilepsy diagnosis.
Not every dog needs an MRI right away. The international guidelines specifically recommend brain imaging and spinal fluid testing when:
- Seizures started before 6 months or after 6 years of age, since these dogs are more likely to have a structural or metabolic cause
- Neurological abnormalities are present between seizures, such as head tilting, circling, vision changes, or coordination problems
- The first seizure episode was prolonged or came in clusters, which raises the likelihood of an underlying brain problem
- Medication isn’t controlling the seizures, particularly if a single anti-seizure drug has been increased to its maximum tolerable dose without adequate results
MRI requires general anesthesia, and the cost can be significant, so understanding these specific triggers helps you and your vet decide when the added information is worth pursuing. The spinal fluid is typically collected during the same anesthesia session, since the dog is already under.
Tier III: Brainwave Testing
The highest level of diagnostic confidence adds electroencephalography (EEG), which records electrical activity in the brain. In human medicine, EEG is a cornerstone of epilepsy diagnosis. In veterinary medicine, the reality is quite different.
A global survey of veterinary neurologists found that while 75% had performed an EEG on a dog at some point, only 44% were still using the technology. Among those who did, the majority used it only once a year or less. The reasons are practical: lack of specialized equipment, limited training, high cost, and questions about how much useful information it provides in dogs compared to humans. The number of electrodes used varies widely between clinics, ranging from 6 to 32, and no standardized, validated electrode placement system exists for dogs. Without that standardization, it’s difficult to pinpoint exactly which part of the brain is generating abnormal signals.
Dog-specific challenges make EEG harder to perform reliably. Skin elasticity and mobility differ across breeds, and simply changing a dog’s position can shift electrode placement. Some researchers have explored using MRI-guided electrode positioning for better accuracy, but requiring an expensive imaging session just to set up a cheaper test limits its practicality. For most dog owners, Tier III testing remains uncommon and is largely confined to specialty referral hospitals or research settings.
Why Age and Breed Both Matter
Your dog’s age at seizure onset is one of the strongest clues your vet uses to narrow down the diagnosis. The 6-month to 6-year window is the hallmark of idiopathic epilepsy, which is believed to have a genetic basis in many cases. Certain breeds have a well-documented predisposition, including Labrador Retrievers, German Shepherds, Golden Retrievers, Beagles, Border Collies, Australian Shepherds, Irish Setters, and Belgian Shepherds, among others. Having a predisposed breed strengthens the case for a genetic component, though epilepsy can occur in any dog.
When seizures begin in a very young puppy (under 6 months), vets are more concerned about developmental brain abnormalities, infections, or congenital liver shunts that allow toxins to bypass the liver and reach the brain. When seizures first appear in a senior dog, brain tumors and degenerative conditions move to the top of the list. In both scenarios, the diagnostic pathway shifts toward earlier imaging rather than waiting to see if blood work alone provides the answer.
What the Diagnosis Looks Like in Practice
For many dog owners, the diagnostic process unfolds over weeks or months rather than in a single visit. Your vet will likely start with blood work and a neurological exam at the first appointment after a seizure. If results are normal and your dog falls within the typical age range, you may receive a working diagnosis of probable idiopathic epilepsy and begin discussing whether treatment is needed based on seizure frequency.
If seizures become more frequent, don’t respond to medication, or if your dog develops new neurological symptoms between episodes, your vet will recommend moving up to Tier II testing with an MRI and spinal fluid analysis. This step usually involves a referral to a veterinary neurologist. The goal at every stage is the same: make sure nothing treatable is being missed before settling on a diagnosis of epilepsy that will require lifelong management.
Keep your seizure diary updated and bring it to every appointment. The pattern of your dog’s seizures, including how often they happen, how long they last, and whether they’re getting worse, is data your vet can’t get from any scan or blood test.