Introduction: When Should You Seek Diagnostic Testing?

Anyone experiencing persistent or worsening symptoms that affect brain function should seek medical attention promptly. Glioblastoma symptoms often come on quickly and can be mistaken for other conditions, which is why early evaluation is so important.^[1] The growing tumor puts pressure on healthy brain tissue, and this pressure causes many of the symptoms that bring people to the doctor.^[2]

You should consider seeing a healthcare provider if you experience persistent headaches that are particularly severe in the morning, as this is one of the most common early warning signs.^[1] Other symptoms that warrant medical evaluation include sudden or gradual changes in vision, such as blurred or double vision, unexplained nausea and vomiting, memory problems, personality changes, difficulty speaking, or new-onset seizures, especially in adults who have never had seizures before.^[1][2] Some people also experience weakness on one side of the body, problems with balance or coordination, or changes in sensation like numbness or tingling.^[2]

Because glioblastoma symptoms can resemble those of a stroke or other serious conditions, it is crucial to get a full medical workup from your doctor if you or a loved one experience these warning signs.^[8] The symptoms tend to worsen rapidly as the tumor grows, and in some cases can progress to unconsciousness if left untreated.^[4] Early diagnosis can make a significant difference in planning appropriate care and starting treatment as soon as possible.

Classic Diagnostic Methods for Identifying Glioblastoma

The diagnostic process for glioblastoma typically begins with a careful evaluation by a healthcare provider. This starts with a neurological examination, which is a physical exam that checks various functions controlled by the brain. During this exam, the doctor will test your vision, hearing, balance, coordination, strength, and reflexes.^[10] Problems in one or more of these areas can provide important clues about which part of the brain the tumor is affecting and help guide further testing.^[10]

Imaging Tests

If a brain tumor is suspected after the neurological exam, imaging tests are the next step. These tests create detailed pictures of the inside of the brain, allowing doctors to see the exact location and size of any abnormal growths.^[10]

Magnetic Resonance Imaging (MRI) is the most important and commonly used imaging test for diagnosing glioblastoma.^[6][10] An MRI uses powerful magnets and radio waves to create very detailed images of the brain’s soft tissues. Usually, images are taken both before and after the injection of a contrast dye into a vein. The contrast helps make the tumor more visible on the images. Glioblastomas typically show strong contrast enhancement and often have areas of dead tissue (called necrosis) in the center of the tumor.^[6] The brightness and pattern on the MRI can give doctors important information about the type and aggressiveness of the tumor.

In addition to standard MRI, doctors may use specialized imaging techniques to learn more about the tumor. Magnetic Resonance Spectroscopy (MRS) is a tool based on MRI technology that provides information about the chemical composition of the tumor.^[6] Different chemicals are present in different amounts in normal brain tissue compared to tumor tissue. For example, a chemical called choline is more abundant in tumors, while N-acetylaspartate (NAA) is more common in healthy brain. This technique works like a non-invasive tissue sampling, although it is not as definitive as an actual biopsy.^[6]

Computed Tomography (CT) scans may also be used to look for brain tumors, especially in emergency situations when quick imaging is needed.^[6][10] A CT scan uses X-rays and a computer to create three-dimensional images of the body. While not as detailed as MRI for viewing brain tissue, CT scans are faster and can be useful in certain situations.

Other advanced imaging tests may include Positron Emission Tomography (PET) scans, which can show how active the tumor cells are by measuring their metabolism.^[10] A special type called 18F-DOPA PET imaging can identify the most aggressive, metabolically active regions of the glioblastoma, which helps doctors plan treatment more precisely.^[13]

Biopsy: Confirming the Diagnosis

Imaging tests can suggest glioblastoma, but the only way to confirm the diagnosis is through a biopsy. A biopsy is a procedure in which a sample of the tumor tissue is removed and sent to a laboratory for examination under a microscope.^[10][18] This can be done with a needle before surgery or during surgery to remove the tumor.

A specialized doctor called a neuropathologist examines the tissue sample to determine whether the cells are cancerous and, if so, what type of brain tumor it is.^[8] The pathologist looks at the appearance of the cells and the tissue structure. For glioblastoma, they need to see either the formation of new blood vessels within the tumor (called microvascular proliferation) or areas of dead cells (necrosis).^[15]

Molecular and Genetic Testing

Modern diagnosis of glioblastoma goes beyond just looking at cells under a microscope. The World Health Organization now classifies brain tumors primarily based on their molecular features — meaning the specific genes and proteins found in the tumor cells.^[15]

One of the most important genetic tests looks for mutations in the IDH1 or IDH2 genes. Glioblastomas typically do not have mutations in these genes, which is why they are called “IDH-wildtype” (the term “wildtype” means the gene is unchanged).^[9][15] This distinguishes glioblastoma from other types of brain tumors that do have IDH mutations and generally have a better outlook.

Another important test is the MGMT methylation test. MGMT is a protein that can repair DNA damage caused by chemotherapy.^[9] If the MGMT gene is turned off (methylated) in the tumor cells, the tumor cannot repair the damage from chemotherapy, which means the treatment is more likely to work. If MGMT levels are high (non-methylated), chemotherapy may be less effective.^[9] This information helps doctors predict how well the tumor will respond to treatment.

Additional genetic alterations that doctors may look for include changes in the TERT gene, the EGFR gene, and abnormalities in chromosomes 7 and 10.^[15] Through advanced genomic profiling, researchers have identified that glioblastomas have a very complicated genetic makeup, with changes in multiple signaling pathways that control cell growth and survival.^[5] Each glioblastoma is different from the next, which is why a personalized approach to treatment based on genetic testing is necessary.^[8]

Diagnostics for Clinical Trial Qualification

When considering participation in a clinical trial, patients typically undergo the same core diagnostic tests described above — neurological examination, MRI or CT imaging, and tissue biopsy with molecular testing. However, clinical trials often have specific eligibility criteria that require additional testing or documentation to ensure patients meet the study requirements.

The standard diagnostic approach still forms the foundation. Imaging with MRI is used to measure the size and location of the tumor, and this baseline measurement will be compared to future scans to see if the treatment is working.^[10] The tissue biopsy confirms the diagnosis and provides information about the tumor’s genetic characteristics, which many clinical trials use to select appropriate patients.

For example, some clinical trials may only enroll patients whose tumors have specific molecular features, such as MGMT methylation status or particular gene mutations.^[9] Other trials may require that patients have newly diagnosed glioblastoma rather than recurrent disease, or vice versa. Some studies focus on patients whose tumors are large and cannot be completely removed by surgery.^[14]

Blood tests are commonly required to check overall health and organ function before enrolling in a clinical trial. These tests ensure that patients are healthy enough to tolerate the experimental treatment and monitor for any side effects during the study.^[11] Specific blood tests might include blood cell counts to make sure the bone marrow is functioning properly, and tests of kidney and liver function to ensure these organs can process the medications.

Advanced imaging techniques may also be part of clinical trial protocols. For instance, trials testing new radiation approaches may use 18F-DOPA PET scans combined with MRI to map the most active regions of the tumor with high precision.^[13] This helps researchers target treatment more accurately and measure the response to therapy.

Some trials may require documentation of the patient’s functional status through standardized scales that measure how well they can perform daily activities and whether they have any neurological deficits. This information helps researchers understand the tumor’s impact on quality of life and track changes during treatment.