If you've ever wondered, "What does a spinal tap test for?" you're probably curious about its purpose and why it's often used to diagnose complex medical issues. A spinal tap, also called a lumbar puncture, involves collecting cerebrospinal fluid (CSF) for analysis, providing physicians with information about a patient's central nervous system.
Cerebrospinal fluid surrounds the spinal cord and brain, performing various roles, such as acting as a shock absorber for the brain and spinal cord, transporting nutrients to both, regulating temperature in the central nervous system, and removing waste products.
What does a spinal tap test for? Key diagnostic roles
Spinal taps are typically used to check for abnormalities in the central nervous system like:
- Infections: Spinal taps are used to diagnose bacterial, fungal, or viral infections like meningitis or encephalitis.
- Autoimmune disorders: Spinal taps are used to help identify autoimmune disorders that can alter CSF composition, such as multiple sclerosis (MS) or Guillain-Barré syndrome (GBS).
- Bleeding in the spine or brain: A spinal tap can detect if blood has seeped into CSF by assessing protein, glucose, and cell count levels.
- Spinal leaks: Spinal taps continue to be used to diagnose spinal leaks despite research indicating that non-invasive diagnostic tools like the Bern Score are more accurate to diagnose the condition.
- Cancer: Lumbar punctures can also detect if cancer has reached the brain and monitor its progression.
Spinal taps involve using a thin, long, hypodermic needle to draw out cerebrospinal fluid. The fluid is then analyzed, focusing on its clarity, color, and composition.
What to expect during the spinal tap procedure
While a lumbar puncture comes with its share of risks, like up to 60% of patients it's administered on developing post-dural puncture headaches (PDPH), it's typically a straightforward procedure.
The test usually involves the patient lying on one side with their knees pulled to their chest to expose the part of their lower back where the needle will be inserted so a small CSF sample can be collected. The procedure lasts less than an hour, and most patients report mild discomfort afterward. Recovery is typically quick.
Using the procedure to diagnose spinal leaks often involves assessing opening pressure levels for signs of a leak. However, this approach is now outdated as research shows that non-invasive imaging methods are more accurate without the risk of creating new spinal leaks. Testing opening pressure to verify the presence of a spinal leak is inappropriate and risky since spinal CSF leaks cause low CSF volume rather than any specific pressure reading.
Interpreting the results of spinal taps
The cerebrospinal fluid sample collected during a lumbar puncture reveals a wealth of information about the patient's central nervous system. Physicians look for variations in protein content, glucose levels, and white blood cell count to diagnose patients.
- White blood cells: An elevated white blood cell count often signals some type of infection, while normal levels can help rule them out.
- Protein levels: Abnormally high levels of CSF in protein could indicate spinal cord or nerve damage.
- Glucose levels: Low glucose levels in cerebrospinal fluid could signify a bacterial infection.
- Opening pressure: CSF opening pressure is sometimes wrongly used to diagnose spinal leaks, with low readings pointing toward leaks.
Recovering after a spinal tap: What are the risks?
Getting a lumbar puncture comes with some risks, as is the case with other medical procedures. Some of the more common possibilities include:
- Post-dural puncture headaches (PDPH): As many as 60% of people who get spinal taps experience post-dural puncture headaches caused by slight changes in CSF pressure or a spinal leak.
- Spinal leaks: Spinal leaks are another common risk of lumbar punctures, often due to physicians using oversized needles. While there's a common misconception that PDPH is self-limiting, research doesn't support it. Many patients with dural punctures require multiple epidural blood patches to help close the leak. An epidural blood patch provides instant relief because of the tamponade effect, but research shows it's most effective when administered 48 hours after the puncture.
- Back pain: Lasting back pain at the site of a lumbar puncture is often a sign a leak has developed, especially when combined with PDPH.
- Infection: While extremely rare, a lumbar puncture can lead to an infection when proper sterilization protocols aren't followed.
While some sources state that patients can typically recover quickly from spinal taps, this fact is greatly determined by factors such as gender, needle size, and needle type. It is not uncommon for total disability to occur for months or even years in female patients, particularly when needles associated with high PDPH rates are used.
A spinal tap isn't always your best option
Spinal taps test for various health issues by collecting and analyzing small cerebrospinal fluid samples. Changes in the composition of CSF typically signal an underlying problem.
One of the most controversial truths about lumbar punctures is the incredibly high rate of dural punctures, primarily when certain needle types and sizes are used, such as larger, traumatic needles instead of smaller, atraumatic ones.
Despite medical literature showing that the likelihood of PDPH can be reduced through using a lower-risk needle, many physicians still don’t make it standard practice to do so. Anecdotally, petite women and teenage girls experience more severe symptoms and disability after a spinal tap, and they often report that physicians did not adapt and use a smaller needle despite their smaller body sizes.
Arguably, a needle of any size will cause a dural injury. Patients have reported symptoms even after a 26-gauge needle was used for a lumbar puncture. However, patient feedback indicates that smaller punctures with an atraumatic needle are easier to recover from because of the body’s partial healing and compensatory responses to spinal CSF leaks.
Even if total dural closure wasn’t achieved, these patients can often function without treatment with minimal discomfort and secondary symptoms. However, there is always the chance that the location of the spinal leak can reopen in the future if strained.
The best comparison is a small tear in a piece of clothing. As the saying goes, “A stitch in time saves nine.” Similarly, gathering information from patient feedback shows the dura membrane appears susceptible to further tearing over the years, leading to increased symptoms, even if patients start with a small puncture if this puncture is not promptly and correctly patched.
The ongoing spinal leak care crisis
The use of a lumbar puncture for diagnosing dural punctures has increased the number of patients with a spinal leak. Physicians working with outdated information are quick to recommend spinal taps despite non-invasive methods like the Bern Score in reading brain MRIs being more accurate at diagnosing intracranial hypovolemia as the result of a spinal leak when combined with a review of a patient’s medical history. The high costs of the risks associated with lumbar punctures make such low-risk diagnostic tools like the Bern Score more attractive.
Always ask your physician if a lumbar puncture is your only option if it's recommended. In many cases, non-invasive alternatives might be available.
The reality of spinal taps is that many patients are left disabled after the procedure due to undiagnosed dural punctures that lead to persistent spinal leaks. The current spinal leak crisis has created a $1 trillion underserved market, making it an excellent time for healthcare professionals, like anesthesiologists, to transition to private practices.
