A lumbar puncture (LP), often called a spinal tap, is a standard medical procedure used primarily for diagnosis. It involves inserting a thin needle into the lower back to collect cerebrospinal fluid (CSF) to test for conditions like meningitis, multiple sclerosis, or bleeding in the brain. Although generally safe, the LP is an invasive process that carries serious risks if the patient has certain underlying conditions. A careful screening process is mandatory to identify conditions where the procedure must be delayed or avoided entirely.
Situations Involving High Bleeding Risk
The most serious risk associated with an LP is uncontrolled bleeding, which can cause a spinal hematoma. A spinal hematoma is a collection of blood that can compress the spinal cord or nerves, potentially causing permanent paralysis or other severe neurological damage. This risk is linked to systemic conditions that impair the body’s ability to form blood clots.
Severe thrombocytopenia (low platelet count) is a major concern; a count below 50,000 per microliter is widely considered a contraindication. Coagulopathy, a disorder affecting clotting ability, such as an International Normalized Ratio (INR) above 1.5, also requires correction before the procedure. Patients taking anticoagulant medications (blood thinners) must have these drugs managed carefully before the LP.
Protocols require holding these medications for a specific period to allow clotting function to normalize, with timing depending on the drug type and dosage. For example, therapeutic doses of Low Molecular Weight Heparin (LMWH) require a 24-hour hold, and Warfarin may need five days to ensure the INR is safe. Direct Oral Anticoagulants (DOACs) also require specific holding periods. In emergencies, reversal agents may be administered to rapidly restore clotting function, but Aspirin monotherapy generally does not require holding.
Assessment for Increased Intracranial Pressure
The most life-threatening contraindication is significantly increased intracranial pressure (ICP) caused by a space-occupying lesion, such as a large tumor, abscess, or hematoma. Removing CSF from the lower spinal canal decreases pressure below the brain, creating an imbalance between the skull and spine. This shift can precipitate cerebral herniation, where brain tissue is forced downward through openings in the skull, leading to brainstem compression, coma, and potentially death.
Clinical signs of elevated ICP or impending herniation are paramount during assessment. These signs include a deteriorating level of consciousness, focal neurological deficits (weakness on one side of the body), or papilledema (swelling of the optic nerve head detected during an eye exam). If any of these high-risk signs are present, the lumbar puncture must be delayed.
Neuroimaging, typically a computed tomography (CT) scan of the head, is required before the LP to rule out a mass lesion causing the pressure. If the CT scan shows evidence of a significant mass or brain shift, the LP is absolutely contraindicated. If a life-threatening infection like bacterial meningitis is suspected, empiric antibiotics must be administered immediately, even before imaging or the LP, to prevent a dangerous delay in treatment.
Localized Infection and Spinal Anatomy Concerns
The presence of an active infection at the intended puncture site is a serious absolute contraindication for a lumbar puncture. A local skin infection, such as cellulitis or an abscess in the lower back, provides a direct pathway for bacteria to be introduced into the central nervous system (CNS) and the sterile CSF. Performing the procedure through infected tissue risks causing a severe complication like meningitis or an epidural abscess.
The procedural risk is averted by choosing an alternative, non-infected site for needle insertion, or by delaying the procedure until the localized infection is treated and cleared. Structural abnormalities of the spine are often considered relative contraindications.
Severe spinal deformities like scoliosis, or a previous spinal fusion surgery, can make it technically difficult to safely access the subarachnoid space. In these situations, the LP may still be possible but often requires specialized guidance. This guidance, such as using fluoroscopy or ultrasound, helps visualize the correct placement of the needle and avoid nerve damage.