From the Guidelines
An INR of 1.5 or less is recommended for lumbar puncture.
Rationale for INR Threshold
- The UK Joint Specialist Societies guideline on the diagnosis and management of acute meningitis and meningococcal sepsis in immunocompetent adults recommends that an LP should not be routinely performed at an INR of 1.5 or higher 1.
- This guideline suggests that the risks of reversing warfarin should be weighed against the benefits of performing an LP, implying that an INR above 1.5 may increase the risk of bleeding complications.
- While the exact incidence of post-LP hematomas is unknown, the risk is increased in patients with abnormal clotting, and an INR threshold of 1.5 or less is a reasonable precaution to minimize this risk.
Considerations for Other Anticoagulants
- For patients on low molecular weight heparin (LMWH), the LP should not be performed until 12 hours after the last dose, and prophylactic LMWH can be started 4 hours after the procedure 1.
- For patients on unfractionated heparin, the risk of spinal hematomas is negligible if the heparin is given after at least 60 minutes, and heparin can be restarted 1 hour after an LP 1.
- Patients receiving newer oral anticoagulants, such as apixaban, dabigatran etexilate, and rivaroxaban, should be discussed with a haematologist, as trials are ongoing regarding specific reversal agents for these drugs 1.
From the Research
International Normalized Ratio (INR) for Lumbar Puncture
- The INR threshold for lumbar puncture is generally considered to be 1.4 or less, as stated in the study 2.
- A study published in 2015 reported the use of low-dose prothrombin complex concentrate to reverse an INR of >3 to 1.3, allowing for a safe lumbar puncture to be performed 3.
- Another study from 2016 found that prothrombin complex concentrates can be effective in reversing vitamin K antagonist to enable emergency lumbar puncture, with a target INR of less than or equal to 1.5 4.
- The Association of British Neurologists clinical guideline from 2018 provides recommendations for periprocedural antithrombotic management for lumbar puncture, but does not specify a specific INR threshold 5.
- It is worth noting that the INR threshold may vary depending on the specific clinical context and patient population, and that other factors such as platelet count and bleeding risk should also be considered when deciding whether to perform a lumbar puncture.
Specific INR Values
- An INR of 1.5 to 2.0 was associated with a higher frequency of traumatic lumbar punctures (36.8%) compared to those with a normal INR (28.2%) 2.
- An INR of 2.1 to 2.5 was associated with a higher frequency of traumatic lumbar punctures (43.7%) compared to those with a normal INR (28.2%) 2.
- An INR of 2.6 to 3.0 was associated with a higher frequency of traumatic lumbar punctures (41.9%) compared to those with a normal INR (28.2%) 2.