Does having a lumbar puncture break the fast?

The fast is not broken by the insertion of an instrument into the brain, vertebra or spinal column for the purpose of examination or taking a sample from it.

The Islamic Fiqh Council has issued a statement on things that break the fast, as follows:

The following things do not have any effect on the fast:

1. Eye drops, ear drops, ear syringing, nose drops and nasal sprays – so long as one avoids swallowing any material that may reach the throat.
2. Tablets or lozenges that are placed beneath the tongue for the treatment of angina pectoris etc., so long as one avoids swallowing any material that reaches the throat.
3. Vaginal pessaries, douching, use of a speculum, or internal digital examination.
4. Introduction of a scope or coil (IUD), etc., into the uterus.
5. Introduction of a scope or catheter into the urethra (male of female), or injection of dyes for diagnostic imaging, or of medication, or cleaning of the bladder.
6. Drilling of teeth (prior to filling), extraction or polishing of teeth, using a miswaak or toothbrush, so long as one avoids swallowing any material that reaches the throat.
7. Rinsing, gargling or applying topical treatment in the mouth, so long as one avoids swallowing any material that reaches the throat.
8. Injections, whether subcutaneous, intra-muscular or intra-venous – with the exception of those used for purposes of nutrition.
9. Oxygen.
10. Anaesthetics, so long as they do not supply nutrition to the patient.
11. Medicines absorbed through the skin, such as creams, lotions and patches used to administer medication through the skin.
12. Introduction of a catheter into the veins in order to examine or treat the vessels of the heart or other organs.
13. Laparoscopy for the purpose of diagnosis or surgical treatment of the abdominal organs.
14. Biopsies of the liver and other organs, so long as this is not accompanied by the administration of nutrients.
15. Gastroscopy, so long as this is not accompanied by the administration of nutrients.
16. Introduction of medicine or instruments into the brain or spinal cord.
17. Involuntary vomiting (as opposed to self-induced vomiting).

And Allah knows best.