The purpose of this study is to determine the negative predictive value of protein S100B that could exclude subarachnoid and intracranial haemorrhage for patient that present severe headache within the last 3 hours.

This study will be proposed to every patient that correspond to eligibility criteria, such as presenting a severe headache (Visual Analog Scale ≥ 6/10) within 3 hours before arriving to the emergency.

After signing the informed consent, a blood sample will be taken in order to dosage S100B protein of each patient, and then they will have a brain scan.

The trial ends after the brain scan for each patient. Results of brain scans will be compared with results of S100B dosage.

Inclusion Criteria:

• Male or female over 18 years-old
• Patient presenting at the Emergency Service a non-traumatic severe headache lasting for less than 3 hours. The severity is defined as a VAS ≥ 6/10
• Blood sample can be taken within 1 hour following the emergency admission
• VAS > 6 or Glasgow < 8
• Signed and dated informed consent by patient, or trusted person, or family

Exclusion Criteria:

• Patient presenting headache after head trauma
• Pregnant or breastfeeding women
• Patient with a pathology causing the elevation of PS100B's rate such as Alzheimer's disease, Creuzfeld-Jacob's disease, Multiple Sclerosis, cerebral tumour, trisomy 21, melanoma (diabetes excluded)
• Patient covered by social security regimen or equivalent
• Patient under guardianship (legal protection)
• Patient deprived of liberty by court or administrative order
• Any condition that could influence PS100B's dosage results according to the physician.

The population will be recruited in the emergency unit

There is no IPD sharing plan