S100B Unit Converter
S100B Unit Converter
µg/L and ng/mL are the same number for S100B — a melanoma marker that is also used in Scandinavia to avoid a CT scan after mild head injury, with a threshold of 0.10 µg/L within six hours of the injury.
S100B converter
Mass ladder onlyS100B 0.06 µg/L, sampled 3 hours after a mild head injury
Formula and conversion factors
pg/mL = µg/L × 1000
- µg/L = ng/mL
- a microgram per litre and a nanogram per millilitre are the same concentration, so nothing is calculated between them
- no molar unit
- S100B is reported as a mass concentration against an assay calibrator; no clinical threshold is written in molar units
- 0.10 µg/L
- the Scandinavian Neurotrauma Committee threshold for discharging an adult with mild head injury without CT, valid only when the sample is taken less than six hours after the trauma
- extracranial injury
- S100B is released from bone, fat and muscle as well as from brain, so fractures and soft-tissue trauma raise it and invalidate the head-injury rule-out in polytrauma
Worked example
S100B 0.06 µg/L, sampled 3 hours after a mild head injury
0.06 µg/L = 0.060 ng/mL — the two units are identical
0.06 × 1000 = 60 pg/mL
Below the 0.10 µg/L Scandinavian threshold, and the sample was taken inside the six-hour window
In a patient who meets the guideline's criteria and has no extracranial injury, this supports discharge without CT — a decision for the treating clinician
The three units
| Unit | Relationship | Example |
|---|---|---|
| µg/L | The usual reporting convention | 0.060 |
| ng/mL | Identical to µg/L | 0.060 |
| pg/mL | µg/L × 1000 | 60 |
The Scandinavian head-injury rule-out
| Element | What the guideline says |
|---|---|
| Threshold | S100B below 0.10 µg/L permits discharge without a CT head scan |
| Time window | The sample must be taken less than six hours after the trauma |
| Who it applies to | Adults with mild head injury: GCS 14 with no risk factors, or GCS 15 with loss of consciousness or repeated vomiting and no other risk factors |
| Who it excludes | Anticoagulant therapy or a coagulation disorder, post-traumatic seizure, signs of a depressed or basal skull fracture, and focal neurological deficit — these patients get a CT regardless |
| What invalidates it | Extracranial injury. S100B is released from bone, fat and muscle, so fractures and soft-tissue trauma raise it and the rule-out cannot be used in polytrauma |
| What it is not | It is not a melanoma threshold, and it is not a test for concussion or for how bad a head injury feels |
One protein, two entirely separate jobs
S100B is reported in µg/L or in the numerically identical ng/mL, with pg/mL a thousand times larger, so nothing needs calculating between the first two. There is no molar column: the protein is measured as a mass concentration against an assay calibrator and every published threshold is written that way. What makes S100B unusual is not its arithmetic but that the same result answers two unrelated questions depending on why it was requested.
The use that surprises people is in the emergency department. The Scandinavian Neurotrauma Committee guideline allows an adult with mild head injury to be discharged without a CT head scan if S100B is below 0.10 µg/L in a sample taken less than six hours after the trauma. It is a narrow rule. It applies to patients with a Glasgow Coma Scale of 14 without risk factors, or 15 with loss of consciousness or repeated vomiting, and it excludes anyone on anticoagulants, with a coagulation disorder, with a post-traumatic seizure, with signs of a skull fracture or with a focal neurological deficit. Those patients are scanned whatever the biomarker shows.
The rule also breaks in polytrauma, and this is the failure mode worth remembering. S100B is not specific to the brain: it is released from bone, fat and muscle as well, so fractures, bruising and soft-tissue injury raise the level without any intracranial damage. In a patient with injuries elsewhere the test loses its ability to exclude anything, and the six-hour window matters for the same reason — outside it, the number no longer answers the question that was asked.
The other life of S100B is in malignant melanoma, where it is used as a prognostic marker and in follow-up of advanced disease, usually alongside lactate dehydrogenase and imaging. The head-injury threshold has nothing to do with that setting and should not be read across to it, and melanoma cut-offs are themselves assay-specific, so a patient should be followed on a single platform. As with every marker on this site, an S100B result is one input to an assessment made by a clinician who has the history and the images; it is not a diagnosis and not a discharge decision on its own.
Frequently asked questions
Is µg/L the same as ng/mL for S100B?
Yes, exactly the same number — a microgram per litre is a nanogram per millilitre. Only pg/mL differs, being a thousand times larger, so 0.060 µg/L is 0.060 ng/mL and 60 pg/mL. There is no molar unit for S100B.
What is the S100B cut-off for avoiding a CT scan after a head injury?
The Scandinavian Neurotrauma Committee guideline uses 0.10 µg/L: below that, in an adult with mild head injury whose sample was taken less than six hours after the trauma and who meets the guideline’s criteria, the patient may be discharged without a CT head scan. It is a clinical decision made by the treating team, not by a number alone.
Why does the sample have to be taken within six hours?
Because S100B rises quickly after injury and is cleared quickly, with a short half-life. Outside that window a low result no longer reliably excludes an intracranial injury, so the guideline restricts the rule-out to samples drawn less than six hours after the trauma.
Why does a broken bone affect the head-injury result?
S100B is not specific to the brain. It is also released from bone, fat and muscle, so fractures, bruising and soft-tissue trauma raise the blood level with no intracranial injury present. In a patient with injuries elsewhere the rule-out cannot be used and imaging is decided on clinical grounds.
Is the same threshold used for melanoma?
No. The 0.10 µg/L figure is a head-injury decision rule and should not be read across to cancer follow-up. In melanoma, S100B is used as a prognostic marker and in monitoring advanced disease alongside LDH and imaging, with assay-specific cut-offs, so a patient should be followed on one platform.
Related calculators
References
- Undén J, Ingebrigtsen T, Romner B; Scandinavian Neurotrauma Committee. Scandinavian guidelines for initial management of minimal, mild and moderate head injuries in adults: an evidence and consensus-based update. BMC Med. 2013;11:50.
- Calcagnile O, Anell A, Undén J. The addition of S100B to guidelines for management of mild head injury is potentially cost saving. BMC Neurol. 2016;16:200.
- Weide B, Elsässer M, Büttner P, et al. Serum markers lactate dehydrogenase and S100B predict independently disease outcome in melanoma patients with distant metastasis. Br J Cancer. 2012;107(3):422–428.
Medical Disclaimer: The tools and content provided here are for educational and reference purposes only. They are not intended to substitute for professional medical advice, diagnosis, or treatment. Clinical decisions should always be based on the comprehensive assessment of a qualified healthcare professional.