Unit Converter
S100
(Calcium-Binding Protein Family - Key Marker in Melanoma, Brain Injury, Neuroinflammation & Critical Care Monitoring)
Synonyms
- S100
- S100 protein
- S100B (most clinically used isoform)
- S100A1, S100A2 (family members)
- Melanoma-associated antigen (S100B)
- Neurotrophic S100 protein
Note: In clinical practice, S100B is the predominant measurable isoform.
Units of Measurement
- ng/mL
- ng/dL
- ng/100 mL
- ng%
- ng/L
- µg/L
Unit Conversions
1 ng/mL=1000 ng/L1\ \text{ng/mL} = 1000\ \text{ng/L}1 ng/mL=1000 ng/L 1 ng/mL=1 µg/L1\ \text{ng/mL} = 1\ \text{µg/L}1 ng/mL=1 µg/L 1 ng/mL=100 ng/dL1\ \text{ng/mL} = 100\ \text{ng/dL}1 ng/mL=100 ng/dL \text{ng%} = \text{ng/dL}
Description
S100 proteins are a family of calcium-binding proteins found in:
- Glial cells (astrocytes, Schwann cells)
- Melanocytes
- Chondrocytes
- Adipocytes
The clinically important analyte is S100B, released during:
- Melanoma tumor activity
- Astrocyte injury
- Traumatic brain injury (TBI)
- Stroke
- Hypoxic brain damage
- Neuroinflammation
S100B enters bloodstream when the blood–brain barrier is disrupted or when neoplastic cells release it.
Physiological Role
- Intracellular calcium signaling
- Neuronal repair signaling
- Regulation of cell growth and apoptosis
- Glial activation
- Melanocyte differentiation
Clinical Significance
HIGH S100 (S100B)
1. Malignant Melanoma (Primary Use in Oncology)
- S100B correlates with tumor burden
- Elevated in:
- Metastatic disease
- Progression/recurrence
- Advanced-stage melanoma
- Metastatic disease
High S100B = Poor prognosis
Used with LDH and imaging to monitor disease.
2. Traumatic Brain Injury (TBI)
- Rapid rise within minutes after head trauma
- Helps rule out intracranial injury
- Used in emergency settings to guide CT need (Europe, NICE/ Scandinavian guidelines)
Interpretation in TBI
| S100B | Interpretation |
| <0.10 µg/L (100 ng/L) | Low risk of intracranial injury |
| >0.10–0.20 µg/L | Possible mild TBI |
| >0.20 µg/L | High risk – consider CT/intervention |
3. Stroke
- Elevated in:
- Ischemic stroke
- Hemorrhagic stroke
- Predicts infarct size & outcomes
- Ischemic stroke
4. Neuroinflammation
Occurs in:
- Multiple sclerosis
- Encephalitis
- Meningitis
5. Cardiac Arrest / Hypoxic Brain Injury
Post-resuscitation elevation predicts:
- Severity of brain injury
- Neurological outcome
6. Neurosurgical Procedures
Transient elevation after:
- Craniotomy
- Neurosurgery
- Prolonged seizures
LOW / NORMAL S100
A normal value does not rule out:
- Melanoma (early stage)
- Concussion
- Small intracranial lesions
Reference Intervals
(Tietz 8E + Mayo + ARUP + Neurotrauma Guidelines)
Serum S100B
- <0.105 µg/L (= <0.105 ng/mL) in adults
- Children have slightly higher normal upper limits
CSF S100B
- <0.5 µg/L
Melanoma Cutoffs
| Stage | Typical Levels |
| Localized | Normal or slight ↑ |
| Regional disease | ↑ (0.2–0.5 µg/L) |
| Metastatic | Often >0.5–1.0 µg/L |
Brain Injury Cutoffs
- >0.10 µg/L (100 ng/L) → possible TBI
- >0.20 µg/L → increased risk of intracranial lesion
Diagnostic Uses
1. Melanoma Monitoring
- Follow-up
- Detection of recurrence
- Prognosis
- High values → consider imaging
2. Traumatic Brain Injury
- Screening
- CT triage tool
- Monitoring brain injury progression
3. Stroke
- Prognostic indicator
4. Hypoxic-Ischemic Injury
- Post–cardiac arrest outcome prediction
5. Neuroinflammatory Disorders
- MS relapses
- Encephalitis
- Meningitis
Analytical Notes
- Sample: serum
- S100B is stable; no fasting required
- Hemolysis may interfere (RBCs contain S100A)
- Immunoassays (ELISA, electrochemiluminescence)
- Must interpret with clinical context + imaging
Clinical Pearls
- S100B >1.0 µg/L in melanoma strongly correlates with metastatic disease.
- In TBI, S100B has a very high negative predictive value - low value can exclude serious injury.
- S100B rises rapidly (within 30 minutes) after trauma and falls within hours.
- S100B may falsely elevate in:
- Renal failure
- Strenuous exercise
- Burns
- Hemolysis
- Renal failure
Interesting Fact
S100B was named because it is soluble in 100% saturated ammonium sulfate - a unique biochemical property discovered in the 1960s.
References
- Tietz Clinical Chemistry & Molecular Diagnostics, 8th Edition - Tumor Markers & Neurobiomarkers
- NCCN Melanoma Guidelines
- EANO Neuro-Oncology Biomarker Guidelines
- Mayo Clinic Laboratories - S100B
- ARUP Consult - S100 Protein
- Scandinavian Neurotrauma Committee (SNC) S100B Guidelines
- NIH / MedlinePlus - S100 Test