At a Glance
- S100B is a protein released into the blood when melanocytes or brain cells are damaged or unusually active
- Used primarily as a tumour marker in malignant melanoma — for monitoring, not initial diagnosis
- Also used to assess neurological injury after brain trauma or stroke
- Normal range: 0–0.1 µg/L
- A single elevated result is not diagnostic on its own — always interpreted alongside imaging and clinical context
What is S100?
S100 refers to a family of calcium-binding proteins found in various cells throughout the body. In clinical testing, "S100" almost always refers to S100B — the subtype used as a serum biomarker.
S100B plays a role in cell growth, differentiation, and cellular stress responses. Under normal conditions, only very small amounts circulate in the blood. Levels rise when cells are damaged or proliferating abnormally — most significantly in malignant melanoma and in neurological injury.
This marker may appear on your lab report as S100, S100B, or S100 (Malignant Melanoma).
Normal range What a typical result looks like and what it means.
The normal upper limit for S100B is typically 0.1 µg/L (equivalent to 100 ng/L). Reference ranges vary slightly between laboratories, so always compare your result to the range printed on your own report.
A result within the normal range means S100B levels are not significantly elevated — this is reassuring in the context of melanoma monitoring.
Why is S100 tested?
S100B is primarily ordered in the context of malignant melanoma, where it serves as a tumour marker. It is not used for initial diagnosis — melanoma is diagnosed by biopsy — but is valuable for:
- Monitoring disease progression — rising levels over time may indicate advancing disease
- Assessing treatment response — falling levels after treatment suggest the therapy is working
- Detecting recurrence or metastasis — an increase after a period of stability warrants further investigation
S100B may also be measured in neurology to evaluate blood-brain barrier disruption, such as after traumatic brain injury or stroke, as brain cells release S100B when damaged.
What does an elevated S100 result mean?
An elevated S100B result (above 0.1 µg/L) means more S100B protein than normal is circulating in your blood. In the context of melanoma monitoring, this may indicate:
- Disease progression or spread
- Incomplete response to treatment
- Recurrence after a period of remission
However, S100B is not specific to melanoma. Mildly elevated results can also occur in other conditions including brain injury, stroke, some inflammatory conditions, and after strenuous physical exercise. A single elevated result is not diagnostic on its own and should always be interpreted alongside imaging, clinical examination, and other markers such as LDH.
If your S100B is elevated, your oncologist or specialist will assess the result in the context of your full clinical picture before drawing conclusions or changing your management plan.
What does a normal S100 result mean?
A result within the normal range (0–0.1 µg/L) is reassuring. In melanoma monitoring, a consistently normal S100B suggests the disease is stable and not actively progressing. It does not guarantee the complete absence of disease, but is a positive signal when interpreted alongside imaging and clinical findings.
S100
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