LLNA EC3 Dermal Sensitization

Interpolate LLNA EC3 at stimulation index three from monotone bracketing tested concentrations; does not perform an assay, classify sensitization or extrapolate untested concentrations.

Description

Interpolate the tested concentration at stimulation index three in a monotone LLNA response series.

The local lymph node assay, or LLNA, measures lymph-node proliferation in a skin-sensitization assessment. A stimulation index compares treated response with the relevant control; EC3 denotes the test concentration associated with an index of three.^[1]

This tool receives stimulation indices already calculated for positive tested concentrations. It returns an EC3 by straight-line interpolation in concentration space, requiring the target to be observed exactly or bracketed by the supplied responses.

Concentrations are entered as percentages: 1 means 1%, not a fraction of 0.01. The output is also a percentage. An EC3 summary is not a full assay validity review or a clinical allergy-risk prediction.

When to use LLNA EC3 Dermal Sensitization

Use it to reproduce bracketed EC3 arithmetic from a prepared, nondecreasing LLNA response series. Supply treated concentrations; a zero-concentration control is not an accepted interpolation entry.

How to use LLNA EC3 Dermal Sensitization and interpret its calculation

Enter at least two testConcentrationsPercent in strictly increasing order, each greater than zero and no greater than 100.
Enter aligned nonnegative stimulationIndices in nondecreasing order.
Run the calculation and read ec3ConcentrationPercent. If the target is not bracketed, review the experiment or use an appropriately justified method rather than extrapolating with this tool.

EC3 = Cbelow + (3 − SIbelow) × (Cabove − Cbelow)/(SIabove − SIbelow)

Interpolation uses the first entry with SI at least three and the preceding entry, unless an exact target is present.

If a supplied index equals three, the implementation returns the first corresponding concentration. If the first index exceeds three or no index reaches three, it rejects the series. Decreasing indices are rejected even if a local pair could bracket three.

json

{
  "input": {
    "testConcentrationsPercent": [
      1,
      2,
      4
    ],
    "stimulationIndices": [
      1,
      2,
      4
    ]
  },
  "output": {
    "ec3ConcentrationPercent": 3
  }
}

Response plateaus are allowed. If the first index is exactly three, the first concentration is returned. If every index is below three, no finite bracketed EC3 is returned. A zero control concentration must be kept outside the treated interpolation list.

Limitations and assumptions

It does not calculate stimulation indices, select a control, assess assay validity, model cytotoxicity, or test statistical uncertainty. It supplies no extrapolation or concentration-response fitting.

Linear interpolation depends on concentration spacing and the supplied mean responses. An EC3 estimate does not independently establish human potency, sensitizer classification, or safe exposure.

Alternative or Complementary methods

Use model-based dose-response methods when a fitted benchmark is appropriate, with an endpoint and model chosen for the data. A NOEC summary uses significance tests and answers a different endpoint-selection question.

References

Test No. 429: Skin Sensitisation (2010) — Organisation for Economic Co-operation and Development

Similar or alternative tools

Benchmark Dose Probit
Calculate a benchmark from an externally fitted quantal probit response model, when that model is appropriate.
NOEC
Select a concentration endpoint from supplied control-comparison p-values.