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Von Frey Up-Down Threshold Calculator

Enter filament sequence and withdrawal responses. Get Dixon 50% threshold with confidence intervals, filament response charts, and copy-paste methods text.

Dixon Method50% ThresholdCSV Export

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Load example Von Frey data to see the full workflow

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  • Calculate 50% withdrawal thresholds from von Frey up-down testing sequences
  • Compare mechanical sensitivity between treatment groups (e.g., drug vs. vehicle)
  • Track threshold changes over time in longitudinal pain studies
  • Process batch data from multiple animals and generate publication-ready summaries
  • Generate methods text and export results for statistical analysis in R, Prism, or SPSS

Don't use for

  • Electronic von Frey data (continuous force measurement does not use Dixon method)
  • Frequency-based von Frey testing (requires different statistical approach)
  • Randall-Selitto or tail-flick tests (different pain modalities and analysis methods)

What Is Von Frey Testing?

Von Frey testing is the gold-standard method for measuring mechanical pain sensitivity (nociception) in rodents. Calibrated nylon monofilaments of graded stiffness are applied to the plantar surface of the hind paw, and the experimenter records whether the animal withdraws its paw in response. By systematically increasing or decreasing the filament force, the researcher identifies the mechanical threshold — the minimum force that reliably produces a withdrawal response. This threshold is a primary outcome measure in studies of neuropathic pain, inflammatory pain, analgesic drug efficacy, and nerve injury models.

The Up-Down Method Explained

The up-down method (Dixon, 1980; Chaplan et al., 1994) is a sequential testing strategy designed to efficiently estimate the 50% response threshold using far fewer trials than traditional methods. Testing begins at a mid-range filament. If the animal withdraws, the next-lighter filament is presented; if not, the next-heavier filament is applied. This continues until the first direction change (crossover) occurs — for example, a sequence of no-response, no-response, WITHDRAWAL marks the first crossover at the withdrawal. After this crossover, exactly 4 more stimuli are presented (for a total of 5–6 data points around the threshold). The pattern of positive (X) and negative (O) responses in this critical window is converted to a tabular k-value, which corrects for the discrete and sequential nature of the test. The 50% threshold is then calculated as 10^(Xf + kδ) / 10000, where Xf is the log value of the last filament, k is the pattern-dependent correction factor, and δ is the average log-unit spacing between filaments.

Interpreting Thresholds

The 50% withdrawal threshold represents the estimated force at which the animal would respond to 50% of presentations. Lower thresholds indicate heightened pain sensitivity (hyperalgesia or allodynia), while higher thresholds indicate reduced sensitivity. In practice, baseline thresholds for naive C57BL/6 mice are typically 0.6–1.4 g, while CFA-induced inflammatory pain can reduce thresholds to 0.07–0.16 g. For rats, naive baselines are typically 8–15 g, with SNL neuropathy models reducing thresholds to 1–4 g. When reporting results, express thresholds in grams (not log units) and use nonparametric statistical tests because the data are ordinal, not continuous. Always report both individual animal thresholds and group summaries (median or mean ±\pm SEM).

Frequently Asked Questions

Next Steps

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