Enter filament sequence and withdrawal responses. Get Dixon 50% threshold with confidence intervals, filament response charts, and copy-paste methods text.
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Animals must be acclimated to the testing apparatus for at least 30 minutes (mice) or 15 minutes (rats) before testing begins. Grooming, exploratory behavior, and freezing will confound withdrawal responses if the animal is not habituated. Test in a quiet room with consistent lighting and minimal vibrations.
The filament must be applied perpendicular to the glabrous skin of the mid-plantar hind paw, avoiding the toe pads and heel. Push until the filament just bends (approximately 2–3 seconds of application). Angled application or excessive bending changes the applied force and introduces variability.
Inter-stimulus intervals of at least 30 seconds (mice) or 1–2 minutes (rats) are critical. Shorter intervals can cause temporal summation (wind-up), artificially lowering thresholds. If the animal is actively grooming or moving, wait for it to settle before applying the next filament.
Count only brisk paw withdrawal, paw shaking, or paw licking as positive responses. Do not count ambiguous weight shifting or slow postural adjustments. If unsure, repeat the stimulus after a 2-minute rest. Blinding to group assignment is essential for unbiased scoring.
Begin testing at a mid-range filament (typically 0.4–0.6 g for mice, 2.0 g for rats). Starting too low wastes trials approaching threshold from below; starting too high can cause sensitization. For longitudinal studies, use the same starting filament across all time points.
Implements the Chaplan et al. (1994) simplified Dixon up-down method for mechanical threshold estimation. After the first response direction change, the tool records 4 additional stimuli and maps the 6-character response pattern (XOOOXX etc.) to a k-value from the Dixon (1980) statistical tables. The 50% threshold is computed as 10^(Xf + kδ) / 10000. Standard filament sets for mice (0.02–4.0 g) and rats (0.4–15.0 g) are built in. All computation is client-side — no data leaves the browser.
Last validated 2026-04-05. Calculations are designed for planning and documentation support; verify procurement decisions against manufacturer specifications or institutional SOPs.
ConductScience Von Frey Up-Down Threshold Calculator (v1.0). ConductScience, Inc. 2026. Available at: https://conductscience.com/tools/von-frey-up-down-threshold-calculator
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 (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.
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 SEM).
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