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Patient guide · 4 min read

Thermal threshold testing (QST), quantifies small fibre function in painful peripheral neuropathy.

Thermal threshold testing (quantitative sensory testing, QST) quantifies warm, cold, heat pain and cold pain thresholds - the functional counterpart to skin biopsy for small fibre neuropathy diagnosis and monitoring.

How it’s done

From consultation to structured QST report - step by step.

A standardised protocol using either the method of levels or the method of limits, with thresholds compared to age- and site-matched normative data.

  1. 01

    Neurology / pain consultation

    Clinical history, symptom mapping and pre-test probability set the plan.

  2. 02

    QST device applied to hand and foot

    A thermode is placed at a standardised site on the hand dorsum and foot dorsum.

  3. 03

    Warm threshold

    Temperature rises from baseline until the first sensation of warmth is reported.

  4. 04

    Cold threshold

    Temperature falls from baseline until the first sensation of cool is reported.

  5. 05

    Heat pain threshold

    Temperature rises further until warmth becomes just painful - recorded and stopped.

  6. 06

    Cold pain threshold

    Temperature falls further until cool becomes just painful - recorded and stopped.

  7. 07

    Structured report

    Thresholds are compared to age- and site-matched normative data, with a clinical impression.

What it shows

The patterns QST reveals.

Threshold changes map to specific fibre populations - and to specific clinical syndromes.

  • Elevated warm threshold

    C-fibre dysfunction - the earliest QST signature of small fibre neuropathy.

  • Elevated cold threshold

    A-delta fibre dysfunction, often paired with the warm-threshold abnormality.

  • Elevated heat pain threshold

    Loss of nociceptive C-fibre function; typical of length-dependent SFN.

  • Elevated cold pain threshold

    Loss of A-delta nociceptive function; supports a small fibre lesion.

  • Length-dependent SFN pattern

    Foot thresholds abnormal, hand thresholds preserved - the classic pattern.

  • Non-length-dependent SFN

    Hand and foot both abnormal - think Sjögren’s, sarcoid, paraneoplastic causes.

  • Central sensitisation pattern

    Lowered pain thresholds with preserved detection - a nociplastic pain signature.

  • Red flag: bilateral loss with autonomic collapse - urgent neurology

    Amyloid, vasculitic and paraneoplastic SFN can present this way - do not wait.

Red flags

When SFN needs urgent neurology.

These presentations warrant same-week neurology review and an accelerated aetiological work-up.

  • Bilateral thermal loss with autonomic collapse

  • Rapidly progressive SFN

  • Post-COVID SFN

  • Sjögren’s vasculitis

  • Amyloid neuropathy

  • Paraneoplastic SFN

  • Post-chemotherapy SFN

  • Post-immunotherapy SFN

  • Post-vaccination SFN

Treatment options

The pathways after a small fibre neuropathy diagnosis.

Treatment is aetiology-directed where possible, with symptomatic control alongside - and MDT input where the picture is complex.

  • Treat underlying cause

    Diabetes, Sjögren’s, sarcoid, coeliac, B12, thyroid, HIV, HCV - the yield of an aetiology work-up is high.

  • Gabapentin / pregabalin

    First-line neuropathic-pain agents per NICE CG173; titrated to response and tolerability.

  • Duloxetine

    SNRI first-line for painful diabetic neuropathy; useful across many SFN aetiologies.

  • Topical lidocaine / capsaicin

    For focal or patchy pain, particularly where oral agents are poorly tolerated.

  • Autonomic support

    Compression, hydration, salt, midodrine or fludrocortisone where autonomic SFN is present.

  • Physio for reconditioning

    Graded activity, balance work and desensitisation - quality-of-life gains beyond drugs alone.

  • Neurology follow-up

    Serial QST to track progression or treatment response, with re-work-up if the picture shifts.

  • MDT review

    Neurology, rheumatology, pain medicine and immunology together where the aetiology is complex.

Frequently asked

Everything patients ask about QST.

What the test measures, whether it hurts, how long it takes, and when a skin biopsy follows.

  • What is thermal threshold testing?

    Thermal threshold testing - a form of quantitative sensory testing (QST) - measures the smallest change in skin temperature you can detect (warm and cold) and the point at which warmth or cool becomes painful. It quantifies small fibre function, which routine nerve conduction studies cannot assess.

  • Why is QST used in small fibre neuropathy?

    Small fibres (A-delta and C) carry thermal and pain sensation and are invisible to nerve conduction studies. QST is the functional test of choice for small fibre neuropathy and pairs with intraepidermal nerve fibre density (IENFD) on skin biopsy as the structural test.

  • Does the test hurt?

    The thermal detection thresholds are not painful. The pain thresholds are, by definition, taken to the just-painful point and then stopped - brief and controlled, and you are in charge of the response button throughout.

  • How long does it take?

    30–45 minutes for a standard hand-and-foot protocol, including set-up, familiarisation and the four thresholds at each site.

  • Do I need to prepare?

    Avoid caffeine, alcohol and analgesia if possible on the day, and bring a list of your current medications. No fasting is required.

  • When would I need a follow-up skin biopsy?

    Where QST is abnormal, a 3 mm punch biopsy of the distal leg for IENFD gives the structural confirmation and quantifies severity. The two together are the accepted diagnostic pairing.

Sources

Guidelines this page draws on.

Last updated 2026-07-30 · Next review 2027-07-30.

Related tests

Related diagnostic pathways.

In practice, in London

What thermal threshold testing looks like on the ground in London

With thermal threshold testing, the London question is usually about report turnaround and the radiologist reading it - not whether the scan is available. Public provision for thermal threshold testing is competent but constrained by capacity. Private London clinics tend to have shorter diaries and longer appointment slots, so you get the same specialists with more time. For people who’ve been going round in circles with primary care, that first proper conversation is often what shifts things.

A typical private booking for thermal threshold testing in London starts with a consultant conversation - sometimes in person on Harley Street or Marylebone, sometimes on video if that suits better. Any imaging or diagnostics happen at a nearby CQC-registered facility, and reports usually land within 24 to 72 hours. The whole loop, from first call to written report, is often done inside a fortnight. For thermal threshold testing specifically, the difference between a routine report and a sub-speciality read is where private care earns its keep.

The value is knowing which consultant reads this particular presentation best, which unit turns reports around fastest, and which pathway won’t hit a dead end if the findings point somewhere unexpected.