What is the monofilament test?

Monofilament Test: A Standardized Approach for Detecting Diabetic Peripheral Neuropathy

The monofilament test is a standardized clinical examination using a 10g (5.07 Semmes-Weinstein) monofilament to assess protective sensation in the feet, primarily used to identify patients at risk for diabetic foot ulceration by detecting loss of protective sensation. 1

Test Preparation and Setup

• Conduct the examination in a quiet, relaxed setting to ensure patient focus and accurate responses 1
• Begin by demonstrating the test on the patient's hands, elbow, or forehead so they understand what sensation to expect 1
• Position the patient so they cannot see when or where you apply the monofilament 1

Testing Procedure

Proper Technique

• Apply the monofilament perpendicular to the skin surface 1
• Use sufficient force to cause the filament to bend or buckle 1
• Maintain skin contact for approximately 2 seconds total (approach, contact, and removal) 1
• Avoid sliding the monofilament across skin or making repetitive contact at the same site 1
• Apply the filament along the perimeter of, not directly on, any ulcer site, callus, scar, or necrotic tissue 1

Testing Protocol

• Test three standardized sites on each foot (typically plantar surface of hallux, first metatarsal head, and fifth metatarsal head) 1
• At each site:
  • Apply the monofilament twice at the same location 1
  • Include at least one "mock" application where no filament is applied 1
  • Ask the patient to respond "yes/no" when they feel pressure and identify which foot was touched 1
• Protective sensation is considered present if the patient correctly answers two out of three applications per site 1
• Protective sensation is absent with two out of three incorrect answers, indicating the patient is at risk for ulceration 1

Interpretation and Clinical Significance

• Loss of protective sensation (LOPS) indicates the presence of distal sensorimotor polyneuropathy and is a significant risk factor for diabetic foot ulceration 1
• The monofilament test assesses large-fiber function and protective sensation 1
• A simplified monofilament examination using only 4 sites per foot can detect 90% of patients with abnormal sensation compared to more extensive testing 2
• The inability to feel a 5.07 monofilament represents approximately 98% loss of normal sensory ability 3

Important Clinical Considerations

• Provide positive feedback to encourage patients during testing 1
• Be aware that monofilaments can lose buckling force if used for extended periods, affecting test reliability 1
• The monofilament test has better reproducibility compared to other neurological examination components such as pinprick, position sense, and vibration testing 2
• Annual monofilament testing is recommended for all patients with diabetes to identify feet at risk for ulceration and amputation 1
• Testing should begin at diagnosis for type 2 diabetes and 5 years after diagnosis for type 1 diabetes 1
• The monofilament test should be part of a comprehensive foot assessment that may also include vibration testing with a 128-Hz tuning fork and assessment of small-fiber function (pinprick/temperature) 1

Common Pitfalls to Avoid

• Applying the monofilament directly on calluses, scars, or ulcer sites can give false readings 1
• Allowing the patient to see where the monofilament is being applied may compromise test validity 1
• Using worn-out monofilaments that have lost their calibrated force 1
• Failing to include "mock" applications to verify patient responses 1
• Sliding the monofilament across the skin instead of applying perpendicular pressure 1