Monofilament Test in Diabetes
Primary Purpose
The 10-g monofilament test is used to identify loss of protective sensation (LOPS) in patients with diabetes, which indicates those at high risk for foot ulceration and amputation. 1
Screening Indications
- All patients with type 2 diabetes should undergo annual 10-g monofilament testing starting at diagnosis 1
- Patients with type 1 diabetes should begin annual testing 5 years after diagnosis 1
- Testing should continue at least annually thereafter for all patients with diabetes 1
What the Test Detects
The monofilament specifically assesses large-fiber function and protective sensation, not early neuropathy. 1 This is a critical distinction—the test is designed to identify patients who have already lost the ability to feel pressure that would normally protect them from injury, rather than detecting subtle early nerve damage. 1
Absent monofilament sensation indicates LOPS, which is a major risk factor for diabetic foot ulceration and subsequent amputation. 1
Proper Testing Protocol
The 10-g monofilament should ideally be performed with at least one additional assessment to improve diagnostic accuracy: 1
- Pinprick sensation (small-fiber function) 1
- Temperature sensation (small-fiber function) 1
- Vibration perception using a 128-Hz tuning fork (large-fiber function) 1
- Ankle reflexes 1
Interpretation algorithm: At least two normal tests with no abnormal tests rules out LOPS, while absent monofilament sensation suggests LOPS. 1
Testing Sites
While guidelines recommend the test be performed, research shows that testing at 3-4 sites provides similar sensitivity and specificity to testing at 8-10 sites (sensitivity 35.9-53.8% vs 38.5-64.1%; specificity 73.9-87.4% vs 64-95.5%). 2 The two-site approach (third and fifth metatarsal head sites) demonstrates 93% sensitivity and 100% specificity for detecting diabetic peripheral neuropathy. 3
Clinical Significance for Risk Stratification
The monofilament test results directly inform risk stratification: 4
- Very low risk: No LOPS and no peripheral arterial disease
- High risk: LOPS or peripheral arterial disease with history of foot ulcer, amputation, or end-stage renal disease 4
Patients identified with LOPS require immediate education on daily foot inspection, proper footwear selection, and regular podiatry follow-up. 4, 5
Important Limitations
The 10-g monofilament is not sensitive enough for detecting early neuropathy—it identifies severe neuropathy and those at increased risk of ulceration. 6 Environmental conditions and testing technique can affect accuracy, requiring standardized protocols. 6 The test should be combined with other assessments rather than used in isolation for optimal diagnostic accuracy. 1