MET Levels for Preoperative Functional Status Assessment
The critical threshold for preoperative functional capacity assessment is 4 METs—patients unable to perform activities requiring 4 METs are at significantly increased risk for perioperative cardiac complications and should undergo further risk stratification. 1
MET Classification System
Functional capacity is categorized into five levels based on metabolic equivalents 1:
- Excellent: >10 METs
- Good: 7-10 METs
- Moderate: 4-6 METs
- Poor: <4 METs
- Unknown: Cannot be determined
Activities Below 4 METs (Poor Functional Capacity)
Patients who can only perform these activities are at increased perioperative risk 1:
- Slow ballroom dancing 1
- Golfing with a cart 1
- Playing a musical instrument 1
- Walking at 2-3 mph on level ground 1
- Light housework (dusting, washing dishes) - 2.70 METs 1
- Walking indoors around the house - 1.75 METs 1
- Self-care activities (eating, dressing, bathing) - 2.75 METs 1
Activities at or Above 4 METs (Adequate Functional Capacity)
Patients who can perform these activities have acceptable functional reserve for most surgeries 1:
- Climbing one flight of stairs or walking up a hill - 5.50 METs 1
- Walking 4 blocks on level ground 1
- Walking on level ground at 4 mph 1
- Heavy housework (scrubbing floors, moving furniture) - 8.00 METs 1
- Moderate housework (vacuuming, carrying groceries) - 3.50 METs 1
- Yardwork (raking leaves, pushing power mower) - 4.50 METs 1
Activities Requiring >4 METs
These activities indicate good-to-excellent functional capacity 1:
- Moderate cycling 1
- Climbing hills 1
- Ice skating or rollerblading 1
- Skiing 1
- Singles tennis 1
- Jogging 1
- Running a short distance - 8.00 METs 1
- Sexual relations - 5.25 METs 1
- Moderate recreational activities (golf without cart, bowling, doubles tennis) - 6.00 METs 1
- Strenuous sports (swimming, basketball, football) - 7.50 METs 1
Clinical Application: The Two-Question Screen
The most practical bedside assessment asks two standardized questions 1, 2:
- Can you walk 4 blocks without stopping?
- Can you climb 2 flights of stairs without stopping?
Inability to perform either activity identifies patients with poor functional capacity (<4 METs) who have significantly increased risk of perioperative myocardial ischemia and cardiovascular events (P=0.006 for blocks walked; P=0.01 for stairs climbed) 1, 2. This simple assessment is more reliable than unstructured clinical interviews 3, 4.
Structured Assessment Tools
For more precise evaluation, use the Duke Activity Status Index (DASI), which assigns specific MET values to 12 activities ranging from self-care (2.75 METs) to strenuous sports (7.50 METs) 1, 2. The DASI has demonstrated superior predictive value compared to subjective clinical assessment for identifying patients at risk of death or myocardial infarction within 30 days of surgery 4.
Important Caveats
Subjective clinical assessment of functional capacity by physicians has poor accuracy (19.2% sensitivity, 94.7% specificity for identifying inability to attain 4 METs) and should not be used alone for preoperative risk evaluation 4. The European Society of Cardiology notes that poor functional capacity has stronger prognostic value for thoracic surgery (relative risk 18.7) compared to other non-cardiac surgeries (relative risk 0.47), reflecting the importance of pulmonary function in thoracic procedures 1.
Patients with good functional capacity (≥4 METs) who are asymptomatic can typically proceed to surgery without further cardiovascular testing, as management is rarely changed by additional testing in this population 1.