At what level of risk is preoperative natriuretic peptide (NP) and postoperative troponin testing justified in patients undergoing surgery?

Practical Thresholds for Preoperative Natriuretic Peptide and Postoperative Troponin Testing

Reserve preoperative natriuretic peptide testing for patients with ≥1 RCRI risk factor undergoing elevated-risk surgery, or any patient ≥65 years undergoing elevated-risk surgery, as these populations demonstrate sufficient baseline risk (>1% cardiac event rate) to justify testing. 1

Defining Elevated-Risk Surgery

The 2024 AHA/ACC guidelines classify elevated-risk surgery as procedures with reported cardiac risk ≥1%, which includes:

• Major vascular surgery (open aortic, peripheral arterial procedures)
• Intraperitoneal and intrathoracic procedures
• Prolonged orthopedic procedures (hip/spine surgery)
• Major head and neck cancer surgery 1

Do not order natriuretic peptides for low-risk procedures (<1% cardiac risk) regardless of patient factors, as the pretest probability is too low to justify testing. 1

Patient Risk Stratification for Testing

Test preoperative natriuretic peptides in these specific scenarios:

High-priority testing (Class IIa recommendation):

• Known coronary disease, heart failure, or structural heart disease + elevated-risk surgery 1
• Peripheral arterial disease or cerebrovascular disease + elevated-risk surgery 1
• Age ≥65 years + elevated-risk surgery 1
• RCRI score ≥1 + elevated-risk surgery 1
• Poor functional capacity (<4 METs or DASI score ≤34) + elevated-risk surgery 1

Lower-priority testing (may consider):

• ASA class ≥3 + elevated-risk surgery 1
• Perceived frailty in patients <65 years + elevated-risk surgery 1

Do NOT test natriuretic peptides in:

• Good functional capacity (≥4 METs) with no cardiac history, as these patients have NYHA class I equivalent with BNP levels typically <35 pg/mL and negligible short-term cardiac event rates 1
• Any patient undergoing low-risk surgery 1
• Asymptomatic patients with RCRI score of 0 undergoing intermediate-risk surgery (though this remains debatable) 1

Interpreting Preoperative Natriuretic Peptide Results

Critical decision thresholds:

Proceed with surgery with standard perioperative management:

• BNP <100 pg/mL or NT-proBNP <100 pg/mL: Excellent negative predictive value 1

Proceed with enhanced monitoring and consider optimization:

• BNP 100-200 pg/mL or NT-proBNP 100-300 pg/mL: Cardiac event rate approaches 5% 1
• BNP 200-300 pg/mL: 4.9% major adverse cardiac event risk, 13% total cardiac event risk 1

Strongly consider postponing elective surgery for medical optimization:

• BNP >300-400 pg/mL or NT-proBNP >400-900 pg/mL: 40% major adverse cardiac event risk, 81% total cardiac event risk 1
• These levels approach or exceed heart failure diagnostic thresholds and mandate preoperative cardiac evaluation with echocardiography 1, 2

Important confounders affecting interpretation:

• Obesity (BMI ≥30): Lower BNP by 20-30% from expected values; consider using lower thresholds (e.g., BNP >75 pg/mL instead of >100 pg/mL) 1, 2
• Advanced age (>75 years): Higher baseline values; NT-proBNP >100 pg/mL remains independently associated with mortality 1, 2
• Renal dysfunction: Decreased clearance elevates levels; interpret cautiously with creatinine >200 μmol/L 1, 3
• Atrial fibrillation: Independently elevates levels regardless of ventricular function 2

Postoperative Troponin Monitoring Strategy

Obtain postoperative troponin measurements in the same patient populations who qualified for preoperative natriuretic peptide testing, as the risk stratification criteria are identical. 1

Specific troponin monitoring protocol:

Timing of measurements:

• Obtain baseline preoperative troponin to establish reference and improve interpretation of postoperative elevations 1
• Measure troponin at 0 hours (arrival to recovery), 12 hours, and 48 hours postoperatively for patients meeting testing criteria 4, 5
• Extend to 72 hours if clinical suspicion for myocardial injury persists 4

Clinical utility:

• Preoperative troponin elevation (even without symptoms) identifies chronic myocardial injury and increases perioperative risk 57-fold 6
• Preoperative troponin improves RCRI predictive performance for perioperative MACE 1
• Postoperative troponin elevation >0.32 ng/mL defines acute myocardial injury requiring intervention 7

Practical Algorithm for Clinical Decision-Making

Step 1: Classify surgical risk (elevated vs. low)

• If low-risk surgery → No testing indicated 1

Step 2: Assess functional capacity

• If ≥4 METs with no cardiac history → No testing indicated 1
• If <4 METs or unable to assess → Proceed to Step 3

Step 3: Calculate RCRI or identify high-risk features

• If RCRI ≥1 OR age ≥65 OR known CVD → Order preoperative BNP/NT-proBNP 1
• If RCRI = 0 and age <65 and no CVD → Testing optional, consider ASA class and frailty 1

Step 4: Interpret results and act

• BNP <100: Proceed with standard care
• BNP 100-300: Enhanced monitoring, postoperative troponins
• BNP >300-400: Consider postponing elective surgery, obtain echocardiography, optimize medical therapy 1, 2

Step 5: Postoperative monitoring

• If preoperative testing was indicated → Obtain serial troponins (0,12,48 hours) 4, 5
• If postoperative NT-proBNP >860 pg/mL → High risk for cardiovascular events, intensify monitoring 1

Common Pitfalls to Avoid

• Do not order natriuretic peptides universally—the area under the curve for detecting subclinical cardiac dysfunction is <0.70, making it ineffective as a screening test in unselected populations 1
• Do not rely solely on percentage change in postoperative BNP—absolute levels matter more than relative increases (median 238-292% increase occurs regardless of events) 1
• Do not dismiss mildly elevated levels in obese patients—obesity paradoxically lowers BNP while increasing cardiovascular risk 1, 2
• Do not use BNP for monitoring patients on sacubitril/valsartan—use NT-proBNP instead as neprilysin inhibitors artificially elevate BNP 2
• Do not order testing without a plan to act on results—there is limited evidence that preoperative troponin alone changes management without accompanying clinical context 1