Direct Conversion Between BNP and NT-proBNP
There is no simple 1:1 conversion between BNP 222 pg/mL and NT-proBNP because these are distinct molecules with different biological properties, clearance mechanisms, and measurement ranges that cannot be directly interchanged. 1
Why Direct Conversion Is Not Recommended
BNP and NT-proBNP are not interchangeable biomarkers - they have fundamentally different half-lives (BNP ~20 minutes vs NT-proBNP 1-2 hours), clearance mechanisms, and detection ranges (BNP 0-5,000 pg/mL vs NT-proBNP 0-35,000 pg/mL) 1, 2
BNP assays measure both BNP and proBNP together - current commercial BNP assays cross-react with uncleaved proBNP, meaning the reported "BNP" value actually represents proBNP plus BNP 3
Guidelines explicitly state these markers are not standardized - BNP assays agree at 100 ng/L and NT-proBNP assays are similar at 125 ng/L, but other measurements are method-dependent 1
Approximate Estimation Using Research Formulas
If conversion is absolutely necessary for clinical context, research studies suggest:
Using the most recent multicenter formula: log NT-proBNP = 1.21 + 1.03 × log BNP - 0.009 × BMI - 0.007 × eGFR 4
- For BNP 222 pg/mL, this would estimate NT-proBNP approximately 1,400-1,800 pg/mL (depending on patient's BMI and renal function)
- This formula showed correlation coefficient of 0.942 in validation 4
Alternative formula incorporating additional factors: Requires age, sex, BMI, creatinine clearance, hemoglobin, and atrial fibrillation status, with correlation r = 0.928 5
Clinical Interpretation of BNP 222 pg/mL
Rather than converting, interpret BNP 222 pg/mL using its own diagnostic thresholds:
This value falls in the "gray zone" (100-400 pg/mL) where heart failure is possible but not confirmed 1, 6
BNP >100 pg/mL indicates likely heart failure with increasing probability as values rise toward 400 pg/mL 6, 7
This level is elevated above normal ranges for all age groups (young adults <25 pg/mL, males 45-59 years <100 pg/mL, males >60 years <98 pg/mL) 1, 7
Prognostic significance: Each 100 pg/mL increase in BNP confers approximately 35% increased relative risk of death over 1.5-3 years 6, 7
Important Clinical Caveats
Renal dysfunction elevates both markers - if GFR <60 mL/min/1.73 m², a higher BNP cut-off of 200-225 pg/mL is recommended to rule out heart failure 1
Obesity lowers BNP values - patients with BMI >35 kg/m² may have falsely reassuring BNP levels despite cardiac dysfunction 1, 7
Other conditions elevating BNP at this level: atrial fibrillation, pulmonary embolism, sepsis, hyperthyroidism, and acute coronary syndrome 3
Serial measurements should use the same peptide - do not switch between BNP and NT-proBNP for monitoring treatment response 2
Recommended Approach
Interpret BNP 222 pg/mL as a continuous variable indicating intermediate risk, requiring echocardiography for definitive diagnosis rather than attempting conversion to NT-proBNP. 1, 6