From the Guidelines
The reference range for N-terminal pro B-type natriuretic peptide (NT-proBNP) is less than 300 pg/mL for patients under 50 years old, less than 900 pg/mL for patients between 50-75 years old, and less than 1,800 pg/mL for patients over 75 years old, as recommended by the most recent study 1. When interpreting NT-proBNP results, it's essential to consider the patient's clinical context, as values can be elevated in conditions other than heart failure, including renal dysfunction, atrial fibrillation, pulmonary embolism, and sepsis. Some key points to consider when using NT-proBNP as a diagnostic tool include:
- NT-proBNP is a cardiac biomarker released when the heart is under strain, particularly from conditions that cause ventricular stretching like heart failure.
- Levels increase with age due to declining renal function and subclinical cardiac changes.
- Obesity may cause falsely low values, and adjustment of cut-off values may be necessary in obese patients.
- NT-proBNP is particularly useful for ruling out heart failure when levels are below the reference range, as low values have a high negative predictive value. It's also important to note that the reference range may vary slightly between laboratories, and the use of NT-proBNP should be guided by the most recent and highest-quality evidence, such as the study by 1.
From the Research
Reference Range for NT proBNP
The reference range for N-terminal pro b-type natriuretic peptide (NT proBNP) in picograms per milliliter (pg/mL) is as follows:
- According to 2, the mean NT-proBNP value of patients was 9741.9 ± 8973 pg/ml (range: 245-35000 pg/mL).
- 3 states that NT-proBNP values <125 pg/mL effectively rule out left ventricular systolic dysfunction (LVSD).
- The study 3 also mentions that an age-differentiated cut-off value for NT-proBNP (125 pg/mL for <75 years old and 450 pg/mL for > or =75 years old) did not increase diagnostic performance.
Age-Related Reference Intervals
Some studies provide age-related reference intervals for NT proBNP:
- 4 reports that NT-proBNP concentrations varied greatly according to age and sex, with higher values in early childhood, relatively lower in late adolescence, and highest through middle age and older age.
- 5 observed an age-dependent increment of NT-proBNP levels with higher values in women compared to men, and reported upper reference limits (97.5% quantiles) for different age groups.
- 6 established a reference interval for NT-proBNP in elderly people, with an upper limit of < or =540 ng/L (< or =64 pmol/L).
Units of Measurement
Note that some studies report NT proBNP values in nanograms per liter (ng/L) or picomoles per liter (pmol/L), which can be converted to picograms per milliliter (pg/mL) for comparison:
- 1 ng/L is equivalent to 1 pg/mL (since 1 ng = 1 pg and 1 L = 1000 mL).
- 1 pmol/L can be converted to pg/mL using the molecular weight of NT proBNP (approximately 8.5 kDa or 8500 g/mol), but this conversion is not necessary for the reported reference ranges.