What is ng/mL?
ng/mL (nanograms per milliliter) is a mass-based unit of concentration that expresses the amount of a substance—typically a drug, biomarker, or other analyte—present in one milliliter of fluid, where one nanogram equals one billionth of a gram (10⁻⁹ grams). 1
Clinical Context and Usage
ng/mL is the standard unit for reporting concentrations of numerous substances in clinical medicine, including:
Cardiac biomarkers: Troponin values are reported in ng/L or pg/mL (equivalent units) to diagnose myocardial infarction, with the 99th percentile upper reference limit serving as the diagnostic threshold 1
Natriuretic peptides: BNP and NT-proBNP concentrations for heart failure diagnosis are expressed in ng/L, with specific cut-points (e.g., BNP >100 ng/L suggests heart failure) 1
Anticoagulant monitoring: Dabigatran plasma concentrations are measured in ng/mL, with therapeutic ranges typically 50-400 ng/mL and safe hemostatic thresholds below 30-50 ng/mL 1
Antidepressant therapeutic drug monitoring: Plasma concentrations are reported in ng/mL with specific therapeutic windows (e.g., nortriptyline 70-170 ng/mL) 1
Tumor markers: PSA levels are measured in ng/mL, with age-specific reference ranges guiding prostate cancer screening decisions 1
Pharmaceutical compounds: Drug concentrations in biological fluids and environmental samples are routinely expressed in ng/mL or ng/L 1
Why Mass Units Rather Than Molar Units?
Mass-based units (ng/mL, mg/L) are preferred over molar units in clinical practice because drugs are prescribed and dispensed by mass, making mass concentration units more practical and safer for patient care. 2 Converting to molar units would require prescribing drugs in moles, causing significant disruption, expense, and potential danger to patients without providing meaningful clinical benefit 2, 3
Measurement Methodology
Concentrations in ng/mL are typically determined using:
High-performance liquid chromatography (HPLC) with various detectors (UV/VIS, fluorescence, electrochemical, mass spectrometry) for pharmaceutical analysis in biological fluids 4
Immunoassays for biomarkers like troponin and natriuretic peptides 1
Specialized assays such as dilute thrombin time or ecarin-based tests for anticoagulants 1
Practical Considerations
When interpreting ng/mL values, clinicians must account for factors that affect concentrations, including:
- Patient-specific variables (age, renal function, body mass index) that alter reference ranges 1
- Assay-specific characteristics, particularly precision (coefficient of variation) at clinically relevant thresholds 1
- Sample stability and handling requirements, as some compounds degrade rapidly in biological matrices 1
The unit provides a standardized, internationally recognized method for quantifying trace amounts of substances in clinical specimens, enabling consistent interpretation across laboratories and healthcare settings 1, 2.