What are the units and normal ranges for troponin I (Troponin I) tests?

Troponin I Units and Normal Ranges

Troponin I is measured in nanograms per liter (ng/L) or nanograms per milliliter (ng/mL), with normal ranges varying by assay type, with high-sensitivity assays having lower cutoff values than conventional assays. 1

Units of Measurement

• Troponin I is typically measured in nanograms per milliliter (ng/mL) or nanograms per liter (ng/L) 1
• 1 ng/mL = 1 μg/L = 1000 ng/L (unit conversion) 1
• Some literature may use micrograms per liter (μg/L), which is equivalent to ng/mL 1

Normal Ranges

Conventional Troponin I Assays

• Normal values are typically below 0.03-0.05 ng/mL (30-50 ng/L) 2, 3
• The 99th percentile upper reference limit (URL) varies by manufacturer but generally ranges from:
  • 0.03-0.10 ng/mL for most conventional assays 4, 3
  • Values above the 99th percentile are considered abnormal and may indicate myocardial injury 5, 4

High-Sensitivity Troponin I Assays

• Normal ranges are significantly lower than conventional assays 1
• For Abbott ARCHITECT high-sensitivity troponin I assay:
  • Women: <16 ng/L (<0.016 ng/mL)
  • Men: <34 ng/L (<0.034 ng/mL) 1
• The limit of detection (LoD) for high-sensitivity assays can be as low as 1.2-5 ng/L 1
• The limit of quantification (LoQ) is approximately 6 ng/L for high-sensitivity troponin T assays 1

Clinical Decision Points

• For acute coronary syndromes, different cutoffs are used depending on the clinical protocol:
  • Rule-out criteria for high-sensitivity troponin I: <5-6 ng/L at presentation or <26 ng/L at 0 and 3 hours 1
  • Rule-in criteria for high-sensitivity troponin I: >64 ng/L at presentation or delta change of ≥15 ng/L at 2 hours 1
• For conventional assays, a cutoff of 0.4 ng/mL has been associated with increased mortality risk in acute coronary syndromes 5
• In pulmonary embolism studies, various cutoffs have been used ranging from 0.03-0.5 ng/mL to assess risk 1

Important Considerations

• Laboratory-specific reference ranges should always be consulted as they vary by assay manufacturer and methodology 1
• The National Academy of Clinical Biochemistry recommends setting the upper limit of normal at the 99th percentile for the normal healthy population 1
• Point-of-care troponin assays may have different sensitivity compared to laboratory-based tests, with some studies suggesting using 50% of the 99th percentile as cutoff to improve sensitivity 6
• Even troponin elevations below the diagnostic cutoff for myocardial infarction may have prognostic significance 3
• Non-ACS causes of troponin elevation typically have lower levels (median 0.14 ng/mL) compared to STEMI (median 10.2 ng/mL) or NSTEMI (median 0.4 ng/mL) 4

Always refer to the specific reference ranges provided by your laboratory, as values can vary significantly between different assay methods and manufacturers.