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Lab Manual for Moffitt-Long and Mount Zion

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Troponin I

Item Value
Test Update Information Effective 02/27/2013, the platform used for the troponin assay has changed from the Abbott Axsym to the Abbott Architect i1000 platform. This assay change has little or no effect on the assay results.
Approval req'd? No
Available Stat? Yes
Test code TRPI
Test group Troponin
Performed by Parnassus Chemistry
In House Availability Test available 24 hours per day 7 days per week
Method Immunochemiluminometric assay (Abbott Architect i1000)
Container type Light Green top
Amount to Collect 2 mL blood
Sample type Heparinized plasma
Preferred volume 1 mL plasma
Min. Volume 0.5 mL plasma
Processing notes Refrigerate plasma.
Units µg/L
Normal range < 0.05 µg/L
Critical value ≥ 0.05 µg/L. Note: The first elevated troponin for a patient will be called. Subsequent elevated Troponin levels for the same patient in the next 72 hours after the initial report will not be called.
Stability Room temperature 8 hours, refrigerated 3 days hours, frozen 1 month
Turn around times STAT 1 hour, Routine 4 hours
Additional information WARNING: Results from the Parnassus central laboratory troponin assay cannot be directly compared to results from the iSTAT point of care troponin assay performed at Mt Zion because of assay differences in standardization, normal cutoffs, and absolute values.

The troponin I method used in the central laboratory at Parnassus is performed on the Abbott Architect i1000 platform. In the Abbott Architect assay, the 99th percentile in normals has been reported to be in the range of 0.012 to 0.04 micrograms/L (Clinica Chimica Acta 411:1095-1101, 2010 and Clinical Chemistry Laboratory Medicine 50:791-806, 2012). A 99 percentile cutoff of 0.04 micrograms/L was verified in the Parnassus Laboratory by testing a sample of 226 apparently healthy blood donors. All troponin I results that exceed 0.04 micrograms/L in this assay are flagged as abnormal. The clinical performance characteristics of this threshold cutoff in patients with suspected acute coronary syndrome has been described by Mills et al (JAMA 305:1210-1216, 2011). Increased troponin I is a very sensitive indicator of recent cardiac injury but does not indicate the cause of the cardiac injury; many clinical conditions can cause elevations in troponin I besides just myocardial infarction.

The coefficient of variation of the Abbott Architect assay at a level of 0.05 micrograms/L has been reported to be approximately 10% or less and has been confirmed by in house testing (JAMA 305:1210-1216, 2011 and Clinica Chimica Acta 413:1786-1791, 2012). This assay is not considered a high sensitivity troponin assay and is not capable of measuring the extremely low levels of troponin that circulate in most normal subjects. Serial sampling is strongly recommended to help guide interpretation of troponin results and detect the temporal rise and fall of troponin levels characteristic of acute cardiac injury. Technical artifacts should be suspected in patients in whom an increased troponin level abruptly falls to normal much more quickly than would be expected, or in whom serial troponin levels are chronically elevated. Questionable results should be checked by repeating the assay after the sample has been carefully examined or respun as necessary to insure absence of possible fibrin strains or particulate material that could interfere in the assay. Repeat testing with a different troponin assay may be useful in cases where interference by heterophile antibodies or other immunoglobulins is suspected.

When following patients with troponin levels of < 0.25 micrograms/L, one can be confident (> 95%) that a change in results greater than ~0.02 micrograms/L is clinically real and not likely due to inherent variability in the assay (assuming use of fresh plasma samples without residual fibrin strands or interfering material). Changes of 0.01 - 0.02 micrograms/L could represent inherent assay variability or be clinically real. When following a patient with a troponin level of 0.25 micrograms/L or more, one can be confident that a change in results of greater than 10% is clinically real and not likely due to assay variability (Clinica Chimica Acta 413:1786-1791, 2012). In a patient with a troponin level of 0.25 micrograms/L or more, a change in results of 1% - 10% could represent inherent assay variability or be clinically real.

Approximately 20% - 30% of renal failure patients on dialysis have been reported to show an elevated troponin I above 0.04 micrograms/L in an Abbott Architect assay (Ann Clin Biochem 2007; 44: 285–289). Troponin I is believed to be predominantly cleared by non-renal mechanisms and increased troponin I levels in renal failure patients may signify underlying cardiac damage (Ann Clin Biochem 2007; 44: 285–289). Renal failure patients with increased troponin I levels have been reported to be at greater cardiovascular risk than those with normal levels of troponin I (Ann Clin Biochem 2007; 44: 285–289).

Note: Spurious increases in troponin I can occur in samples that contain microclots/fibrin strands. Collection of a heparinized blood specimen is recommended to minimize the chance of microclot formation. Heterophile antibodies or other abnormal immunoglobulins may cause falsely increased or falsely decreased results; falsely low results may occur in patients with autoantibodies against cardiac troponins. Technical artifacts should be suspected in patients in whom an increased troponin level abruptly falls to normal much more quickly than would be expected, or in whom serial troponin levels are chronically elevated. If a spurious result is suspected, the laboratory can be notified to repeat the result using the same assay and/or a different troponin assay for confirmatory purposes.
CPT coding 84484
LOINC code 42757-5
Last Updated 2/25/2013 12:01:33 PM
Entry Number 952
Lab Procedure Link Click here for Procedure
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