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|Test Update Information||Effective 12/16/2014, the platform used for the troponin assay has changed from the Abbott Architect i1000 to the Beckman Coulter DxI 600 platform. Troponin values in the range of 1.0 micrograms/L and above will read approximately 10 to 35% lower than in the past. This assay change does not affect the normal range cutoff of <0.05 micrograms/L.|
|Performed by||Parnassus Chemistry|
|In House Availability||Test available 24 hours per day 7 days per week|
|Method||Chemiluminescent immunoassay (Beckman Coulter DxI 600)|
|Container type||Light Green top preferred; Red top or Gold top acceptable
Note: Plasma and serum samples should not be used interchangeably in the same patient
|Amount to Collect||2 mL blood|
|Sample type||Heparinized plasma or serum|
|Preferred volume||1 mL plasma or serum|
|Min. Volume||0.5 mL plasma or serum|
|Processing notes||Refrigerate plasma or serum|
|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 Beckman Coulter DxI600 platform. The 99 percentile normal cutoff for this assay in subjects between 18 - 70 years of age has been estimated to be between 0.01 and 0.04 micrograms/L (Moretti et al, Ann Clin Biochem, 2014; Gaze et al, Clinical Chemistry, abstract B354, page S262, 2014). Testing of 28 male and 29 female healthy lab volunteers at UCSF showed all results were <0.05 micrograms/L except for one subject and > 90% were below the assay limit of detection of 0.02 micrograms/L. Based on these observations, troponin I results that exceed 0.04 micrograms/L in this assay are flagged as abnormal.
The coefficient of variation of the Beckman Coulter DxI assay at a level of 0.03 micrograms/L is ~ 10% which has been confirmed by in house testing. 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.
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 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.
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.
|Last Updated||12/14/2014 12:48:21 PM|
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