Sample stability:
-
24 hours at 2-8 o C
-
12 months at -20 o C
Reference Intervals
Units
Infants
see
"Troponin T and Troponin I in Children"
below
Adults
< 15
ng/L
Uncertainty of measurement: 8% at the level of 16 ng/L
6% at levels of 100 ng/L and higher
Urgent result, 1 hour turnaround time
Principle: Sandwich type immunoassay with chemiluminescence detection
Reagents: Roche Troponin T hs kit
Analyser: Cobas e801
A raised troponin T level indicates myocardial damage, of which there are many causes. The reference range is based on the 99th centile found in a healthy group of subjects.
Myocardial infarction:
An elevated troponin is not specific for myocardial infarction.
Therefore it is crucial to use the test in a way that maximises clinical specificity for myocardial infarction. The first principle is that the test should be ordered only in clinical circumstances which are consistent with acute myocardial ischaemia.
To fulfil the definition for diagnosis of myocardial infarction there must be a change in hsTnT demonstrated over time. I nfarction cannot be ruled out until a negative troponin is obtained at 9-12 hours after onset of symptoms.
To avoid over-interpretation of changes which may reflect only normal biological and analytical variability, the following criteria are suggested:
-
Between 15 and 50 ng/L the change should be at least 50%.
-
At levels above 50 ng/L the change should be at least 20%.
Troponin T levels may remain elevated for up to 10 days after MI.
Conditions other than coronary artery disease which can caused elevated troponin:
-
myocarditis, cardiomyopathy, drug toxicity (e.g. chemotherapy)
-
demand ischaemia (myocardial ischaemia not due to coronary artery disease): septic shock, hypotension, hypovolaemia, SVT/atrial fibrillation, LV hypertrophy.
-
myocardial strain: cardiac failure, pulmonary embolism, pulmonary hypertension
-
cardiac trauma, contusion or cardioversion
-
renal failure: t roponins are frequently persistently elevated in patients with end-stage renal disease. Decreased clearance may partly explain this, but other factors (e.g. clinically silent myocardial necrosis) have also been proposed. However, elevated troponin is associated with a worse prognosis across the whole spectrum of renal failure.
-
Skeletal Muscle disorders e.g. polymyositis and Duchenne muscular dystrophy. Skeletal muscle troponin is not detected by the troponin T assay; a raised level indicates myocardial involvement.
-
Assay interferences: Very rarely, heterophile antibodies or other causes may result in a falsely elevated result. If in doubt troponin I can be tested in another laboratory. CK may be useful to confirm myocardial damage.
Falsely low results due to haemolysis:
Haemolyzed samples may show results up to 50% lower than the true level.
Troponin T and Troponin I in Children:
Troponin T in healthy infants may be much higher than in adults. After an initial peak around the first month of life, troponin T levels have been observed to decrease to adult levels around 6 - 12 months of age (Yang Q, Zhou Y, Zhang S et al. 2021. Establishment of the reference interval for high-sensitivity cardiac troponin T in healthy children of Chongqing Nan'an district . Scandinavian Journal of Clinical and Laboratory Investigation, 81(7): 579-84). Troponin T results for infants should be interpreted with caution as reference limits are not well established in this age group.
Similarly, troponin I is also higher in healthy infants than in adults. We expect to see the highest levels around 1 month of age and troponin I comes down over the first 6 - 12 months of life. It is also affected by acute illness, prematurity and asphyxia. Because there are several different methods of measuring troponin I, there can be significant differences in the exact concentrations of troponin I measured, however the overall pattern remains the same.
Emails to chemicalpathologist@adhb.govt.nz will receive priority attention from the on-call chemical pathologist.
If the query concerns a specific patient please include the NHI number in your email.
If email is not a suitable option, please contact the on-call chemical pathologist via Lablink (Auckland City Hospital ext. 22000 or 09-3078995).
Individual chemical pathologists may be contacted but will not be available at all times.
After-hours : contact Lablink (Auckland City Hospital ext. 22000 or 09-3078995) or hospital operator for on duty staff after hours.
Dr Samarina Musaad (Clinical Lead) : SamarinaM@adhb.govt.nz ext. 22402
Dr Cam Kyle: CampbellK@adhb.govt.nz ext 22052
Dr Weldon Chiu: WeldonC@adhb.govt.nz ext. 23427
Dr Campbell Heron: CHeron@adhb.govt.nz ext. 23427