TROPONIN ASSAY CHANGE IN METHOD
The recent introduction of Troponin assays as the preferred biochemical marker of myocardial damage is based on their high sensitivity and specificity, allowing detection of myocardial injury or infarction in acute coronary syndromes within 3-6 hours [maybe up to 10 hours] of onset of symptoms remaining elevated for up to 5-10 days.Troponin I and T assays are commercially available, they provide essentially equal diagnostic utility for the detection of myocardial damage in most clinical situations. Several Troponin I assays are available, however there being no agreed international standard calibration quantitative results and quoted clinical values differ between methods.An upgrade in our immunoassay analyser necessitated a change to AXSYM Troponin I method. Close monitoring of results [including direct comparison of patient’s samples with other methods], correlation with clinical outcomes in some cases and literature review has indicated an increased number of presumed false positive elevations of Troponin I levels with this assay, particularly at low levels [0.5 – 2.0 ?g/L]. Possible analytical interferences include heterophile antibodies, rheumatoid factor, fibrin/ platelets.As a result of these concerns and considering local instrument platforms available, we have decided to change our Troponin method to the latest generation Troponin T assay [Roche], as of the 1st September 2003.ELEVATION OF TROPONIN T may be seen in:
- Acute coronary syndromes.- Non-coronary heart disease such as pericarditis, myocardial trauma, myocarditis, Congestive Cardiac Failure [CCF], pulmonary embolism, arrhythmia.- Chronic renal failure [including those on dialysis treatment] – this may represent uraemic myocarditis or coronary artery disease. Elevated levels in these patients have shown to be a poor prognostic factor for survival.- Rhabdomyolysis polymyositis.
Suggested Clinical Values For Troponin T
Normal < 0.03ug/L Myocardial Infarction >= 0.10ug/L
Values between these two levels indicate myocardial injury
SAMPLE REQUIREMENT: 5ml Gold Top with Gel [Heparin Tube is unsuitable]
TROPONIN T INTERPRETATION- Interpretation requires full clinical and ECG evaluation be available to supplement the biochemical result. A negative or normal Troponin T level does not exclude myocardial injury / infarction if the sample is taken too early for a rise to be demonstrated.- Serial testing may be required to demonstrate temporal rise and fall characteristic of acute myocardial infarction.- Discrepant results should be verified by other markers [such as CK, alternative Troponin assay].- Troponin I and T quoted clinical values and quantitative results differ. Please address comments or queries to Dr John Roberts or Mr John Dodos [Biochemistry] on 63 34 3636.
3.5 ml BLUE SODIUM CITRATE TUBE – COAGULATION
The blue sodium citrate tubes need to be filled to the fill line marked on the tube label to enable accurate INR and other coagulation studies to be performed at the laboratory. It is sometimes difficult to fill these tubes when using the vacutainer system. We suggest that needle and syringe be used for these sample collections.
ANTE-NATAL SCREENING
When patients are given Anti-D and referred for antibody screens during their pregnancy it would be appreciated if this information could be clearly stated on the request form.
DOMICILIARY VISITS
The laboratory specimen collectors are under increasing pressure to meet the demand for domiciliary visits for pathology sample collection. It would be gratefully appreciated if this service could be restricted for those patients that are unable to attend the laboratory. For those patients that do require domiciliary visits the laboratory needs to be notified, no later than the previous day unless the pathology tests are URGENT.
If you require any further assistance, please contact Mr John Millwood, Practice Manager on 63 34 3636.