Asila,
My understanding of where we are is based on two documents.
1. The Universal Definition of myocardial Infarction (UDMI) (Journal of the American College of Cardiology 50: 2173–95). http://content.onlinejacc.org/cgi/reprint/50/22/2173.pdf:
2. NICE clinical guideline 95. Chest pain of recent onset: assessment and diagnosis of recent onset chest pain or discomfort of suspected cardiac origin, March 2010,
http://guidance.nice.org.uk/CG95
Both are more or less identical except for timings, see below:
A. Universal definition of MI
When diagnosing MI, use the universal definition of myocardial infarction. (UDMI and NICE). This is:
The detection of a rise and/or fall of Troponin T with at least one value above the 99th percentile of the upper reference limit, together with evidence of myocardial ischaemia with at least one of the following:
• symptoms of ischaemia
• ECG changes indicative of new ischaemia (new ST-T changes or new LBBB)
• development of pathological Q wave changes in the ECG
• imaging evidence of new loss of viable myocardium or new regional wall motion abnormality
B. Use of Biochemical Markers for Diagnosis of Acute Coronary Syndrome
B1. Troponin: The marker of choice is Troponin (UDMI, NICE).
B2. Timing of sampling: two Troponin T levels need to be taken (UDMI, NICE). First sample: on admission (UDMI, NICE), Second sample:10–12 hours after the onset of symptoms (NICE)
Note: UDMI recommended that the second sample should be taken at 6-9 hours post admission, however NICE recommend 10-12 hours post onset of symptoms.
B3. Interpretation: A rise or fall in the second Troponin T of at least 20% is considered a positive result (UDMI, NICE).
My interpretation is:
I will be reporting Troponin T in ng/L with a detection limit (and 99th percentile) of 14 ng/L.
We will use two samples, admission and 10-12 hours post onset of symptoms
We will use the 20% change to indicate a significant change.
I know that in parts of New Zealand (Professor Harvey White, one of the authors of UDMI) they use a different protocol. They use admission and 3 hours post admission, initially.
If admission is less than 14 they retest 6-12 hours later
If admission is ≥ 14 - < 53 ng/L they look for a 50% change at 3 hours post admission to diagnose NSTEMI
If admission is > 53 ng/L they look for a 20% change at 3 hours post admission to diagnose NSTEMI
If the change is less than 50% or 20% (as above) they retest at 6 and 12 hours post admission.
Thus, to answer your question, the 99th percentile is 14 ng/L (0.014 microg/L) and should be used to indicate elevation. But a second sample with increment greater than 20% is required to diagnose (with clinical symptoms etc) NSTEMI. The 14- 53 ng/L (0.014 to 0.053 microg/L) range has been introduced at the low end so that a greater change must be observed at the low end to indicate NSTEMI, but this only applies if you want to make a diagnosis at 3 hours post admission. The protocol makes sense as some patients can be diagnosed earlier if they have a significant increment, but if they do not have a significant increment then other samples are required.
I have gone with UDMI and NICE, and await the evidence for earlier diagnosis, with appropriate cut-offs.
Best wishes
Martin
-----Original Message-----
From: Clinical biochemistry discussion list [mailto:[log in to unmask]] On Behalf Of Asila Al-Musheifri
Sent: 01 May 2010 11:38
To: [log in to unmask]
Subject: Cut-off value for hs cTnT
Hi everyone,
Soon we will start using high sensitive cTnT in our lab. I am wondering if anyone uses the recommended cut-off value from Roche or 2 cut-off values ??. I need an expert opinion in this issue as I read that we can use one cut-off value (0.014 µg/L = 99th percentile), or 2 cut-off values (0.014 µg/L and 0.053 µg/L).
Thanks,
Asila Al-Musheifri
Chemical pathology
Oman
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