We use the ROCHE ELECSYS method for TnT.
We asked our phlebotomists to collect a heparin PST (Vacutainer) along with
the usual SST tube from the patients in our CCU for a week (and our thanks
go to the medical staff for allowing this access to their patients). The
results in the table below show that we find lower levels in plasma than in
sera. Sera which gave a positive result (column a) were repeated (column b)
along with the plasma (column c) to eliminate any time delay effect.
Although the differences are less than the 15% quoted below, they are in
broad agreement with the finding that plasma TnT levels are lower than serum
and will continue to recommend that only serum be used.
I'm not certain if it would stand up to a controlled trial, but as is so
often the case, showing an interest in any condition seems to have the
immediate effect of reducing the frequency of the condition. We've never
had a week with so few raised TnT levels from our CCU.
Initial Serum TnT result Repeat serum TnT Plasma TnT % difference
3.20 2.89
9.7
1.62 1.62 1.48
8.6
1.27 1.27 1.19
6.3
0.014 0.015 <0.01
0.788 0.801 0.769
4.0
0.037 0.039 0.037
0.5
JE Hogg, N Jiwani, E Simpson
Monklands Hospital,
Airdrie, UK
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Subject: Heparin & Troponin
The paper by Gerhardt, et al. in this month's Clinical Chemistry (46:817)
reports on the false decreases in TnT (Elecsys) and TnI (Immulite) using
heparin plasma compared to serum (average about 15% but up to 30% or so in
some samples). When introducing TnI on Stratus about 8 years ago and when
switching to TnI on AxSYM a few years ago, we found no significant
difference between serum and heparin plasma (although we may not have looked
as carefully as in this paper). Does anyone have other data that conflicts
with this report of false decreases in TnI or TnT on heparinized plasma
samples compared to serum?
James J Miller, Ph.D., DABCC
Associate Professor
Dept. of Pathology & Laboratory Medicine
University of Louisville
Louisville, KY 40292
502-852-1179
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