David Burgess asked if CKMB mass assays could be affected by Macro-CK.
Mohammad Al-Jubouri and Paul Collinson replied no. I agree that
Macro-CK due to mitochondrial CK (type 2) almost certainly would not be
detected in CKMB mass assays.
In the case of Macro-CK due to immune complexes (type 1) there are some
ways testing for MI could be compromised. If the endogenous CK
antibodies bind CKMB and do not interfere with the binding of the two
reagent antibodies, then CKMB mass measurements should be accurate. On
the other hand and more likely, if the endogenous antibodies bound to
CKMB block (or decrease the affinity of) either reagent antibody, then
the amount of CKMB mass measured will be decreased. (Of course, that is
irrelevant if the true concentration is zero or low.)
In addition, even if the CKMB can be measured accurately (the less
likely case), the concentration may be higher than the upper limit of
normal due to slow clearance rather than MI. Also, if you use the CKMB
Index, total CK activity may be high due to slow clearance and the CKMB
Index would be decreased.
Thus, Macro-CK Type 1 may cause false negatives for detecting MI, not
false positives as in the immunoinhibition assays. And false negatives
are worse than false positives! -Jim
James J Miller, Ph.D., DABCC, FACB
Associate Professor, Pathology & Laboratory Medicine
University of Louisville, Louisville, KY 40292
Director of Clinical Chemistry & Toxicology
University of Louisville Hospital Laboratory
[log in to unmask]
Office: 502-852-1179
Pager: 502-478-1219
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