Regarding the 93 year old lady with positive CK and CK MB and the CK-MB
index >5% (100 x CK-MB mass on AxSYM / total CK activity on Vitros, (we use
the same intruments)) but normal TnT and TnI: The concordant negative
troponin results make cardiac damage unlikely. While interference in the
CK-MB assay is possible, the concordant fall of CK-MB with total CK
suggests release from another source rather than assay interference. Some
patients have elevated amounts of CK MB in skeletal muscle (although 10%
would be very rare). I will be interested to see what the CK-MB index is
when the insult has passed, as it ususally remains elevated in these
patients.
Graham Jones
Staff Specialist in Chemical Pathology
St Vincent's Hospital Sydney
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