Troponin values in the elderly

Cardiac troponin T (cTnT) is the biomarker of choice for diagnosis of acute coronary syndromes (myocardial infarction (MI) and unstable angina).

The cardiac muscle cell (myocyte) necrosis, consequent on ischemia that characterises MI, results in release of troponins from necrosed cardiac myocytes to blood and rising blood levels during the hours after onset of MI.

Peak cTnT levels occur at 2-24 hours after onset, before a gradual return to baseline 10-14 days later.

Increased cTnT is defined as one that is greater than the 99th percentile value of a healthy reference population; study has determined this value to be around 14 ng/L.

In healthy individuals, cTnT is always less than 14 ng/L and is very often undetectable (< 3 ng/L) by the most sensitive assays currently available.

A diagnosis of MI is excluded by the finding of cTnT persistently < 14 ng/L.

A recently published study of cTnT values among the elderly highlights an important limitation of the test, i.e. its lack of specificity for acute coronary syndrome.

There are many conditions other than MI and unstable angina that are associated with cardiac myocyte necrosis and consequent increase in cTnT.

The study population comprised 679 elderly hospitalised patients; mean (±SD) age was 85 ± 5.8 yrs. Crucial for the study, none had ACS, myocardial infarction or unstable angina. On the second morning of hospitalization, after an overnight fast, blood was sampled for a range of tests, including high sensitivity cTnT.

All study patients were also submitted for echocardiographic examination that allowed generation of a number of parameters related to the heart function.

Almost all (98.4 %) had detectable cTnT (> 3 ng/L) and a total of 352 (52 %) had a positive troponin result (cTnT >14 ng/L) consistent with a diagnosis of MI.

Each of the 679 study patients was assigned to one of three groups depending on their cTnT result: group 1 cTnT ≤ 10 ng/L (n=222); group 3 cTnT 11-17 ng/L (n=221); and group 3 cTnT ≥ 18 ng/L n=236).

Comparison of the characteristics of the patients in each group revealed risk factors for increased cTnT in the absence of ACS. This analysis found for example that age is independently associated with risk of increased cTnT, as is male gender.

This suggests that the usual cut-off value (14 ng/L) for diagnosis of MI is not appropriate in the elderly. Age and gender specific cut-off values need to be determined.

The study has revealed a number of other factors that are independently associated with increased cTnT in elderly patients without ACS, such as increased serum natriuretic peptide (NT-proBNP) concentration, diabetes, renal dysfunction (reduced eGFR) and echocardiographic abnormalities associated with chronic cardiovascular disease.

Clearly, the presence of chronic disease and the aging process itself pose particular challenges when using cTnT to diagnose MI in the elderly. For this group, serial measurement of cTnT and demonstration of an acute rise from baseline is vital.

Increased cTnT is, as this study has well demonstrated, not necessarily indicative of ACS.