During the course of the IDEXX/California Animal Hospital cardiac study we have discovered a number of interesting associations. One such association is the fact that enrolled patients with masses or tumors have higher levels of troponin than similar patients with cardiac disease alone.
Taking all 658 patients currently in the study, normal dogs (n=115) have a mean troponin of 0.34 ng/ml (95% CI 0.22-0.46); those patients with at least some minor echocardiographic changes (n=445) have a mean troponin concentration of 1.29 ng/ml (95% CI 0.97-1.61) while patients with a mass or tumor (n=98) have a mean troponin of 11.71 ng/ml (95% CI 4.99-18.46). Wilcoxon tests show that the group with masses is significantly higher than both the normal dogs and the cardiac disease population (p<0.0001). Dividing the cardiac patients into those with minor echocardiographic changes or with asymptomatic disease and those with clinical signs of heart disease or heart failure gives a mean troponin of 0.79 ng/ml (95% CI 0.44-1.13) for the first group and a mean of 1.82 ng/ml (95% CI 1.29-2.36) for the second. Treating the patients with masses in the same manner so that we have a group with masses and minor echocardiographic changes or asymptomatic disease and a group with masses and clinical signs of heart disease or heart failure. The means for the two groups are 21.46 ng/ml (95% CI 6.69-36.22) and 5.12 ng/ml (95% CI 1.31-8.92) respectively. In both cases the group of patients with masses are still significantly different from the comparable cardiac group (p<0.0001 and p<0.0026); therefore severity of cardiac disease does not explain the observed difference.
The percentage of patients with a troponin over 2.00 ng/ml in the entire cardiac disease only group is about one-third of that in the group with masses. This gives a 5.4-fold relative risk that elevated troponin is associated with a mass or tumor. Dropping to a 1.00 ng/ml cut-off still gives a 3.5-fold relative risk.
The entire cardiac and masses/tumor groups are similar in terms of N-terminal prohormone atrial natriuretic peptide concentration (1943 vs. 1766 fmol/ml respectively) and N-terminal prohormone brain natriuretic peptide concentration (1482 vs. 1190 pmol/L respectively). Again indicating that the underlying cardiac disease is not the cause of the differences in troponin.
Taking into account the location of the mass it is apparent that troponin is not consistently elevated in the presence of a mass. Only masses located in the heart, spleen or in multiple locations show mean troponin levels over 1.00 ng/ml. Masses in organs such as the lung or liver do not result in a mean troponin greater than 1.00 ng/ml.
Troponin is not consistently elevated in all cases where a mass is present so it cannot be used as a tumor screen however, troponin levels above 1.00 ng/ml may indicate that the patient has a mass or tumor, and that the mass is likely located in the heart, spleen or in multiple sites.