82. What blood test can help distinguish between restrictive cardiomyopathy and constrictive pericarditis?

Measuring the BNP level (b-type natriuretic peptide) can help distinguish these two entities which have historically been quite difficult to diagnosis.

In constrictive pericarditis the BNP level is normal to very minimally elevated while in restrictive cardiomyopathy the BNP level is significantly elevated. This was initially described by Leya et. al. in 2005. BNP is released in response to myocardial wall stretch. In constrictive pericarditis, the scarred pericardium probits wall stretch and thus the levels are low. In restrictive cardiomyopathy, the walls indeed do stretch from the increased cardiac pressures resulting in high serum levels of BNP.