I am writing a meta-analysis looking at the correlation between different tests for assessing body composition. 

The results of the studies that I have included use different ways to calculate the correlation, including linear regression (r squared), pearson's r, concordance correlation coefficient (CCC), and mean difference (SD) + 95% CI. 

I would like to compare these results. I have found that I can take the square root of r squared to get r. Is there also a way to calculate r from CCC? Or is CCC so similar to pearson's r, that I can just call it r and throw everything on one pile?