Biomarker ratios

The papers I’ve seen (e.g. the classic Richard Kronmal paper) relate to specific statistical modeling issues / assumption violations. In terms of pure measurement issues, ratios can work, if you can show that an ultimate outcome can be modeled as y = f(log(r)) + g(d) + h(n) for ratio r with all denominator d coefficients and all numerator n coefficients equal to zero. This takes a lot of luck. Quite often transformations of the numerator or denominator need to be taken before computing the ratio. Sometimes the transformation is just a change of origin (subtraction) in the denominator.