Baseline is sometimes 0 (eg. in successfully treated cancer patients where follow-ups are required for the specific cancer biomarkers to see if there is recurrence of the cancer )and cannot be used in
(Follow-up minus baseline)/ Baseline
For consistency when comparing baseline vs follow-ups for a patient it is best to do statistical analysis (t-test or ANOVA) to compare follow-ups with the basal group. This can also be done where baseline is high for a biomarker and then decrease upon intervention (eg. blood glucose for diabetes intervention studies).
If you just need to calculate the change in biomarkers, you can either subtract from baseline the follow-up, or vice versa. Just keep in mind that in the first case, the negative value will mean increase and positive - decrease; and vice versa for the second case. Then you may also create categories in the delta values, such as increase, small decrease, moderate decrease and big decrease, for further analyses.
It may be a bit more complicated than that since you will need to include the uncertainties of the results. This includes not only the analytical variation but also biological. There is a considerable literature on the subject beginning with the essays of Eugene Harris and James Boyd in the 1980-ies. Google for 'Reference change value' or 'Minimal difference'
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