Q: Can I start a sentence with an abbreviated form?

The norm is to not begin a sentence with an abbreviation, except if it’s an acronym such as NASA. The rationale for this is that it may look odd right at the beginning of a sentence, especially if it’s not all in uppercase (as in the case of ‘sF’). Additionally, some abbreviations have a period at the end, such as ‘Fig.’ for ‘figure.’ This means that these abbreviations when used at the start of a sentence will have periods right before and after, which could be confusing to read. So, you will need to indeed spell out the term when using it at the beginning of a sentence. Incidentally, if you are asking only about ‘serum ferritin,’ from the few papers we have seen, it seems to be written in full form throughout. Finally, the journal would have its own guidelines that you need to refer to, although most journals also insist on expanding the term at the beginning of a sentence.

Related resources:

• Scientific writing: Avoid starting sentences with a number or abbreviation
• Common errors in the usage of abbreviations in scientific writing
• Is it acceptable to use abbreviations in an abstract?