Firstly, the basic rules:
1. Reading Sub-test
Only use abbreviations, if they are used in the text. They may be used
- because the full term is long and complicated, e.g. DNA (deoxyribonucleic acid)
- because the abbreviation or acronym is well-known and accepted, e.g. HIV
2. Listening Sub-test
According to the OET website
'Yes, you can use abbreviations that are commonly accepted in your profession and which are clear to other professionals, for example “BP” for blood pressure. Avoid abbreviations that are specific to a particular workplace or specialism, because these might not be commonly understood. OET Assessors are trained to accept a reasonable range of abbreviations, but OET does not refer to any specific dictionaries or lists.'
3. Writing Sub-test
According to the OET website
Abbreviations that are commonly accepted in the candidate’s profession and clear to the Assessors may be used in the Writing sub-test, for example “BMI” for body mass index, or units of measurement such as “mg”. Appropriacy of language is one of the five assessment criteria for the Writing sub-test and you can find detailed information about these in the OET Preparation Support Pack.
You should also consider who the intended reader is. If your target reader is a health professional, a number of commonly used abbreviations are likely to be acceptable. However, if you are writing to somebody from a non-health professional background, full word-forms may be preferable. OET Assessors do not refer to any specific lists of abbreviations and OET does not recommend any dictionary or handbook of abbreviations.'
As mentioned, the OET does not recommend any particular list of abbreviations. Take care, when researching lists of abbreviations and pay attention to the date of release of the abbreviations. These days, abbreviations are relatively standard across English-speaking countries, however, there are slight differences between,say Australia and the UK. And, abbreviations are reviewed on a regular basis to ensure that their meaning is clear.
For example, years ago, it was possible to write 'units of insulin' as 'u'. For instance, 18u of insulin. If written quickly or with poor handwriting, 'u' can be unclear, so it is now compulsory to write the whole word, i.e. 18 units of insulin.
The acronyms IDDM (insulin-dependent diabetes mellitus) and NIDDM (non-insulin dependent diabetes mellitus) have been replaced by Type 1 and Type 2 diabetes.
Despite this, it is useful to have a list of standard and accepted abbreviations and acronyms. I have attached an example from an NHS hospital in the UK. Be aware that, even though the list is current and not due for review, until 2020, there are terms which are no longer used. For instance, terms relating to time are no longer written as 2/7, rather '2 days'.