If you are just starting the process for next year - you will have to declare the diagnosis.
Why does the OP have to declare the diagnosis? High cholesterol is not on the list of disqualifying conditions.
Also, only a physician can make an official diagnosis.
"MEDICAL STANDARDS. Throughout this enclosure, ICD, CPT and HCPCS codes are
included with most medical conditions and procedures, usually parenthetically, to aid cross-
referencing. Unless otherwise stipulated, the conditions listed in this enclosure are those that do
NOT meet the standard
by virtue of current diagnosis, or for which the candidate has a verified
past medical history. The medical standards for appointment, enlistment, or induction into the
Military Services are classified by the general systems described in sections 3-3031 of this
enclosure."
I'm not sure how blood test readings work, but if a physician never diagnosed the OP with high cholesterol, the OP has not been officially diagnosed with high cholesterol nor does he have a verified past medical history, and under those circumstances, the instructions do not state anywhere that he must report the condition.