More important than blood values, for me, is that all professional athletes should be made to declare any TUE ("Therapeutic Usage Exemptions") they have been given.
For example, just looking at the "Athletics Weekly" forums (which are generally quite balanced and factual, unlike some other athletics forums - not "Runner's World" I might add !) there seems to be an unexpectedly high number of athletes, swimmers and cyclists who are - legally - taking asthma medications. There also seem to be many being treated for thyroid deficiencies.
While this is all perfectly legal (those athletes named have been prescribed their usage as "TUE's") a quick Google search of for example "Predisnone endurance" (one of the named asthma meds prescribed to a very famous cyclist, allegedly) shows why this should be a cause for concern. The effect on amateur runners and cyclists of even short-term usage seems to be quite extraordinary, so one can only imagine what effect controlled, long-term usage must have on a professional endurance athlete.
Unfortunately, the public image of athletics and cycling means that any exceptional performance is immediately questioned.
Recent examples - G Dibaba's 1500 m world record last week (breaking a record set by one of "Ma's army" that was thought to be unbreakable) and Chris Froome's stunning uphill stage win the TdF.
On the one hand with the vastly more effective testing and scrutiny nowadays, it seems hard to believe that anyone would take the risk.
On the other, twice-convicted Justin Gatlin is running faster "clean" at 33 than he was when he was found to be breaking the rules (and in an event where you would expect someone to be well past their best by that age), so no wonder people are confused.
I got hooked on athletics ( and cycling, and other sports) in an era when boundaries and records were being continuously pushed forward - and that was the whole essence of the sport. With the benefit of hindsight, lots of those records (Marlies Goer, Flo Jo, Randy Barnes, Daniel Komen etc) would be immediately suspected nowadays (in some cases, with good reason).
I guess those of us who aren't "on the inside" will never know.
The one thing I've never been comfortable with is Mo's UK 1500 metres record. Taking 5 seconds off your PB at age 30 and running faster than Coe, Cram or Ovett ever did - 3 MD specialists and acknowledged all-time greats ...?