I had a similar experience, but the opposite way around, three separate things immediately sprung to mind reading your post, after many tests in UK over a "long" period of time went to AEK Udon in Thailand and had some tests before lunch and results after; High Cholesterol, took results back to UK, further test and confirmed. Following that had many aches and pains, further UK tests and nothing picked up on, back to AEK Udon and CPK/CK levels dangerously high, bad reaction to Simvastatin. Took results back to UK, as they were in USA format, 2 weeks wait after blood test and levels confirmed. Helicobacter Pyloris, confirmed as clear in the UK, but was still having issues, Thailand detected, further course of antibiotics and hey presto.
Also had a referral for a MRI scan in UK and given the all clear, when in Thailand they detected a problem with internal organ and so phoned UK hospital as had information from MRI scan, they rechecked and the organ in question had been given the all clear with a note that only 10% was visible, but the rest was obscured (think it was by bowel gas) and based on the visible 10% they gave it the all clear.
I am always sceptical about UK results On the cholesterol side, when I returned with the results they also helped out for my grandmother, as she went from being the "mystery woman" in a Somerset hospital to also being diagnosed with extremely high cholesterol, this was after many years of tests and missed diagnosis.