IGCSE marks the end of a stage, not the end of school. It is taken around age sixteen and is followed by A Level or the IB Diploma. Treating it as a leaving qualification is the most frequent misunderstanding in Turkey.
Why it is not a university route
Entry to a university, in Turkey or abroad, is built on a school leaving diploma. IGCSE sits two years earlier in the sequence, so it cannot fill that role however strong the grades are.
What it does is determine which A Level or IB subjects are open, and that choice then shapes the university application.
Where it is taken in Turkey
IGCSE is offered by international schools and by a number of private schools running a British stream. Students whose school does not offer it, or does not offer a particular subject, sit it as private candidates through authorised centres.
The private candidate route is common and carries no disadvantage in the result. The certificate does not distinguish between the two.
Equivalence and the national system
A student following the IGCSE and A Level route towards a Turkish university will need diploma equivalence at the end, and that process is based on the leaving qualification, which is A Level rather than IGCSE.
This is covered under YOK equivalence. The point to carry here is that IGCSE grades are not the document the equivalence process examines.
The genuine value for a student in Turkey
The qualification is examined in English against an international specification, which means the student learns the subject vocabulary in English two years before it is needed.
Students who move from a national curriculum into an English medium sixth form without this step frequently find the first term harder than the content warrants, because the language and the content arrive together.
What to decide early
Whether the route ends in A Level, IB, or a return to the national system. Each of the three reads IGCSE differently, and the subject selection made at fourteen is difficult to reverse at sixteen.