Telomere length measurement by qPCR – Summary of critical factors and recommendations for assay design

•Telomere length has been investigated as a cellular aging biomarker for environmental exposure and life style factors.•Inconsistencies using the qPCR telomere length method highlight the need for a careful methodological analysis of the whole process.•We summarize each critical step in qPCR telomere length assay and provide guidance and recommendations based on current knowledge.•We suggest that the telomere research community collaborate on the development and implementation of standardized protocols.