TDL Andrology is updating its reference values to those now given in the most recent WHO guidelines (2021).

Reference values for semen parameters in these guidelines have been determined from data providing the semen characteristics of a reference population of men whose partners had time to pregnancy of 12 months or less. These men were from 8 countries and 5 continents from where data had not previously been reported.

The reference values that TDL will report will be as the lower 5th centile. Clinical decision limits will be displayed in brackets. The lower 5th centile represents the level below which only 5% of the men in the reference population were found. This demonstrates that the reference values do not represent distinct limits between fertile and subfertile men, but rather it suggests that men are more likely to be fertile if they are above the reference value and vice versa.

The decision limit is based on clinical and statistical considerations that point to a need for a certain diagnostic, or therapeutic, intervention as they are associated with a higher risk of infertility.

If you would like to discuss the information related to these reference values in more detail, please contact:

Andrew Dawkins
Head of TDL Andrology 

020 7025 7940

Prof Sheryl Homa
Consultant Clinical Lead, TDL Andrology 

020 7025 7940