Teratozoospermia Index (TZI)
Fertility marker
Teratozoospermia Index
Teratozoospermia Index (TZI)
The average number of defects per abnormal sperm. A single sperm can have a head defect, a mid-piece defect and a tail defect at once, and this captures how many faults the abnormal ones carry on average.
PED Notes
Reported alongside morphology by labs using strict WHO criteria, and usually flagged above about 1.80. It adds information morphology alone does not: two men can both have 4% normal forms, but one whose abnormal sperm carry a single minor defect each is in a different position from one whose abnormal sperm are multiply defective. A rising index alongside falling morphology suggests spermatogenesis is under more strain rather than simply producing fewer good cells, which is the pattern seen with suppression, heat and oxidative stress.
When high
A raised index means the abnormal sperm carry multiple defects each, rather than one minor fault. Interpret it with Sperm Morphology, not instead of it.
The drivers overlap almost entirely with fragmentation: heat, oxidative stress, varicocele, infection, smoking and suppressed spermatogenesis. See Sperm DNA Fragmentation for the practical list, since anything that lowers fragmentation tends to improve this too.
Timeline: a full spermatogenic cycle is about 74 days, so retest at 3 months.
History Chart
Reading History
Frequently Asked Questions
Reference Ranges
Standard Range
Not available