The SDI®-test

SDI is an abbreviation for Sperm DNA Integrity.

The SDI®-test examines if the sperm DNA integrity. The result of the test is the DFI-value which shows if the DNA is robust (low DFI) or fragile (increased or high DFI).

Fragile DNA will easily become damaged when the sperm produces energy to swim or fertilize an egg. This process is also called sperm DNA fragmentation.

Understanding DFI

Strictly spoken, DFI is a precise measure for the percentage of sperm where the test is able to identify actual fragmentation (damage) to the DNA. Ideally, the DFI should be as low as possible. A DFI of 25 implies that it is almost impossible for a couple to achieve a spontaneous pregnancy.

A general misunderstanding is that a semen sample with a DFI of 25% still contains 75% normal cells. This is not correct.

To understand DFI, you need to think of an iceberg.
The part of the iceberg that we can see is equal to DFI. Most of the iceberg is below the surface of the water. This part of the iceberg is equal to the proportion of sperm with fragile DFI. So in a sample with a DFI of 25%, almost all other sperm contains fragile DNA. After a natural intercourse, the sperm will have to swim the long way through cervix, uterus to find an fertilize the egg in the oviduct. When the sperm has reached that far, all sperm will have DNA fragmentation and pregnancy will not be achieved.

DFI and fertility

DFI varies from 0 to 100%. A low DFI indicate that the DNA is robust. The higher the DFI is, the more fragile the DNA is.

DFIDNA-fragilityFertilityProportion of infertile couples
Below 15Low (=robust DNA)Normal50%
15 to 25ModerateReduced25%
Above 25HighStrongly reduced25%