Making sperm testing easy takes some serious science

Collect at home, post your sample, get clear results from our Oxford lab.


Underneath that simplicity is years of R&D and rigorous science making it all possible.

Jack measures five key sperm parameters: volume, concentration, total count, Estimated Original Total Motility, and Estimated Morphology Status. Some are measured directly. Others need a method built for the post.

SpermShield

Sperm samples change in the time between collection and analysis, especially when they travel through the post.


We’re often asked whether sperm “dies” before reaching us. That is exactly what SpermShield™ was built to address.


SpermShield™ is Jack’s proprietary preservation fluid for postal semen samples that extends the "life" of sperm cells. It is stable at room temperature for months before use, and keeps samples viable for testing for up to four days after activation, with no refrigeration or cold chain.


We did not repurpose an off-the-shelf preservative. We built one that is fit for purpose. That is why Jack is the UK’s first and only home sperm test you can return via any Royal Mail postbox.

Estimating motility

Even with SpermShield™, some decline in motility is expected during transit. Jack doesn’t simply report what arrives at our lab days later.


You tell us when you produced your sample. We log when it is analysed. Using the motility we measure, SpermShield™ validation data, and our correction model, we estimate motility at the time when your sample was produced. This is your Estimated Original Total Motility score.

Postal testing needs its own methods

A sperm test. Not a semen analysis.

A clinical semen analysis is performed on a fresh sample, within an hour of ejaculation. We do not pretend a delayed postal sample is the same as testing a fresh sample. We preserve what we can, adjust for what changes, and explain the limits clearly. That requires a different method and it is why we call Jack a Sperm Test, not a semen analysis.

Measured consistently, every time.

We use computer-assisted sperm analysis for count, concentration and Estimated Original Total Motility. The same software, measuring the same way, on every sample. Changes in your results should reflect your biology, not who analysed your sample that day.

We don’t outsource testing

Every sample is analysed at Jack’s own lab at the Wood Centre for Innovation in Oxford.


That matters because postal sperm testing is a full system. The kit, SpermShield™, sample handling, equipment, analysis protocols and results logic all need to work together.


By keeping the workflow in-house, we quality control the process end-to-end. That helps make the results more consistent, reliable and easier to interpret.

How accurate are results?

We benchmark our accuracy against the standards used in clinical semen analysis.

95%+

Reproducibility on direct measurements

Volume, concentration and count are measured directly from your sample. Postal transit does not meaningfully affect these.

Fresh analysis

Motility benchmarked against fresh analysis

Our motility estimates were calibrated against fresh semen analysis motility readings. The gap between our estimates and fresh readings was typically no different from the variation expected between two independent clinical readings of the same sample.

99%

Morphology threshold agreement

In validation, our estimation technique correctly classified samples as above or below the WHO 4% normal forms threshold in 99% of cases.

Results you can understand

Some numbers are direct. Some are estimated. Some are better expressed as a status than a score.

The point is clarity about where you stand, not noise around it.

Jack Fertility result bands from low to high

Bands give context

Most results sit in one of five bands, aligned to WHO 6th Edition reference data.

For most parameters, you still see the lab number. The band explains what it means at a glance.

Morphology is different

We do not report a morphology score, only whether your sample sits above or below the WHO 4% normal forms threshold.

A finer number can look precise. For morphology, it often is not.

Why LOW isn’t a number

LOW is aligned to the WHO 5th percentile and below, where clinical follow-up may be appropriate.

In that range, a precise-looking number can imply more certainty than a non-diagnostic test can responsibly provide, so we show a clear LOW status instead.

Borderline cases

Near the cutoff, normal variability matters.

If a result sits too close to classify confidently as LOW, we show BORDERLINE LOW instead.

The experts behind Jack’s science

Built and stress-tested by specialists across reproductive chemistry, fertility science, postal diagnostics and laboratory analysis.

Dr Daniel Fonseca

Dr Daniel Fonseca

Lead Scientific Advisor

“The interesting part of SpermShield was not simply preserving a sample. It was developing a formulation and workflow that could keep the sample analytically useful after a real postal journey. That meant stress-testing the chemistry against the conditions the sample would actually experience, not just what happens in an ideal lab setting.”
“SpermShield was never just about keeping a sample alive in theory. The real challenge was developing a formulation and workflow that could keep it analytically useful after an actual postal journey.”
Dr Danae Maragouthakis

Dr Danae Maragouthakis

NHS Doctor and sexual health advocate

“Having built and led a postal STI testing business, I know postal diagnostics only work when the full journey is designed properly: collection, transport, sample stability, analysis and communication of results. What stood out to me about Jack is that the methodology has been built around that reality from the start.”
“Having built and led a postal STI testing business, I know postal diagnostics only work when the full journey is designed properly: collection, transport, stability, analysis and communication of results.”
Dr Maryam Rahbar

Dr Maryam Rahbar

Embryologist and fertility researcher

Dr Raman Saggu

Dr Raman Saggu

AI-enabled healthcare analytics, biomarker diagnostics & neurotechnology

Ms Věra Kmoníčková

Ms Věra Kmoníčková

Andrologist and laboratory scientist

Professor Janet Shipley

Professor Janet Shipley

Research biologist and geneticist

Ready to know where you stand?

Get tested

Still have questions? Read the FAQ, contact us, or Ask Jack