Sperm vitality on a semen analysis: reference range and what a low result means
Vitality answers a question that motility cannot: are the sperm that are not moving dead, or alive but unable to swim? It is not part of every basic semen analysis, but the WHO recommends it whenever fewer than about 40% of sperm are progressively motile. This page explains how vitality is tested, the WHO 2021 reference limit of 54%, and why the gap between vitality and motility matters.
What your number means
| Very low | under 30% live | Necrozoospermia. A high proportion of dead sperm points to a problem in the epididymis or genital tract: infection, prolonged abstinence, antisperm antibodies, or a toxic exposure. Needs investigation, and often ICSI with live-sperm selection if not correctable. |
|---|---|---|
| Low | 30% to 53.9% live | Below the WHO reference limit. Compare with total motility: if vitality is much higher than motility, many sperm are alive but immotile (a tail problem); if vitality roughly equals motility, the immotile sperm are mostly dead. |
| Normal | 54% to 90% live | Within the fertile range. Vitality should always be at least as high as total motility; a motile sperm is by definition alive. |
| High | over 90% live | Excellent. Typical of a fresh sample with short transit time. If total motility is low despite very high vitality, the sperm are alive but not swimming, which points to a structural tail defect rather than cell death. |
What it measures
Vitality tests check whether the sperm cell membrane is intact, which is the working definition of a live sperm. The most common method is the eosin-nigrosin stain: dead sperm with damaged membranes take up the red eosin dye, while live sperm exclude it and stay white against the dark nigrosin background. The lab counts at least 200 sperm and reports the percentage unstained.
The alternative is the hypo-osmotic swelling (HOS) test, in which sperm are placed in a dilute solution; live sperm with intact membranes swell and their tails curl, while dead sperm do not react. The HOS test does not kill the sperm, so it can be used to pick live immotile sperm for ICSI, which eosin cannot.
Vitality is assessed on the same timeline as motility, within an hour of ejaculation, because sperm begin to die once outside the body. A sample that was delayed or chilled will show low vitality and low motility together, which is an artefact rather than a finding.
Why it matters for fertility
On its own, vitality is a secondary parameter. Its value lies in interpreting motility: a sample with 20% total motility and 25% vitality is mostly dead sperm, whereas a sample with 20% motility and 75% vitality has plenty of live sperm that cannot swim. Those two situations have different causes and different solutions.
The 54% limit is the 5th percentile of the WHO 2021 fertile reference group. Vitality below that limit alongside low motility suggests a process that is killing sperm after they are formed, usually in the epididymis or during storage in the genital tract. Vitality well above motility suggests the sperm are healthy but their tails are not working.
For assisted reproduction the distinction is decisive. Live but immotile sperm can be identified with a HOS test or laser-assisted selection and used for ICSI with good fertilisation rates. Dead sperm cannot fertilise anything, so a truly necrozoospermic sample may need surgically retrieved testicular sperm, which are usually alive even when ejaculated sperm are not.
What lowers it
The most common cause of low vitality is prolonged abstinence. Sperm stored in the epididymis for more than about a week begin to die, so a sample after 10–14 days of abstinence can show high count but low vitality and motility. Frequent ejaculation for a few days before the test, followed by 2–3 days of abstinence, often corrects this on its own.
Genital tract infection, particularly epididymitis or prostatitis, and leukocytospermia kill sperm through reactive oxygen species and bacterial toxins. Antisperm antibodies, seen after vasectomy reversal, injury or infection, bind to the membrane and are associated with lower vitality. Spinal cord injury and hyperthermia have both been linked to necrozoospermia.
Toxic exposures reduce vitality: heavy smoking, some solvents and pesticides, and certain medications including chemotherapy. Varicocele contributes through heat and oxidative stress. Collection problems — lubricant, saliva, soap residue, a cold or delayed sample — produce an artificially low result that resolves on a properly collected repeat.
How to improve it
Correct abstinence first. If the low result came after a long gap, ejaculate daily for 3–4 days, then abstain 2–3 days and retest. For men with confirmed necrozoospermia, some clinics recommend very short abstinence (24 hours or less) or even a second ejaculate an hour after the first, because fresher sperm from the testis have higher vitality.
Treat any infection identified on semen culture, and address leukocytospermia. Stop smoking, remove heat exposure and consider varicocele repair where indicated. Antioxidant supplements may modestly improve vitality by reducing oxidative stress, though the trial evidence is thin.
If vitality is persistently low despite these steps, the practical route is ICSI using live sperm selected with a HOS test or, where ejaculated sperm are mostly dead, testicular sperm extraction. Testicular sperm are commonly used in necrozoospermia because they have not been exposed to whatever is killing sperm in the epididymis.
When to retest
Repeat a low vitality result after correcting abstinence (2–3 days) and collecting on site, usually within 2–4 weeks rather than waiting a full 3 months, because abstinence and collection effects are the commonest explanation and they show up immediately.
If the repeat is still low, retest 3 months after treating any infection or other cause. Ask the lab to report vitality and motility together so the gap between them can be tracked.
Persistently low vitality (under 30%) on two properly collected samples warrants a semen culture, an antisperm antibody test and a reproductive urology referral to plan sperm retrieval or selection for ICSI.
Tests that measure this
Related diagnoses
Common questions
Is vitality the same as motility?
No. Motility is the percentage of sperm that move; vitality is the percentage that are alive. Every motile sperm is alive, but an immotile sperm may be alive or dead. Vitality is always equal to or higher than total motility. The difference between them is the share of sperm that are alive but cannot swim.
Why was vitality not on my semen analysis report?
Many labs only perform a vitality stain when total motility is low, typically under about 40%, because when most sperm are moving the vitality result adds little. If your motility is low and vitality is missing, ask the lab to add it on the next sample; it changes the interpretation of the low motility.
What is necrozoospermia?
Necrozoospermia is a high percentage of dead sperm in the ejaculate, usually defined as vitality under about 30–40% or under the WHO limit of 54% with correspondingly low motility. It is uncommon and most often caused by prolonged abstinence, infection, antisperm antibodies or a toxic exposure. It is frequently reversible, and where it is not, live sperm can usually be retrieved from the testicle for ICSI.
Can live but immotile sperm be used for IVF?
Yes, with ICSI. The embryologist uses a hypo-osmotic swelling test or a laser to identify sperm that are alive despite not moving, then injects one into each egg. Fertilisation rates are lower than with motile sperm but often acceptable. This is why the vitality test matters: it tells the clinic whether that option exists.