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Semen analysis
Semen analysis is usually performed on a sample
collected after at least 36 to 72 hours of sexual abstinence. The
specimen is most often obtained after masturbation, but some
centres have approved a special condom for collection of the semen
during normal intercourse. After the sample has been obtained, it
must be taken to the clinic as soon as possible.
The analysis is carried out under direct visual and microscopic
examination.
First, the sample is assessed for the physical characteristics of
the semen, sperm density, motility and morphology (cellular
characteristics).
In addition, it is usual to check the pH of the semen (which should
be neutral or slightly acid: alkaline pH may indicate the presence
of infection), to check liquefaction and viscosity and to carry out
a test for the presence of antisperm antibodies.
Seminal levels of the sugar, fructose, are also measured as an
absence of fructose in the ejaculate implies obstruction distal to
the seminal vesicles. This is one of the few cases in which a
testicular biopsy may be indicated.
A concentration of white blood cells (leukocytes) in the semen has
an adverse effect on fertilisation and, especially with an alkaline
pH, may indicate a genital tract infection.
The table below lists the World Health Organisation (WHO) criteria
for normal semen analysis.
| WHO criteria for normal
semen analysis | | Criteria | Parameters | | Volume | 2.0-5.0 ml | | pH | 7.2 to 7.8 | | Sperm
concentration | 20 x 106 per ml or more | | Total sperm
count | 40 x 106 spermatozoa or
more | | Motility | 50% or more with forward
progression or 25% or more with rapid linear progression within 60
min after collection | | Morphology | 50% or more with normal
morphology | | Viability | 75% or more live (i.e. excluding
dye) | | White blood
cells | Fewer than 1 x 106 per
ml | | Zinc
(total) | 2.4 mol or more per
ejaculate | | Citric acid
(total) | 52 mol (10 mg) or more per
ejaculate | | Fructose
(total) | 13 mol or more per
ejaculate |
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Although sperm count (the number or density of
sperm in a sample) is critical, other factors such as sperm
motility and forward progression also appear to be important in
determining the fertilising capability of sperm.
Despite a low sperm count, many men with high-quality sperm (viable
and highly motile) may still be fertile. In addition, values that
were previously considered to be in the infertile range (e.g. a
sperm count less than 5 million/ml or sperm motilities of less than
20%) may actually be compatible with normal fertility.
Two or three semen samples should be analysed, since substantial
variability in sperm count and motility can be seen in successive
samples from the same individual. Sperm samples may be
characterised as potentially fertile, subfertile or infertile
(azoospermia).
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