Semen Analysis

Macroscopic Evaluation

This is simply the visual inspection and measurement of the sample.  Firstly, the volume is measured and is typically between 1.5 – 5.0 ml.   To give some sense of scale, a teaspoon contains around 5ml of liquid.  Next is the appearance of the sample.  It should be white, maybe slightly off white and translucent, that is, you cannot see through it but it allows light to pass through.  An opaque sample can be a sign of infection.

Immediately after ejaculation the semen is a viscous, sticky semi-liquid which is quite difficult for the sperm to swim through.  This is an evolutionary adaptation to deposit the sperm in in one location, providing a concentrated base for the journey to the egg.  After about 10 minutes the semen undergoes a process that biochemically resembles blood clotting, except in reverse, and the semen becomes a free flowing liquid.  This process is called liquefaction and is usually reported in the analysis as being complete or incomplete.  Incomplete liquefaction is not necessarily a cause of infertility, but like an abnormal sample volume, it may give an indication to the functioning of accessary sex organs such as the seminal vesicles or prostate.

The pH of the sample is measured and should be slightly alkaline at pH 7.2 or greater.  An acidic sample with pH less than this is likely to indicate problems related to the seminal vesicles.


 Microscopic Evaluation

Initial examination of the sample under the microscope will reveal the presence of any cellular debris and also whether the sperm are freely swimming or agglutinated together in clumps.  Either of these situations can indicate infection or trauma.  A certain amount of cellular debris can be disregarded, but high levels of agglutination may impact of fertility.


Sperm Count

This is usually expressed as the number of sperm per millilitre (ml) of semen; as such is it really sperm concentration.  The total sperm count is the concentration multiplied by the volume (in ml).  The minimum sperm concentration that is considered within the normal range is 15 million/ml.  So a man at the minimum end of the normal range of concentration and volume (1.5ml) would have a total sperm count of 1.5 x 15million = 22.5 million sperm in total.  Having a concentration lower than 15 million/ml is termed oligozoospermia, a volume of less than 1.5ml is called hypospermia.  As you can see the total numbers of sperm are extremely large, especially when you consider that only a single spermatozoon is required to fertilise the egg.  Having a low sperm count does not mean that you are infertile, lower sperm counts may reduce the chances of a pregnancy each month.  While ever there are any sperm present there is always the possibility of pregnancy.  The chances of pregnancy can be increased dramatically by assisted reproduction in which the sperm are prepared and enriched in the laboratory.



This refers to two things, the number of sperm that are actively swimming (total motility), expressed as a percentage; and secondly the percentage of sperm that are making forward progress, usually termed progressive motility.  Some sperm will be swimming actively, but going in circles or spinning on their axis, which is not likely to get them to the egg.  These sperm would be termed motile but non-progressive.  It is really the sperm that are both motile and progressive (swimming in a straight line) that is the key number.  The medical term used to describe poor motility is asthenozoospermia.  The lower value of the normal fertile range for total motility is 40% and for progressive motility is 32%.  These figures seem a little arbitrary, and they are simply based on statistics, but motility remains the single most useful predictor of fertility.

Having said this, assisted reproduction techniques now extend to selecting a single sperm and physically injecting it into the egg.  This technique is called intracytoplasmic sperm injection (ICSI), so even men with zero motility can become fathers so long as some sperm can be found.



Morphology simply refers to the shape of the sperm.  Part of the sample is prepared to allow easy visualisation of sperm structure so that the proportion of normal sperm, and those falling into tightly defined morphological groups may be counted.  The World Health Organisation (WHO) lay down strict morphological criteria defining the various sperm defects and these are usually simplified for reporting as the percentage of sperm exhibiting head, midpiece or tail defects.  The effect of this is that quite often only a very small proportion of sperm are categorised as normal.  In fact a semen sample is considered morphologically normal if 4% of the sperm fulfil the normal criteria.  Put another way, a sample may exhibit 96% abnormal morphology and still be within the normal range.

The WHO morphology definitions are very specific so that semen quality can be recorded extremely accurately.  Having abnormally shaped sperm is known as teratozoospermia.   It’s quite likely that some of the sperm that are categorised as abnormal may actually function normally, but even if this were not so, an average semen sample containing say 100 million sperm in total, where 96% of them were classed as morphologically abnormal, would still have 4 million normal sperm available!



Vitality refers to the proportion of sperm that are dead or alive.  Of course all the sperm that are actively swimming are alive, but it is not possible to distinguish live from dead sperm among those that are immotile.  This is achieved by mixing some of the sample with a dye that is excluded by living cells, but is able to enter dead cells staining them blue.  The results are reported as the percentage of sperm that are alive.  The minimum vitality that is considered normal is 58% and the medical term for values lower than this necrozoopermia.   Tests of vitality are particularly important in situations where there is very low sperm motility and ICSI is being considered.


Other Cells

There may be some other cells in the ejaculate, most notably white blood cells (lymphocytes), red blood cells (erythrocytes) or immature sperm cells.  Erythrocytes are distinctively red in colour, small and without a nucleus; their presence is called haemospermia and indicates infection or trauma.   Similarly, white blood cells indicate infection or inflammation, but these cells are often difficult to distinguish from immature sperm cells.  Both these types of cells are referred to as round cells and they can be identified by detecting cells that express an enzyme called peroxidase.  Immature sperm cells are peroxidase negative and most immune cells are positive for peroxidase.  The maximum concentration of round is considered to be normal is around 1.0 million/ml.


Antisperm Antibodies

Antibodies are proteins produced by the immune system that bind to foreign invaders in the body such as viruses and bacteria.  They are one of the ways in which the body discriminates between self and non-self and we would not normally expect them to bind to our own cells.  However, the testis is normally protected and sperm do not come into contact with the immune system.  This can occur in cases of testicular injury, biopsy or vasectomy reversal and in a few cases a man may make antibodies against his own sperm.

The mixed antiglobulin reaction (MAR) test is included in some routine semen analyses and this is able to detect antisperm antibody.  Results are usually expressed as the percentage of sperm bound by antibody, and two subclasses of antibody (IgG and IgA) are commonly recorded.  Anything less than 10% is considered negative and due to non-specific binding, but there are no concrete reference values for a positive result.  The WHO currently regard 50% or greater as a level likely to affect fertility, but this value is pending until further evidence is available.  Problems involving antisperm antibody can usually be successfully overcome using IVF or ICSI.