Semen analysis evaluates a man's sperm and semen to determine the cause of infertility or to confirm the success of a vasectomy. Semen is the thick yellow-white male ejaculate containing sperm; sperm are the male sex cells that fertilize the female egg (ovum) and contain the genetic information that the male will pass on to a child.
Abnormalities of sperm and semen can cause male infertility, and semen analysis is an initial step in investigating why a couple has been unable to conceive a child. Vasectomy is an operation done to sterilize a man by stopping therelease of sperm into semen. Success of vasectomy is confirmed by the absence of sperm in semen.
The semen analysis test is usually done manually, though computerized test systems are available. Many laboratories base their procedures on standards published by the World Health Organization (WHO).
The volume of semen in the entire ejaculate is measured. The appearance, color, thickness, and pH is noted. A pH test looks at the range from a very acidsolution to a very alkaline solution. Semen, like many other body fluids, hasa standard pH range that would be considered optimal for fertilization of the egg to take place. The thick semen is then allowed to liquify; this usuallytakes 20-60 minutes.
Drops of semen are placed on a microscope slide and examined under the microscope. Motility, or movement, of 100 sperm are observed and graded in categories, such as rapid progressive or immotile.
The structure of sperm (sperm morphology) is assessed by carefully examiningsperm for abnormalities in the size and shape in the head, tail, and neck regions. WHO standards define normal as a specimen with less than 30% abnormal forms. An alternative classification system (Kruger's) measures the dimensionsof sperm parts. Normal specimens are allowed 14% or less abnormalities.
Sperm are counted by placing semen in a special counting chamber. The sperm within the chamber are counted under a microscope. White blood cells are recorded; these may indicate a reproductive tract infection. Laboratories may testfor other biochemicals such as fructose, zinc, and citric acid. These are believed to contribute to sperm health and fertility.
Results of semen analysis for infertility must be confirmed by a second analysis seven days to three months after the first. Sperm counts may vary from day to day.
Semen analysis to confirm success of vasectomy is concerned only with discovering if sperm are still present. Semen is collected six weeks after surgery.If sperm are seen, another specimen is collected two to four weeks later. Thetest is repeated until two consecutive specimens are free of sperm.
A man should collect an entire ejaculate, by masturbation, into a container provided by his physician. To examine the best quality sperm, the specimen must be collected after two to three days of sexual abstinence, but not more than five to seven days. The specimen must not come into contact with any spermicidal agents used by a female partner for birth control purposes. The man should not have alcohol before the test.
A semen specimen to investigate infertility must be brought to the testing laboratory within one hour of obtaining it. Timing is not as critical for the postvasectomy test but the semen must be kept at body temperature. The most satisfactory sample is one obtained in the lab rather than at home.
WHO standards have established these normal values:
- Volume less than or equal to 2.0 mL
- Sperm count greater than or equal to 20 million permL
- Motility (movement of the sperm) value is greater than or equal to 50% with forward progression, or greater than or equal to 25% with rapid progression within 60 minutes of ejaculation
- Morphology greater than orequal to 30% with normal forms
- White blood cell count less than 1 million per mL.
If infertility continues, despite normal semen analysis and female studies, further tests are done to evaluate sperm function.
Abnormalities of semen volume and liquidity, and sperm number and morphologydecrease fertility. These abnormalities may be inherited or caused by a hormone imbalance, medications, or a recent infection. Further tests may be done to determine the cause of abnormalities.