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Perspectives and Editorials |
If illness of the testes resulted in altered spermatogenesis, the number of sperm produced per day might be affected. Daily sperm production is a rate—that is, 106 sperm/d. Hence, estimation of daily sperm production based on ejaculated semen requires a rate function measure. The appropriate rate function is TSperm/h of abstinence, and calculation of this measure requires accurate information on both TSperm and abstinence interval.
Most clinicians recognize that several samples of semen should be evaluated before reaching conclusions about a patient's testes function from a quantitative perspective. This practice is in recognition of substantial intrasubject variation in TSperm, in part resulting from differences in abstinence interval. Advice to a subfertile couple need not be based on information from a highly accurate or precise semen analysis (Jequier, 2005). However, imprecision and failure to measure a rate attribute could hamper an epidemiologic-andrologic team's capability to detect a moderate deficiency in sperm production in a given individual.
Perusal of the World Health Organization manual (1999) or epidemiologic literature will convince readers that emphasizing sperm concentration and ignoring TSperm is common practice. Common reporting does not make sperm concentration meaningful for evaluation of spermatogenesis. It is hoped that this perspective will convince readers to restore concentration of sperm per milliliter of semen to status as an unnecessary calculation in measuring TSperm and to abandon reporting sperm concentration. Indeed, the revised World Health Organization manual (2009) states that "concentration of spermatozoa in the semen... provides no information on the physiology of either the testes or the accessory organs."
Emission and Ejaculation
Emission involves contractions of smooth muscles of the distal caudae
epididymides and vasa deferentia to move sperm into the ampullae, followed by
further contractions to move boluses of sperm suspension from the ampullae
(and possibly more from the vasa deferentia and distal caudae epididymides)
into the pelvic urethra (Pabst,
1969). The initial bolus of sperm is diluted and mixed with fluid
from the prostate gland, and later boluses with fluid from the vesicular
glands (Lundquist, 1949;
Amelar and Hotchkiss, 1965;
Eliasson, 2003). Ejaculation is
a reflex reaction to the buildup of semen in the pelvic urethra, and involves
contractions of striated muscles surrounding the urethra, to propel the
mixture of sperm and fluid out the urethra, as several squirts followed by
additional expulsions of fluid from the vesicular glands.
Given this scenario, it is obvious that several boluses of concentrated
sperm suspension provide the entire population of sperm in an ejaculate (ie,
TSperm). When the sperm are within the ampullae and vasa deferentia, they
occupy a minute volume (Vsperm) and are in small volumes of fluid
(Vampullae and Vvasa). During emission, fluids from the
accessory sex glands (Vasg) are added to provide additional volume,
although the contributions from any gland can vary substantially.
Vasg typically is far greater than what accompanies the sperm as
Vampullae + Vvasa (
3.5 mL vs 0.25 and <0.20
mL; latter 2 values calculated from Pabst,
1969). Collectively, these fluid volumes total to Vseminal
plasma and ejaculate volume is the total of Vseminal plasma
plus Vsperm. Ejaculate volume and Vseminal plasma
usually are considered equivalent, and Vsperm usually is ignored
(as is volume of any extraneous cells).
Quantitative Analysis of Semen
From the previous section it should be obvious that ejaculate volume does
not reflect quantitative or qualitative normalcy of spermatogenesis or
function of any individual organ. It should be equally obvious that TSperm
provides the basis to estimate quantitative normalcy of spermatogenesis, if
procedures for collection of semen and measurement of TSperm were appropriate.
Number of sperm per milliliter of semen can never provide an estimate of sperm
production by the testes or production of fluid by any accessory sex gland or
group of glands, or adequately describe an ejaculate.
Volume should be measured gravimetrically in the original collection container, to eliminate loss of material (Eliasson, 1971; Cooper et al, 2007). Volumetric measurement after aspirating semen into a pipette or pouring semen into a graduated cylinder or tube results in underestimation of ejaculate volume, and the extent of error can not be predicted accurately.
For practical reasons, all sperm in an ejaculate are not enumerated. Rather, after semen liquefies it is thoroughly mixed and a very small measured aliquot is removed. This aliquot usually is diluted to facilitate counting, using appropriate procedures (eg, World Health Organization, 1999, 2009), to give a primary measurement—number of sperm counted in a minuscule volume of semen (eg, 10–6 or 10–5 mL). Replicate values for other minuscule volumes from the diluted aliquot, or several aliquots representing the total sample, are averaged.
The mean number of sperm counted in a known miniscule volume (eg, 87 sperm) then is multiplied up, using an appropriate factor (eg, 106) and ejaculate volume (eg, 2.7 mL) to give a value for TSperm (235 x 106 sperm in this example). There is no need to calculate number of sperm per milliliter of neat semen when TSperm and ejaculate volume are reported.
Use of Data
Persons working with semen would be well advised to recognize that the
biologically important quantitative attributes of an ejaculate are TSperm and
volume. MacLeod and Gold
(1952:707) suggested that
"total number of spermatozoa [ie, TSperm] delivered to the ejaculate is
an adequate measure of the activity of the germinal epithelium." They
were not quite correct, because TSperm is not "adequate"; a rate
function is needed. TSperm/h of abstinence is a rate function providing an
estimate of a man's daily sperm production. It is a derived seminal attribute.
A single value for TSperm/h is imprecise, so a mean value for 2, 3, or 
6
samples provided after an appropriate abstinence interval is preferable
(Amann, 2009;
Amann and Chapman, 2009).
Unusually high or low seminal volume could point to aberrant function of
accessory sex glands (Eliasson,
2003).
With respect to potential for impregnating a female, for the majority of ejaculates information on sperm concentration, TSperm, or even total number of fully functional sperm is of no predictive value because values will be above a "threshold." Only at the very low end of the full range of values for such seminal attributes is there a relationship where "more is better." Over most of the range there is no relationship (eg, Slama et al, 2002). This has been demonstrated repeatedly in robust studies with model animals.
Conclusion
When evaluating testes and accessory sex gland function by typical seminal
analysis, an ejaculate is best quantified by volume and TSperm. By itself,
number of sperm per milliliter of neat semen can not accurately reflect testes
function. However, provided abstinence interval is appropriate, TSperm for an
entire ejaculate can provide a value reflective of sperm production by the
testes when expressed as TSperm/h of abstinence.
References
Amann RP. Considerations in evaluating human spermatogenesis on the
basis of total sperm per ejaculate. J Androl. 2009; 30: 626
–641.
Amann RP. Tests to measure the quality of sperm at spermiation. Asian J Androl. In press.
Amann RP, Chapman PL. Total sperm per ejaculate of men: obtaining a
meaningful value or a mean value with appropriate precision. J
Androl. 2009;30: 642
–649.
Amelar RD, Hotchkiss RS. The split ejaculate. Its use in the management of male infertility. Fertil Steril. 1965; 16: 46 –60.[Medline]
Cooper TG, Brazil C, Swan SH, Overstreet JW. Ejaculate volume is
seriously underestimated when semen is pipetted or decanted into cylinders
from the collection vessel. J Androl. 2007; 28: 1
–4.
Eliasson R. Standards for investigation of human semen. Andrologia. 1971; 3: 49 –64.
Eliasson R. Basic semen analysis. In: Matson P, ed. Current Topics in Andrology. Perth, Australia: Ladybrook Publishing; 2003: 35 –89.
Jequier AM. Is quality assurance in semen analysis still necessary?
A clinician's viewpoint. Hum Reprod. 2005; 20: 2039
–2042.
Lundquist F. Aspects of the biochemistry of human semen. Acta Physiol Scand. 1949; 19(suppl 66): 1 –105.[CrossRef]
MacLeod J, Gold RZ. The kinetics of human spermatogenesis as revealed by changes in the ejaculate. Ann N Y Acad Sci. 1952;55: 707 –724.[CrossRef][Medline]
Pabst R. Untersuchungen über Bau und Funktion des menschlichen Samenleiters. Z Anat Entwickl-Gesch. 1969; 129: 154 –176.[CrossRef][Medline]
Slama R, Eustache F, Ducot B, Jensen TK, Jørgensen N, Horte
A, Irvine S, Suominen J, Andersen AG, Auger J, Vierula M, Toppari J, Andersen
AN, Keiding N, Skakkebæk NE, Spira A, Jouannet P. Time to pregnancy and
semen parameters: a cross-sectional study among fertile couples from four
European cities. Hum Reprod. 2002; 17: 503
–515.
World Health Organization. WHO Laboratory Manual for the Examination of Human Semen and Sperm–Cervical Mucus Interaction. 4th ed. Cambridge, United Kingdom: Cambridge University Press; 1999.
World Health Organization. WHO Laboratory Manual for the Examination and Processing of Human Semen. 5th ed. Geneva, Switzerland: World Health Organization; 2009.
This article has been cited by other articles:
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  R.P. Amann Evaluating testis function non-invasively: how epidemiologist-andrologist teams might better approach this task Hum. Reprod., January 1, 2010; 25(1): 22 - 28. [Abstract] [Full Text] [PDF]
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 R. P. Amann Considerations in Evaluating Human Spermatogenesis on the Basis of Total Sperm per Ejaculate J Androl, November 1, 2009; 30(6): 626 - 641. [Abstract] [Full Text] [PDF]
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