The semen parameters from same individuals are highly variable. Many conditions including the duration of ejaculatory abstinence, activity of the accessory sex glands, analytical errors, and inherent biological variability account for such discrepancies [15–18]. In one study, the within-subject variability of 20 healthy subjects assessed over a 10-week follow-up ranged from 10.3 to 26.8 % [15]. Sperm concentration showed the highest within-subject variation (26.8 %), followed by morphology (19.6 %) and progressive motility (15.2 %) whereas vitality had the lowest variation (10.3 %). The utility of population-based reference values is related to the individual variability of a particular analyte. Reference values of analytes with attributable individuality, including the ones routinely assessed in the semen , are generally of limited utility. It means that individual subjects could present results that were very unusual for them, and such results might have been accounted when establishing the reference thresholds. For the aforesaid reasons and other uncontrolled factors such as the regression toward the mean, it is impossible to take the results of a single-semen specimen as a surrogate for a man’s ability to father a child unless when at extreme low levels [19]. Regression toward the mean is the phenomenon in which a variable would tend to be closer to the average on a second measurement if it was extreme in its first measurement. This uncontrolled factor should be contemplated when designing studies involving semen analysis because following an extreme random event the next random event is less likely to be extreme. It has been shown that sperm concentration and motility were significantly higher in the second test in men with previous abnormal semen analyses results [20]. Regression toward the mean can be reduced in its magnitude by using means of multiple samples (two or three in the case of semen analysis). Hence, it is prudent that clinicians request at least two semen specimens following 2–5 days of ejaculatory abstinence to allow a better understanding of the baseline semen quality status of a given individual [21–23].

Up to 30 % of men with difficulties to father a child have no demonstrable abnormalities after an initial male infertility workup. Additional tests have been developed to unravel functional disorders and other sperm abnormalities that cannot be identified by conventional semen analysis [11, 24]. Some of these tests include the hypo-osmotic swelling test, computer-assisted sperm analysis, antisperm antibody test, sperm penetration assay, hemizona assay, reactive oxygen species (ROS) tests, and sperm chromatin integrity test [25]. Despite being available, there are inherent difficulties to set up these tests including cost of equipment and technical complexity. In addition, their predictive value in assessing the male fertility status is either variable or unknown [26]. Not surprisingly, many couples with unexplained infertility choose assisted reproduction techniques (ART) because of their widespread availability and overall success irrespective of the male infertility cause [27]. Yet, the assessment of sperm oxidative stress (OS) and DNA integrity has gained clinical importance in recent years. OS, which is present anywhere from 30 to 80 % in infertile men, is a result of the generation of ROS from contaminating leukocytes, defective sperm, and antioxidant depletion [28, 29]. ROS target sperm DNA molecules and ultimately affect the quality of the genetic material transmitted from the parents to the offspring. Damage to sperm DNA integrity can also result from apoptosis during spermiogenesis , alterations in chromatin remodeling during spermiogenesis, as well as exposure to environmental toxicants and gonadotoxins such as chemotherapy and radiotherapy [30]. Abnormal levels of DNA damage are observed in approximately 5 and 25 % of infertile men with normal and abnormal semen analysis, respectively [31–33]. Therefore, some authors propose that the assessment of both conditions might be included to the male infertility workup algorithm [34, 35].

Accuracy, the degree to which the measurement reflects the true value, and precision, the reproducibility of the results, are vitally important for clinicians who rely upon the values provided by the laboratory to direct the further work-up, diagnosis and counseling of the infertile male [36]. When both accuracy and precision are assured, the clinician is able to rely upon the semen analysis results to provide adequate counseling to the infertile couple. However, data from surveys of laboratory practice in the USA and the UK indicate that semen analysis techniques are still poorly standardized.

Among 536 clinical laboratories in the USA only about 60 % reported abstinence and indicated the criteria adopted for sperm morphology assessments. Moreover, fewer than half of them performed quality control for commonly assessed parameters such as sperm counts, motility, and morphology [37]. A survey involving 37 laboratories in the UK about the methods used to assess sperm morphology revealed that only 5 % complied with all WHO guidelines [38]. In the aforementioned study, participating laboratories had high interobserver variability when evaluating the same specimen. This data were corroborated by another study in which interlaboratory coefficient of variation was as high as 34 % for sperm concentration, 20 % for total sperm motility, 40 % for sperm vitality, and 70 % for sperm morphology (strict criterion) [39]. Discrepancies were also seen in laboratories enrolled in quality control programs, thus indicating that there is a need of global standardization among the laboratories and the providers of external quality control [40].

Owed to its complex nature, semen analysis should ideally be carried out in a dedicated andrology laboratory attired with experienced technicians, internal and external quality control, validation of test systems, quality assurance during all testing processes, and proper in place communication with clinicians and patients [41]. Despite being nonspecific for identifying male factor infertility etiologies, semen analysis is often the gateway test from which multiple expensive and often invasive treatments are based. Therefore, the importance of a reliable andrology laboratory cannot be underestimated .