Editorial Commentary on Draft of World Health Organization Sixth Edition Laboratory Manual for the Examination and Processing of Human Semen

Semen examination is the cornerstone of the evaluation of male fertility potential. Despite its apparent simplicity, it is a complex series of assessments with highly variable results that are subject to interpretation. The semen analysis is used to gauge reproductive potential and guide the clinician in management of the infertile couple. Over the past 40 years, the World Health Organization (WHO) Infertility Task Force has attempted to standardize the methodology of semen examination so as to bring uniformity and relevance to the test. The 1st edition of the “Laboratory Manual for the Examination and Processing of Human Semen” was published in 1980. Since then, four more editions of the WHO manual have been published, each attempting to reflect global male population demographics, to address limitations from previous versions, and to incorporate technological and scientific evolution in the field of reproduction. Currently, the 5th edition of the WHO manual, published in 2010, is implemented worldwide, and is considered one of the most used, yet contested documents in the field of male infertility [1]. In March 2021, the WHO released a preliminary draft of the 6th edition of its manual for public review and suggestions (https://www.who.int/publications/i/item/9789241547789). Essentially, the new manual comprises three parts: semen examination; sperm preparation and cryopreservation; and quality control and assurance. The procedures for semen examination include basic (routine) examinations, extended examinations (which may be used by laboratories or clinicians in certain situations), and advanced tests (which are not currently recommended for routine use and are primarily for research purposes). The 6th edition has presented the basic examination in a step-by-step and temporal manner, so that it can be reproduced precisely in any laboratory with the required equipment and expertise. The sections on extended and advanced examinations have been completely revamped in concordance with current clinical practice, with many older tests being abandoned and new tests being adopted. The purpose of this mini review and commentary is to familiarize fertility specialists with the principal changes proposed in the anticipated 6th edition of the WHO manual for human semen analysis. The advantages, limitations and clinical implications of these changes are discussed. 1. Use of decision limits to identify abnormal ejaculates The most important change proposed in the 6th edition is the adoption of decision limits to differentiate normal from abnormal ejaculates. The editors of the 6th edition acknowledge that the reference ranges described in the 5th edition should be abandoned as they are of limited value in differentiating fertile from infertile men. The 5th edition WHO manual utilized a population of 1,800 fertile men to obtain the reference distributions for semen parameters [1]. The lower 5th percentile was used to define the reference values for normal semen parameters. While the 5th percentile is commonly utilized as a statistical approach to determine cut-off norms in medical tests, this resulted in much controversy when applied to male fertility [2]. It has been argued that the 5th percentile is not applicable to assign normality in this case and proves unable to discriminate between fertile and infertile patients [3]. Several studies reported a shift of fertility status from abnormal to normal in 15% to 44% of patients by just using the 5th edition norms instead of the 4th edition [4,5,6,7]. It was therefore proposed that WHO reference ranges did not adequately reflect fertility dynamics of the male partner, with several investigators and clinicians believing that normal values were above the lower 5th percentile. With these limitations in mind, the editors of the 6th edition suggested using different reference limits because the previous reference ranges fail to differentiate fertile from infertile men [8]. Decision limits were introduced by Guzick et al [9], who proposed a two-level reference range narrative by defining an intermediate group of values. According to their data the sub-fertile population demonstrated a sperm concentration below 13.5×106/mL, sperm motility less than 32% and typical forms below 9%. Yet, the normal fertile subgroup had a sperm concentration greater than 48×106/mL, sperm motility over 63%, and normal morphology above 12%. Values between these two levels were categorized as intermediate fertility [9]. The 5th edition has been criticized for neglecting the female factor as an important confounder [3] and for both over- and under-representation of various regions of the world [4]. The editors of the 6th edition have acknowledged these limitations (Appendix 8.1 of the manual) and stipulated that semen examination cannot strictly differentiate between pathological and normal samples. Moreover, they recognize that using the lower 5th percentile is not the correct approach to identify normal or abnormal semen samples, and that semen analysis alone cannot predict fertility as this depends on multiple variables, particularly, female factors. Hence, the “normal” reference values of the 5th edition have been replaced by “decision limits” in the 6th edition. These are classified as “normal”, “borderline”, and “pathological”. A “normal” concentration is ≥20×106/mL, “borderline” lies between 10 to 20×106/mL, and “pathological” is