SEMEN ANALYSIS
Evidence-based medicine
Basic semen parameters and uncertainty of measurement
It is easy to forget that semen parameters are not measurable in SI units, nor is there any 'official' standard or calibrant to compare laboratory output to. Being subject to biological and procedural anomalies, it is no surprise that some consider the analysis to be more qualitative as opposed to quantitative. This means that the assessments we make can only ever be considered as estimates (not measurements) . The diagram above is a figure from the UK NEQAS scheme for sperm counts, which examines the agreement between laboratories for any given sample posted out to them. The typically wide distribution of results (from more than 250 labs) illustrates the effect that both procedural error and a lack of homogeneity can have on the result.
Indeed data from our own laboratory suggests that even with strict controls in place and individual man's diagnosis can vary from sample to sample, especially when the more subjective measures such as motility and morphology dominate. Strategies need to be implemented to account for both procedural and clinical anomaly in order to maximise the quality of information gained from each sample.
Clinical Value of Semen Analysis
Regardless of inaccuracies at the lab bench, procedural anomalies related especially to failure to follow specimen collection guidelines are common-place. Clinical anomalies such as partial retrograde ejaculation (RE), hyper-viscosity or agglutination can all contribute to the overall diagnostic uncertainty. Even in the best laboratories, the reliability of the diagnosis of male infertility is no more than 80%. In other words, if a man has a 'normal' semen analysis, his next test has an 80% chance of also being normal (data in preparation). This is why a confirmatory test is a must to ensure that a man is not mis-represented or mis-diagnosed.
Many other tests are or have been proposed as being useful additional indicators of sperm quality but patients and clinics are right to be wary of these until such time as the evidence-base in support of their use is unequivocal. Andrology consulting is happy to advise on how these tests work as well as discuss the evidence-base which supports their implementation. In each case, every test and sample is subject to the same level of uncertainty cause by procedural and clinical variability
Sperm Morphology
Sperm morphology assessment is perhaps subject to the highest level of uncertainty and the reason why some authors have described the parameter as lacking clinical value. Laboratories should concentrate on being able to identify those defect which we are certain will have a negative impact on sperm function. Laboratories which profess to measure individual sperm dimension and classifying them as abnormal because they fail to conform to an idealized shape/size run the risk of introducing method bias and a high level of uncertainty into the assessment since 'normal' is subjective, can be influenced by slide preparation and of course is always described from a heterogeneous and immotile population of sperm. There is currently no reliable assay that ensures that normal forms can be selected from either a motile or even viable population, therefore the relationship with clinical outcome (pregnancy) is always going to be weakened