Some labs have computer-aided semen analysis (CASA) machines that take a video of sperm cell swimming under the microscope and use analysis software to automatically count and characterize sperm. Various other technologies have been invented to measure sperm count, but no test is perfect. Depending on the method, the technology used, and the skill of the technician there are many sources of error that can occur. The most major sources of error include:

Counting error: Counting errors happen when sperm are moving too much, there are too many cells to easily count, or the technician doesn’t count enough squares to accurately estimate the true sperm count. One way to reduce this error is to de-activate, or “fix”, sperm so they can’t swim, making them easier to count. Increasing the number of grid squares or number of cells counted can also improve accuracy.

Sampling error: Going back to the swimming pool metaphor, imagine all the fish go to the bottom and you take a bucketful from the top. This would not be a good estimation of the true count. Similarly, sperm tend to hang out in clumps due to the viscosity and structure of semen. It is possible for a technician to draw a sample that has an abnormally high or low concentration of sperm. To overcome this challenge, some labs will require extensive sample mixing, or “homogenization”, to even out the distribution. They may also require technicians to draw and count multiple samples from the semen specimen to ensure that the counts are equivalent from sample to sample.

Performing a rigorous semen analysis can be both labor intensive and expensive. Most labs will do an initial analysis with a more relaxed protocol to save time and money. If the results come back low, then some will take additional efforts to ensure accuracy. It is important to recognize that semen analysis – even when performed under careful and well-controlled conditions – can have error of up to 20%. This means that if your sperm count is measured 10 million cells per mL (M/mL), it could really be anywhere from 8 – 12 M/mL. So you need to think of it more as a range rather than an absolute measurement.

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Daily Variations in Sperm Count

A man’s sperm count varies greatly from day to day and week to week. In the short run, much of the variability is due to sample collection and handling. In the longer term, variations can be much larger and can be caused by a number of biological and physical events that impact sperm production – such as having a fever, taking a new medication, or changes in diet.



Variations due to sample collection & handling

If you are interested in seeing trends in sperm count over time, you will want to try to be consistent in the way you collect and handle the semen sample for each semen analysis. Here are the major causes of variation due to sample collection & handling.



There are three important factors during sample collection that can impact test results – abstinence period prior to sample collection, excitement level during collection and how much of the sample gets collected.



1. Abstinence: Abstinence greatly impacts sperm count. Sperm stores are depleted with each ejaculation and take about 2 days to refill. As abstinence period increases, sperm slowly build up. If abstinence is greater than 7 days, sperm begin to die and decompose causing the semen sample to be filled with excess cell fragments and other debris. For this reason the WHO recommends an abstinence period of 2 -7 days. When having a repeat semen analysis performed, you can optimize precision by abstaining for the same amount of time for each test.

2. Method of Collection: Your body can tell when it is “the real deal.” The more excited you are during collection, the more sperm are found in the ejaculate. Some studies have found that samples collected at home where the man is more comfortable have had higher values for sperm concentration, total count and motility. Excitement level during collection is obviously difficult to control but it does contribute to variation of semen analysis results and may be worth taking a mental note.

3. Collecting the Sample: Just be sure the entire sample makes it into the cup. The first few drops of the ejaculate contain the majority of the sperm cells, so missing the first drops can cause lower results. Likewise, the latter part of the ejaculate consists primarily of seminal fluid so if that part is not collected, the result can show up as artificially high.