Krueger Test Sperm Function

There are a number of factors to consider when examining the viability of semen and/or sperm. One of them is the shape of the sperm or morphology. Morphology indicates how well the sperm developed in the testicles. The development of sperm in a man’s testicles is called spermatogenesis.

A man whose sperm has maturation defect is likely to have problems with sperm morphology, which in turn, significantly decreases the sperm’s chances of fertilizing his partner’s eggs.

Sperm analysis methods

There are two methods of conducting a sperm analysis:

Clinical labs usually estimate the percentage of sperm that have normal shape in the ejaculated specimen.

Trained technicians in specialized andrology laboratories perform a strict semen analysis known as the Krueger criteria. These "strict criteria" are studied with regards to the success or failure of fertilization.

Fertility potential

The presence of abnormally shaped sperm greatly affects the chances of fertilization. On the Krueger strict morphology analysis, the reduced number of normal-shaped sperm means decreased chances at fertilization success or low fertilization rates.

On the other hand, the reduced number of normal-shaped sperm without Krueger strict morphology analysis may indicate a fertilization problem.

To be sure,  the test should be repeated in a lab that performs Krueger strict morphology analysis. Strict morphology is a useful test to perform with couples that have unexplained infertility, even if the semen analysis and non-strict morphology are otherwise normal.

Strict sperm morphology predicts a man’s fertility potential even though his sperm count, motility and/or regular morphology of the SA are all normal.

Strict morphology

Strict morphology is performed by looking at several individual sperms based on a very rigid set of criteria. This procedure is performed only in specialized laboratories with highly trained technicians.

At 1000x, the sperm are stained and examined under oil for any abnormalities and are also checked for normal size and shape of the head, mid piece and tail. A sperm with even a minor defect in any criteria is deemed abnormal. Very few sperm are considered normal or perfect during a strict morphology test compared to the regular or he "estimated crude morphology."

The result of a strict morphology test indicates and predicts the sperms fertilizing capacity:

  • Strict morphology score over 14 % normal: (normal; fertilizing capacity excellent)

  • Strict morphology score 4-14 % normal: (abnormal; possibly decreased or impaired fertilizing capacity)

  • Strict morphology score 0-3% normal: (abnormal; severe impairment or probable inability to fertilize