Kruger morphology predicts outcome of sperm penetration assay: true or false?

Abstract

Objective: To assess the ability of Kruger morphology to predict the outcome of the Sperm Penetration Assay (SPA). Design: Sperm Capacitation Index (SCI) and Strict Kruger morphology have both been proven to correlate with in vitro fertilization rates. Each of these tests has been utilized to direct patient management. However, the correlation between these two tests has never been clearly established. We hypothesized that Kruger Morphology is predictive of SCI outcomes, as smaller studies have demonstrated this correlation. A retrospective review using univariate and multivariate analysis, T-tests, and logistic regression was performed to examine the correlation between all semen parameters and the results of the Optimized Zona-Free Hamster Egg Sperm Penetration Assay (O-HESPA). Materials/Methods: A retrospective review of 115 patients who underwent semen analysis with Kruger morphology and O-HESPA between 1997–2000 was performed. All semen analyses were performed by one andrologist, all O-HESPA and SCI studies were performed by the same reference laboratory. Routine semen analysis included: total sperm count, motility, viability, and Kruger morphology. The Log of the count and % viability were used in the analysis. The significance of Kruger morphology was assessed as a continuous variable and as a discontinuous variable designated as: very poor (0–4), abnormal (5–13), and normal (≥14). SCI was recoded into a dichotomous variable classifying SCI as either a normal (10) or abnormal (≤10). Student’s t-test and logistic regression was performed analyzing Kruger, count, and viability and their relationship to SCI result. Results: When univariate analysis was performed there was a statistical significance between SCI and sperm count (p = 0.001), sperm viability (p = 0.040), and Kruger morphology (p = 0.031). Multivariate analysis found statistically significant correlations between SCI and sperm count (p = 0.002) and sperm viability (0.051). However, the significance between Kruger morphology and SCI was lost (p = 0.128). When SCI was analyzed as a dichotomous variable, 57 patients were identified as having a SCI ≤ 10, and 58 patients with SCI >10. Logistic regression was performed on the SCI results, using log count, Kruger morphology quartiles, and log viability. Log of sperm count was found to be the only variable with statistical significance with respect to SCI results (p = 0.001). Conclusions: Although we had hypothesized that Kruger morphology would be predictive of SCI results, after performing comprehensive statistical analysis, no such correlation was found. T-tests and univariate analysis shows a significant correlation between sperm count, viability and Kruger morphology as they relate to SCI. Logistic regression or multivariate analysis demonstrated that the significance between sperm count and its relationship with SCI still existed. This study found that Kruger morphology could not be used in lieu of SCI. Surprisingly, we found that as sperm count increases the likelihood of a normal SPA increases. This study demonstrates that Kruger morphology assessment cannot be utilized to predict the results of or replace SCI in the management of the infertile couple. Supported by: Male Reproduction Special Funds. Department of Urology, Beth Israel Medical Center.