In this study, it is considered that bioaccumulation should be statistically significant if Cmax of anti-Xa are increased by at least 20%. Estimation of the population size was performed using information obtained from Mahé et al. due to the similar nature of the population studied. As for mean plasma anti-Xa peak levels, a study done by Bara L et al. showed that 431 patients receiving 3 500 IU of tinzaparin for thromboprophylaxis had a mean of 0.15 IU/ml, which is the dose that will be given to most of the subjects in the present study. Based on the coefficient variation of Mahé et al. of 0.36 and the mean plasma anti-Xa level found by Bara L. et al, a standard deviation of 0.05 IU/ml was established, considering that the same coefficient of variation should be maintained across the dose administered. For the purpose of this study, researchers presumed an identical variance between all anti-Xa levels regardless of the day of blood sample collection. According to the null hypothesis, the mean of the distribution is 0.15 IU/ml while for the alternative hypothesis; the average would be 0.18 IU/ml (since established cut-off is a 20% increase). With a paired one-tailed t test, an alpha error of 0.05, a power of 0.90, and a strong correlation between measurements (r=0.7) , 25 participants are required to detect an increase ≥ 20% in anti-Xa activity between sampling on day 2 or 3 and at maximum of 8 days.