Many people who receive a kidney transplant develop problems with how their body processes sugar (glucose). This includes conditions like prediabetes and diabetes, which can lead to more health issues, such as heart problems and infections. One of the main medications used after a kidney transplant, called tacrolimus, can contribute to these sugar problems. Tacrolimus helps protect the new kidney, but it can also harm the cells in the pancreas that produce insulin, a hormone that controls blood sugar. Other factors, such as stress on the body and insulin resistance, can make things worse. The effect of tacrolimus on blood sugar may depend on how the body processes the drug. Some people break down tacrolimus quickly (fast metabolizers), so they need higher doses to reach the right level in their blood. Others break it down more slowly (slow metabolizers) and require lower doses. Doctors can measure how fast someone metabolizes tacrolimus using aparameter called the concentration-to-dose (C/D) ratio. This study aims to find out what increases the risk of developing blood sugar problems after a kidney transplant. It will focus on how quickly patients process tacrolimus and whether this affects their risk of developing diabetes. The study will also look at how common these issues are in kidney transplant patients in Poland.