A kidney is an important organ in the human body, the body will have problems if the kidney does not work properly. Treatments for the disease may include hemodialysis. Hemodialyzed Patients often have high creatinine, urea, and uric acid levels. This condition may affect the quality of laboratory results. According to The Beer-Lambert’s Law, the portion of the light absorption will depend on how many molecules interact with it. However, the theory cannot be applied to a solution with high concentration. This condition can trigger inaccurate results which may be harmful to the patients because it can cause errors in diagnosis, treatment, and disease monitoring. This condition can be handled by diluting the concentrated serum. A serum sample was diluted with a physiological saline solution (NaCl). This study aims to determine the level of kidney function test in hemodialyzed patient’s serum with and without dilution. This research was Pre-experimental Design methods with One-Group Pretest-Posttest Design. The research sample was used serum of hemodialyzed patients with creatinine level of more than 10 mg/dL, urea level of more than 256 mg/dL, and uric acid level of more than 12mg/dL, amounted to 40 samples. The test results were analyzed descriptively and statistically using Paired Sample T-Test. The mean of creatinine and uric acid levels increase 2.29 mg / dL (16.72%) and 4.02 mg / dL (44.47%) respectively, while the mean urea decrease 19.52 mg / dL (6.38 %).The results tested with Paired Sample T-Test showed a significant 0.000 (<0.05) which means there was a difference in kidney function tests in hemodialyzed patients with and without dilution.