Background: Renal failure (RF) is a significant health issue with various etiological factors, including environmental toxins. Specific Background: Cadmium (Cd), a known toxic heavy metal, has been implicated in renal damage, while calcium (Ca) levels may also be affected. Knowledge Gap: The relationship between Cadmium and Calcium levels in RF patients, despite the well-established link between heavy metals and renal impairment, remains underexplored. Aims: This study aimed to evaluate changes in blood serum Cd and Ca levels in RF patients and investigate their correlation. Methods: The study, conducted in Iraq from July 2023 to February 2024, involved 150 participants, including 100 RF patients and 50 healthy controls, and used Flame Atomic Absorption Spectroscopy for analysis. Results: The mean Cd level was significantly higher in RF patients (2.30 µg/L) compared to controls (1.44 µg/L, P < 0.05). Conversely, the mean Ca level in RF patients was significantly lower (36.06 mg/dL) compared to controls (51.85 mg/dL, P < 0.05). A significant negative correlation between Cd and Ca levels was found (P ≤ 0.001). Novelty: This study provides novel insights into the detrimental impact of elevated Cd levels on Ca status in RF patients. Implications: The study underscores the necessity of controlling Cd exposure and Ca levels in renal function (RF) management to mitigate its environmental impact on renal health. Highlights: Higher Cd Levels: Increased cadmium in RF patients. Lower Ca Levels: Decreased calcium in RF patients. Negative Correlation: Cadmium inversely affects calcium levels. Keywords: Cadmium, Calcium, Renal Failure, Heavy Metals, Blood Serum