Laboratory investigations are essential for the early detection, diagnosis, and monitoring of kidney diseases. Serum creatinine is one of the most commonly used biochemical markers for evaluating renal function. It is used in validated equations to estimate the glomerular filtration rate (eGFR), which reflects the kidneys’ ability to filter waste products from the blood. However, creatinine concentrations can be influenced by muscle mass, age, diet, and other clinical factors. Cystatin C is another important biomarker used to estimate glomerular filtration rate. Because it is less dependent on muscle mass than creatinine, it can provide additional information when creatinine-based estimates may be less reliable. In appropriate clinical settings, combining creatinine and cystatin C improves the accuracy of kidney function assessment. Urinary albumin-to-creatinine ratio (UACR) is particularly important for detecting early kidney damage. Increased urinary albumin excretion may indicate glomerular injury, even when eGFR remains relatively preserved. Urinalysis also provides valuable information through the detection of protein, blood, abnormal cells, and urinary casts. Al-Mustaqbal University The First University in Iraq