Urea is a waste product produced during protein metabolism and is commonly found in the blood. The kidneys filter urea from the blood into the urine, making it an important marker for kidney function. A urea test is often used to assess how well the kidneys are working, with elevated levels of urea in the blood potentially indicating impaired kidney function.

However, elevated urea levels can also result from other factors, such as consuming large amounts of protein or dehydration. On the other hand, low urea levels may suggest liver failure, malnutrition, excessive hydration, or a low-protein diet. Therefore, urea levels should be interpreted in the context of other clinical factors to determine the underlying cause.

Creatinine is a breakdown product of creatine phosphate, which is found in muscle. Serum creatinine serves as an important indicator of renal health, as it is an easily measured by-product of muscle metabolism that is excreted unchanged by the kidneys.

Elevated serum creatinine levels can result from various lifestyle factors, including the consumption of creatine supplements, high amounts of animal protein, or high-intensity exercise. Other causes may include impaired kidney function. Conversely, low serum creatinine levels can indicate efficient kidney function. Additionally, a low-protein diet or reduced muscle mass may also contribute to lower readings.

The estimated glomerular filtration rate (eGFR) is one of the best tests for assessing kidney function. The kidneys contain thousands of glomeruli, which act as tiny filters that remove waste from the blood. eGFR estimates how much blood passes through these glomeruli each minute and is calculated based on blood creatinine levels, gender, age, and weight. A high eGFR indicates optimal kidney function, while a low eGFR suggests that the kidneys may not be working at full capacity and could be a sign of kidney disease.

eGFR is also a valuable tool in determining the stage of kidney disease, helping to identify the most appropriate treatment. Early detection increases the chances of slowing or stopping disease progression. However, a low eGFR may also be observed in individuals from certain ethnic backgrounds or those with increased muscle mass, in which case it may not necessarily indicate impaired kidney function.