Creatinine

The concentration of creatinine in the plasma of a healthy person is relatively constant
and its sharp fluctuations do not depend on the amount of fluid consumed, exercise, and urine excreted.
Therefore, an increase in creatinine in plasma is always a sign of reduced glomerular filtration and impaired kidney function.
Creatinine clearance is also a suitable factor for estimating glomerular filtration rate (GFR)
and, as a result, better diagnosis of kidney diseases and assessment of kidney function.
For this purpose, serum creatinine and 24-hour urine are examined simultaneously.

Uric Acid 

Uric acid and its salts are the end products of the purine metabolism.
The most important disease caused by increased uric acid is gout,
in which increased uric acid causes the formation of monosodium urate crystals around the joints.
High levels of uric acid are also considered an indirect risk factor for coronary heart disease.
Factors such as kidney disease, impaired renal filtration, alcohol use, starvation, and the use of some drugs can cause increased uric acid.
Decreased uric acid levels are rarely seen in inherited metabolic disorders.

Urea

Urea is the nitrogenous end product of protein catabolism. The increase of urea in the blood is related to istemia or hyperemia.
Urea and creatinine levels are determined simultaneously to distinguish between pre-renal and post-renal hypothermia.
Pre-renal hypothermia occurs as a result of increased protein catabolism, dehydration, cortisol treatment,
and decreased renal filtration, causing an increase in urea levels, while creatinine levels remain within the reference range.
In postrenal asthma caused by urinary tract obstruction, both urea and creatinine levels increase. Of course, creatinine increases to a lesser extent.
In kidney diseases, urea concentration increases due to reduced glomerular filtration or absorption of more than 200 grams of protein per day.