[Plasma urea along with every plasma creatinine test?].

The concentration of plasma creatinine and the estimated glomerular filtration rate, calculated from plasma creatinine, age, weight, and gender, are used to assess kidney function. In routine clinical practice the concentration of plasma urea is often determined at the same time as the creatinine concentration. Urea is a waste product of the breakdown of amino acids and is excreted by the kidneys. Thus reduced kidney function results in a rise of blood urea. In addition, the urea concentration is determined by protein supply and catabolism. The sensitivity and specificity of urea in the diagnosis of kidney dysfunction are therefore low. In only a limited number of cases might measuring urea be helpful in determining the cause of reduced kidney function.