Ambard's Constant

AMBARD'S CONSTANT (Ambard; method of the glomerular index of urea function) is the regular relationship between the amount of urea excreted in urine during a specific time and the amount of urea present in the blood at the same time. The determination of A. k. is performed in the following sequence: at 8 a.m., the patient urinates, but the urine excreted is not examined; for determination, urine collected exactly 2 hours later is used. Around 9 a.m., 10 cubic centimeters of blood are taken from the patient to determine urea by one of the common methods (van Slyke and others). The calculation is performed according to the formula: ,/-jo. 70.^ 'r. s where Vr is the urea content in the blood in grams per liter, D is the absolute amount of urea excreted in urine in 24 hours. For quick calculation, the amount of urine excreted in the two-hour portion is multiplied by 12 and by the obtained concentration of urea; c is the concentration of urea in urine in grams per liter; r is the weight of the subject being tested, adjusted to normal weight of 70 kg. In a healthy subject, Ambard's constant usually fluctuates between 0.06 and 0.08, and the more the kidney function is impaired, the greater Ambard's constant.