Functional examination of the kidneys

Examination of serum creatinine concentration

 * Norm: 50–100 μmol/l.
 * When kidney function is impaired, the serum concentration of creatinine increases.
 * In some patients, even with impaired kidney function, the serum creatinine concentration may be within the reference limits - it depends on the production of creatinine by the skeletal muscle.


 * Clearance of creatinine Ckr:


 * Ckr expresses how the plasma is purified from the monitored substance;


 * $$C_{kr} = \frac{U \cdot V}{P}$$


 * U = concentration of substance in urine, V = volume of urine per time unit, P = concentration of substance in plasma;


 * normal values: 1.5 to 2.2 ml/s;
 * depends on age, gender and weight.
 * Accurate collection of urine after 24 hours is necessary.

Examination of the concentration ability of the kidneys

 * We find out the ability of the kidneys to create concentrated urine.
 * We monitor urine osmolality. (in a healthy person; osmolality = 600–800 mmol/kg H2O = 500–1200 mOs/kg; without fluid intake = 1200–1400 mOs/kg).
 * This ability is often impaired already at the beginning of kidney disease.

Concentration test - by thirst

 * For 36 hours, the patient must not drink or eat food with a large amount of water.
 * After 12 hours, urine is collected at 4-hour intervals, we determine density and osmolality.
 * Before the last sample, we will take blood - concentration index.
 * We will stop when it reaches the limit given for a certain age.

Adiuretin test

 * It is much gentler, does not burden the patient as much.
 * After a dinner without liquids, when the examinee no longer drinks in the evening, we apply ADH into the nose in the morning (he must not have a cold).


 * Concentration disorders - mainly in diseases of the tubules and interstitium, in case of a violation of the gradient.

Investigating dilution functions

 * We monitor how the patient reacts to increased water intake:
 * In a healthy person, there will be an increase in urine volume, a decrease in ADH production, and thus an increased diuresis and a decrease in osmolality.
 * ADH secretion increases in patients with kidney failure.
 * This method is important in the investigation of water metabolism disorders.

Related Articles

 * Urine examination
 * Glomerular filtration test
 * Clearance