If a patient has some residual renal function, then the residual renal urea clearance (Kru) can be calculated. This often will decline during to zero in patients being hemodialyzed.



(1) Collect all urine in the interval between the end of one hemodialysis session and the beginning of the next session.

(1a) The patient should void after completion of the completed hemodialysis session and discard this sample.

(1b) All subsequent urine until the next dialysis session should be collected in collection bottle. A small volume of dilute acetic acid (0.1 Normal) or other preservative should be in the collection bottle to reduce bacterial breakdown of the urea during the collection period. The collection bottle should be refrigerated between urine collections.

(1c) The patient should empty the bladder before the next session and add this to the collected specimen.

(2) A plasma urea nitrogen level is collected at the beginning of the collection period (end of the hemodialysis session) and at the end of the collection period (just before starting the next hemodialysis session).


mean plasma urea nitrogen level in mg/dL =

= ((postdialysis plasma urea nitrogen level in mg/dL) + (predialysis plasma urea nitrogen level in mg/dL)) / 2


residual renal urea clearance (Kru) in mL/min =

= (urine volume in mL) * (urine urea nitrogen in mg/dL) / (collection period duration in minutes) / (mean plasma urea nitrogen level)


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