Urine Output
< 2ml/kg/hr - False
A urine output of less than 0.5 - 1.0 ml/kg/hr indicates renal insufficiency.
This figure must however be taken in the context of the fluid status of the patient. A
child who is dehydrated with normal renal function may produce relatively small quantities
of urine and would be said to be in a state of prerenal failure. If fluid is not
administered, so-called "acute tubular necrosis" may result.
Raised serum creatinine - True
Creatinine is a product of muscle metabolism and is produced at a constant rate, proportional to
muscle mass. It is freely filtered by the kidneys and therefore the clearance of
creatinine is inversely proportional to the serum concentration.
An estimate of GFR is given by the Schwartz formula:
GFR (ml/min/1.73m2) = 40 x Height (cm) / Creatinine (µmol/l)
Raised glomerular filtration rate - False
The
glomerular filtration rate (GFR) is the amount of blood which is completely cleared of a
substance which is freely filtered by the kidneys, per unit time. The normal units
are mls/min and the value is then corrected for body surface area and described as
mls/min/1.73m2.
Creatinine is used as a measure of GFR in that it is freely filtered, although it is also secreted
into the urine through the proximal tubule and therefore at a low GFR, creatinine clearance will over-estimate GFR.
Normal values for GFR are > 80 mls/min/1.73m2
Reduced serum urea
- False
Urea is produced by the liver as a result of protein metabolism. It is excreted by the
kidneys and therefore serum levels will rise in renal failure.
However urea levels will rise independently of renal function in the presence of dehydration or
increased protein breakdown, which occurs in children with an inadequate calorie intake
and who start to break down body protein.
Hyperkalaemia
- True
Potassium levels are increased in renal failure as the kidneys are responsible for potassium
excretion.
Hyperkalaemia is discussed later on in the program.
If you wish to go straight to the page on hyperkalaemia click here. (Click on the "Back" button in the top left of the web browser to subsequently return
to this page).
Hypercalcaemia - False
Calcium levels are usually reduced in renal failure. This primarily results from a decreased
excretion of phosphate which leads to a rise in serum phosphate levels. The levels
of phosphate and calcium are inversely related and as phosphate goes up, calcium levels
must drop, otherwise crystals of calcium phopshate will start to be deposited in tissues.
In most cases of ARF, hypocalcaemia is not a clinical problem and calcium should only be
administered if symptomatic eg. tetany, seizures.
Hyperphosphataemia - True
Phosphate levels rise in ARF as a result of decreased excretion.
Acidosis - True
The kidneys are responsible for excreting hydrogen ions and ARF is associated with metabolic
acidosis:
Decrease in pH; decrease in serum bicarbonate; decrease in pCO2.
Acidosis is discussed later on in the program.
If you wish to go straight to the page on acidosis click here. (Click
on the "Back" button in the top left of the web browser to subsequently return
to this page).