Nephrology

524 Glomerular Filtration Rate

  • Glomerular Filtration Rate 

    Estimated GFR 

    For most clinical purposes an estimate of the GFR can be obtained from the serum creatinine and the height of the child
    GFR (ml/min/m2)  =  40 x height (cm) /serum creatinine (umol/l)
    This formula is valid for children over 3 years old.

    Creatinine Clearance

    This is used to measure GFR but has generally been replaced by the EDTA or DTPA clearance tests or the estimated creatinine clearance (see above).
    Normal values are 80-150 ml/min/m2 (1.3 - 2.5 ml/sec/m2)

    1. No meat for 24 hours before or during collection period
    2. 2. Commence 24 hour urine collection after a discard urine.  Note exact times of voiding discard and final urines.  These need not be exactly 24 hours apart but exact times are needed to determine creatinine excretion.  A special 24 hour collection container is supplied by Biochemistry
    3. Venous blood is taken during the collection for serum creatinine
    4. Record height and weight on request card so surface area can be calculated.

    CHROMIUM EDTA CLEARANCE

    This is used for precise determination of GFR.  It does not involve urine collection and is therefore more accurate than the creatinine clearance.

    Procedure

    The child receives an intravenous injection of 51Cr EDTA and the blood radioactivity is measured at 2 hours and at 4 hours afterwards.  About 4 ml blood is taken at these times for estimation of the T1/2 of the radioactivity from which is calculated the clearance.