Assessment of kidneys & urinary tract

GFR is low in newborn & esp low in preterm
1. GFR @ 28 weeks' gestation =10% of term infant
2. in term infants corrected GFR (15-20 ml/min per 1.73m2) rapidly rises to 1-2 years old when adult rate (80-120 ml/min per 1.73m2) achieved
plasma creatinine conc (PCr)
1. main test of renal function
2. rises progressively throughout childhood accord to height & mm bulk
3. may not be outside lab 'normal range' until renal function has dropped to < 1/2 normal
estimated glomerular filtration rate (eGFR)
1. =k x height (cm)/ creatinine (micromol/L)
  1. k= 40 (Cr measured using Jaffe method) or 30 (Cr measured enzymatically)
2. better measure of renal func than creatinine
3. useful to measure renal func serially in kids w/ renal impairment
insulin or EDTA GFR
1. more accurate
  1. clearance from plasma of substances freely filtered @ glomerulus, is not secreted or reabsorbed by the tubules
2. use limited in kids
  1. need for repeated blood tests
creatinine clearance
1. requires timed urine collection & blood tests
2. rarely done in kids
  1. because inconvenient & inaccurate
plasma [urea]
1. increased in renal failure often before Cr starts rising
2. raised levels may be symptomatic
3. increased by high protein diet & if in catabolic state
radiological ix
1. ultrasound
  1. standard imaging procedure
  2. provides anatomical not functional assessment
  3. great @ visualising urinary tract dilatation, stones & nephrocalcinosis (small multiple Ca deposits in renal parenchyma)
  4. adv: non invasive, mobile
  5. disadv: operator-dependent, won't detect all renal scars
2. DMSA scan (99mTc dimercaptosuccinic acid)
  1. static scan of renal cortex
  2. detects functional defects like scars
  3. v sensitive
    1. need to wait minimum 2 months after UTI to avoid diag of false 'scars'
3. micturating cystourethrogram (MCUG)
  1. can visualise bladder & urethral anatomy
  2. detects vesicoureteric reflux (VUR) & urethral obstruction
  3. disadv: invasive & unpleasant ix esp beyond infancy, high radiation dose
4. MAG3 renogram (mercapto-acetyl-triglycine, labelled with 99mTc)
  1. dynamic scan
  2. isotope labelled substance MAG3 secreted from blood into urine
  3. measures drainage
  4. best performed w/ high urine flow
  5. in kids old enough to cooperate (usually >4 years), scan during micturition is used to ID VUR
5. plain abdominal x-ray
  1. IDes unsuspected spinal abnormalities
  2. may ID renal stones
  3. poor at showing nephrocalcinosis

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Assessment of kidneys & urinary tract

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	Created by v.djabatey almost 11 years ago