Measurement of Renal Function

Lecture given:


List the various ways glomerular filtration rate can be estimated and the advantages and disadvantages of each test

  • Kidney function: filter blood and clear nitrogenous wastes and preventing specific solutes, proteins and blood cells from being excreted from the body
  • Requires: glomeruli, tubules, interstitium, blood vessels
  • GFR: determine the urinary excretion of a marker substance which is filtered at the same rate as it is excreted
    • Neither absorbed nor excreted by tubules
    • Freely filtered across the glomerular membranes
    • Not metabolized or produced by the kidneys
    • only inulin meets these requirements
  • Renal clearance: hypothetical volume of plasma from which a substance is completely removed per minute in one pass through the kidney. (If that substance is inulin, we call it GFR)
  • Normal GFR is >90mL/min

Describe the value of urinalysis in evaluation of renal pathology

  • the poor person's renal biopsy

RBC present

  • glomerular, cancer, stones
  • NEVER should have RBC in urine


  • UTI (most common), esp with e.coli present
  • Interstitial nephritis

Cast cell full of WBC

  • Interstitial nephritis (AKI)

Cast cell full of RBC

  • Glomerular nephritis

Oxalate crystals
*Possibly normal

Describe the utility of various imaging techniques - Ultrasound, CT, MRI and Nuclear medicine scans in investigating patients with renal disease

Plain Xray

  • calcifications (i.e. stones)


  • Most commonly used
  • Best way to look for obstruction
  • Can use intravenous pyelogram (IVP) to get better image


  • Gold standard for stone
  • But not useful often due to radiation, but very confirmatory
  • Best test to look for kidney cancer


  • Show renal artery stenosis (to also see if need angioplasty)

Nuclear Medicine Tests

  • Radiopharmaceutical agents with specific renal handling characteristics are employed
    • Administered and imaged with gamma camera that records the location and number of counts emitted
    • Permits both estimates of function of an organ as well as anatomic delineation
      • Measurement of renal function (GFR estimate similar to inulin)
      • Measurement of split renal function (individual kidneys)
      • Renovascular disease
      • Disruption of ureteric anastomosis in a renal transplant patient
      • Show area of scar in kidneys

List the indications and contraindications to performing a renal biopsy


  • Cause of renal disease can't be determined by less invasive procedures
  • Signs and symptoms suggest parenchymal disease that can be diagnosed by pathologic evaluation
  • Differential diagnosis includes treatments that have different treatments/prognosis/both
  • Most common biopsy is done in glomerulonephritis


  • Uncooperative patient (need to lie still)
  • Solitary kidney (may bleed and go into failure)
  • Hemorrhagic diathesis
  • Uncontrolled severe hypertension
  • Severe anemia
  • Cystic kidney
  • Hydronephrosis
  • Acute pyelonephritis (may spread infection)
  • Multiple renal artery aneurysms
  • Renal neoplasm (never biopsy! Can usually identify through imaging, remove surgically. If biopsy negative, likely false negative anyway)
  • End stage renal failure (no change in outcome)

Complications: (bleeding)

  • Common: Peririenal hematoma
  • 10%: gross hematuria
  • 1% AV fistula
  • <1% bleeding that requires surgery
  • <0.1% mortality


  • Light microscopy
  • Immunofluorescence
  • Electron microscopy


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