Measurement of Renal Function
Lecture given:
Table of Contents
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Objectives
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
WBC
- 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)
Ultrasound
- Most commonly used
- Best way to look for obstruction
- Can use intravenous pyelogram (IVP) to get better image
CT
- Gold standard for stone
- But not useful often due to radiation, but very confirmatory
- Best test to look for kidney cancer
Angiogram
- 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
Indications:
- 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
Contraindications:
- 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
Evaluations:
- Light microscopy
- Immunofluorescence
- Electron microscopy
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page revision: 21, last edited: 23 Apr 2012 04:23