Post on 22-Dec-2015
Assessing the Kidney
The Kidney
The Structure The Function
Structure and function are not completely independentSome tests give information on both aspects
Assessing the Kidney
The Kidney
The Structure
Radiography PlainContrast
Excretory urography (assesses function too)Retrograde urographyComputed tomographyMagnetic resonance imagingUltrasonographyBiopsy (microscopic structure)
Renal Function Tests
The tests may be on Extracellular fluid (blood/plasma as representative of ECF) Glomerular function Tubular function Urine
Analysis of Blood / Plasma
Abnormalities, if due to renal dysfunction may be caused by glomerular or tubular problems
There may be compensation for any abnormalities caused by renal dysfunction
Changes may be due to problems other than renal dysfunction
Analysis of Blood / Plasma
1. Blood urea – excreted by kidney, expected to increase in renal diseasePoor indicator of renal function
May be normal until renal function is severely compromised
Dehydration raises blood urea when kidney function is normal
Depends on the diet (protein)
Analysis of Blood / Plasma
2. Serum creatinineMostly an indicator of glomerular function. Why?Also poor indicator of renal function – non linear relationship with GFR (normal serum creatininedoes not indicate normal kidneyfunction)Useful for monitoring progression of diseaseBUTLittle change with dehydration,DietMostly related to muscle mass
Analysis of Blood / Plasma
3. Serum electrolytesSerum Na+, K+, HCO3-, Ca2+ and Phosphate may be abnormal in kidney disease
Very non specific testMany other factors cause changes in serum electrolytes
Analysis of Blood / Plasma
4. Plasma proteinsRenal disease can cause urinary loss of proteins and lead to low plasma protein levels
Non specific testOther factors cause changes in plasma proteins
Glomerular Function
1. Glomerular filtration rate Creatinine clearance
Most often used indicator of GFR Inulin clearance
Not used clinically, as infusion is needed Urea clearance
A poor indicator of GFR as much reabsorption occurs and at a variable rate
Radionuclide excretion rateNeeds more sophisticated instruments, not routinely used
Glomerular Function
1. Glomerular filtration rate Creatinine clearance
Creatinine clearance may be calculated using a formula that takes into account
Serum creatinineAgeBody weightHeight
Glomerular Function
2. Examination of urine Presence of abnormal constituents
e.g. proteins, if present in significant quantities could have come only from the glomerulus – abnormality of filtration barrier
Red blood cells – abnormal appearance of red cells in urine may indicate they have leaked from the glomerulus
Tubular Function
1. Examination of urine Substances not usually excreted may appear in significant
amounts Renal glycosuria Aminoacidurias
Estimation of 24 hour excretion of normally excreted substances Non specific, as handling of many is influenced by other
factors Changes in plasma levels cause changes in excretion rate
Tubular Function
2. Specialised tests Urine concentration and dilution ability
Water deprivation test Water loading test Plasma and urine osmolality
Urine acidification tests
Examination of Urine
Physical examination Appearance
haematuria Volume
Polyuria, oliguria, anuria Osmolality /specific gravity
Meaningful only with plasma osmolality or if consistently high/low pH
Meaningful only in combination with plasma pH