Measurement of renal function Flashcards
Clinical Assessment
Look for specific kidney functions which are affected: fluid balance, electrolyte balance, EPO production, Vitamin D3, excretion and acid/base balance
Use of bedside clinical data
Weight and fluid balance charts
Degree of oedema
Dipstick testing
Renography techniques
Gamma camera planar scintigraphy
Positron emission tomography (PET)
Single photon emission computerised tomography (SPECT)
Biochemical data useful for identifying renal impairment
Plasma/serum creatinine
Plamsa/serum urea (blood urea nitrogen)
But these usually only increase after 60% loss in renal function
Normal range of plasma creatinine
40-120 umol/L
What increases plasma creatinine
large muscle mass drugs that interfere with analysis drugs which inhibit tubular secretion ketoacidosis ethnicity
What decreases plasma creatinine
reduced muscle mass starvation/cachexia immobility pregnancy severe liver disease
What is blood urea nitrogen (BUN) increased by
high protein diet hyper catabolic conditions GI bleeding muscle injury drugs (glucocorticoids/tetracycline) hypovolaemia
What decreases BUN
malnutrition
liver disease
sickle cell anaemia
SIADH
What is biochemical data useful for
Identifying renal impairment
Modifying dosages of drugs
Definition of clearance
The volume of plasma completely cleared of a given substance in unit time
What does clearance tell us about
Filtration
Reabsorption
Secretion
But nothing about precise tubular sites
Equation for clearance
{U(x) x V}/P(x)
Best substance for measuring GFR (and drawbacks)
Inulin
But - must be administered by IV to get constant plasma or serum levels
Instead creatinine is used
Creatinine problems
Some is secreted at PT (over-estimation by 20%)
Colorimetry methods used - Jaffe method (under-estimation by 20%)
Venous blood and urine samples needed
Can be different with muscle diseases/damage or having eaten lots of meat - 24 hour sample is best
eGFR
Different equation taking into account age, mass and plasma creatinine - and a multiplier
Called modification of diet in renal disease
PAH to measure renal blood flow
Para-aminohippuric acid
Not normally present in blood
90% cleared from kidney in one passage
Some filtered, remainder secreted at PT & 10& bypasses tubule - not secreted at all
Blood and urinary markers of early stage kidney disease
Kidney injury molecule 1 IL 18 Fatty acid binding proteins Neutrophil gelatinise associated lipocalin Cystatin C
