renal function Flashcards
how much fluid is filtered in the kidneys per day
180 L/day of water + electrolytes and amino acids
178.5L is reabsorbed - all glucose and amino acids are reabosrbed and most sodium and chloride reabsorbed
what are the main parts of the nephron
renal corpsucle (glomerulus and bowman’s capsule) and a renal tubule
1-1.5 million nephrons per kidney
what are the two types of renal function test categories
glomerular function tests, tubular function tests
what are the different types of function tests
clearance test, serum creatinine, serum urea, glomerular filtration rate, urinalysis
what may be the first signs of renal damage in a patient?
low levels of albumin in urine
write about clearance tests
most common = CrCl and inulin( gold standard). calculated with the formula U.V/P
U: conc of analyte in urine mmol/L
P: conc of substance in plasma mmol/L
V: volume of urine per unit time ml/min
how does the patient prepare for clearance tests?
- accurate urine collection over 24hrs
- no high protein meals before test (can impact Cr levels)
- stop medication use if able (NSAIDs)
- ensure hydration
- ensure normal fluid intake
how is urine collected for CrCl tests
- begin in morning after first urination (build up of wastes in this sample)
- record exact time when collection starts- collect all urine 24hrs
- ensure refrigeration of sample
- stop exactly 24hrs after
why is serum collected alongside urine
for comparison between Cr in blood v urine
what are the units of CrCl
urine vol measurement in mL, creatinine conc in urine/blood in mmol/l or mg/dL
what is eGFR
describes the flow rate of filtered fluid through the kidney
what two equations can be used for eGFR calculations
Cockcroft Gault and Modification of Diet in Renal Disease
write Cockcroft Gault and Modification of Diet in Renal Disease equations
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ref ranges for sCr?
men: 62-115 umol/L
women: 53 to 97 umol/L
how is creatinine formed
creatine produced in liver + pancreas… creatine kinase phosphorylates creatine to form creatine phosphate (energy for muscle cells)
creatinine is a breakdown product of creatine phosphate from muscle metabolism and is formed at a constant rate
what assay can be used to detect creatinine
Jaffe assay - where creatinine + alkaline picrate —–> alkaline creatinine picrate complex
*this assay is sensitive to changes- can be influenced by chromagens i.e pyruvic acid
what is modified Jaffe procedure
measures absorbance of reaction mixture at two diff pHs- acetic acid added for the second reading which removes colour produced by creatinine- colour produced by contaminants not removed
calculate creatinine absorbance by subtraction
what can affect creatinine levels in the body?
intake of cooked meat (up), intake of protein/creatinine supplements, intense excersise, dehydration
what is the normal urea:creatinine ratio
between 10:1 and 20:1
increased ratio: ;low muscle mass, GIT bleed, burns
decreased: severe liver disease, decreased protein intake
serum urea ref range?
1.7-8.3 mmol/L
what is urea
nitrogenous end product of protein - comes from deamination of proteins to form ammonia which is converted into urea
is urea filtered by glomerulus
yes but some is reabsorbed with water and returned to the blood
how is urea measured
measured indirectly via quantifying nitrogen content of urea - urease enzyme used in hydrolysis
*ammonia is formed from the alkalinisation which is then used in assay procedures
describe nesseler’s reaction
ammonia formed in urease reaction mixed with nesseler’s reagent forms brown product
nesseler’s reagent = iodine salt of mercury + potassium
