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
berthelot reaction
ammonia from urease reaction reacts with phenol and sodium hypochlorite to for blue indophenol
sodium nitroprusside serves as a catalyst
urease GLDH assay
urease produces ammonia. ammonia is used with NADH to produce glutamate with 2NAD+ by use of glutamate dehydrogenase
what is rapture of the deep
nitrogen narcosis= inhalation of compressed inert gas causes change in conciousness and neuromuscular function
what causes elevated uraemia pre renal causes
pre renal causes: rapture of the deep, low bp (shock, haemorrhage, dehydration), decreased blood flow to kidneys (heart failure, atherosclerosis), increased dietary protein/ protein catabolism
uraemia: renal causes
kidney disease (nephropathy) decreased glomerular filtration i.e nephritis, nephrosis
kidney failure (CKD)
uraemia post renal causes
urinary outflow obstruction such as calculi, tumours of the bladder/prostrate or a severe infection
decreased urea pre renal causes
liver disease (impaired urea synth), high fluid intake (diliution) malnutrition/decreased protein intake
anabolic states (pregnancy, growth, surgery)
increased protein synth = decreased urea formation
define proteinuria
presence of protein in urine, i.e albumin which should not be filtered by the kidneys
proteinuria ref range?
24hr collection: 30-300mg/24
spot urine: 20-200 mg/L
renal tubular function tests
specific proteinuria (globulins)
osmolarity measurements in plasma and urine
water deprivation test
acid load test
describe specific proteinuria
B-2-microglobulin is part of the MCH and is filtered by kidneys and reabsorbed by tubules. large amounts of B-2-microglobulin = indictive of kidney tubular dysfunction
detected via immunological techniques
acute renal disease
failure of renal function over period of hours or days (rising serum urea and creatinine)
can be pre-renal, renal or post renal. necessary to identify quickly
chronic renal failure
progressive irreversible destruction. treat with dialysis or transplant
