renal disease Flashcards
prevalence of kidney disease
Up to 10% pop have some aspect of kidney disease
it is part of other conditions - HTN, dm
UTI
o Really common o Kidney tract problem o Usually just infection in bladder o E coli bacteria line bladder wall Lifetime risk for females 10-30% • Lead to 3 million GP visits per year in UK
ways renal disease can present
• Haematuria • Proteinuria • Nephrotic syndrome • Nephritic syndrome • Hypertension • Acute kidney injury • Chronic kidney disease Urinary tract infection • Abdominal pain • Complications of hypertension (esp malignant hypertension) • Oliguria or anuria • Polyuria, nocturia - often a metabolic problem – nothing wrong with kidneys
how long are the kidneys
about 3 vertebral bodies
dark white in kidney in CT
excreting contrast in collecting system
summarise anatomy of the kidney and tubule
• Glomerulus fed by arteriole – comprises of capillary tuft
o Blood leaving glomerulus is blood supplies around tubules
o Filtrate goes through the tubules
o Cortex contains glomerula
o Medulla – loop of henle and collecting duct
what is the renal parenchyma made of
cortex and medulla
summarise the anatomy and the function of the glomerulus
it is the filtering unit of the kidney
blood enters cap tuft through afferent arteriole
under high pressure the fluid is pushed out of the blood vessel - ceels and proteins are retained in the capillary lumen
specialised filtration to allow this:
Endothelial cell layer of capillaries has pores
–Glomerular basement membrane
–Epithelial cells (podocytes) with slit membranes
blood leaves glomerulus by efferent arteriole
filtrate passes into Bowman’s capsule and into tubule,
becoming urine
role of podocytes
allow you to filtrate the blood but maintain blood cells and protein in blood
functions of the kidney
Filtration and excretion of waste products
Electrolyte homeostasis
Blood pressure control via renin/angiotensin/aldosterone axis
prostagladins and bradykinin
Acid Base homeostasis
what hormones does the kidney produce
Erythropoietin (epo) – red blood cell production
1,25 Calcitriol (active vitamin D) – calcium, phosphate and
bone metabolism
what are the manifestations in patients when kidney function goes wrong
anaemia - because not making epo, cause fatigue acidosis bone fractures poor clearance of waste = fatigue reduced excretion of many drugs electrolyte abnormalities eg high potassium, low calcium, low or high sodium… impaired fluid balance high blood pressure
treatability of manifestations of when kidney func goes wrong
anaemia - treatable with epo replacement
acidosis - treatable with bicarbonate
bone fractures- treatable by lowering serum phosphate,
replace active vitamin D, suppress PTH
poor clearance of waste - when v poor only
replaceable by dialysis or a transplant
reduced excretion of many drugs - avoid nephrotoxic
drugs and amend drug doses
electrolyte abnormalities - need correcting
impaired fluid balance - oedema usually (excess fluid)
high blood pressure - needs treatment
why not just use creatinine to assess kidney ‘cleaning’ func
a product of metabolism of muscle creatine and
phosphocreatine – so muscle mass make big diff to blood creatinine levels
sex difference
so having same blood creatinine doesnt mean have same kidney function
Freely filtered and not reabsorped but there is tubular
secretion
what is glomerular filtration
Most common test of kidney function
• Determines the clearance of a substance from the plasma
• Does not determine the cause for kidney disease
what is GFR
• Sum of the filtration rates of all functioning nephrons
• Normal 120-130ml/min/1.73m2
• Depends on age, sex, body size, muscle mass
• Reduced GFR means loss of filtering capacity and
accumulation of waste products
how do you measure GFR
No direct measurement
• Estimated from urinary clearance of an ideal filtration marker
from the plasma per unit time
what is an ideal marker for measuring GFR
freely filtered solute, not secreted or
reabsorbed by the kidney, not metabolised by the kidney
ie it is only removed from the body by the kidney - see how fast this happens
markers used for measuring GFR
• Inulin – best molecule, but too complex to use in practice - not used Radioactive markers (eg EDTA, iothalamate, iohexol) – expensive, low dose radioactivity, takes 2-4h and iv injection, need blood test, or radioactive body count? - cant do it regularly Creatinine – good endogenous substance • Cystatin c – probably best marker but not widely available - not affected by muscle mass
summarise eGFR
GFR determined from serum Creatinine or Cystatin C is an
ESTIMATED GFR
how is creatinine used to determine eGFR
Used to be common to collect 24 hour urine samples to
measure Creatinine clearance as measure of GFR (from urine
creatinine, serum, urine volume)- not now (– difficult to do – people forget some samples)
based on mathematical eqn
Cockcroft Gault: includes body weight and creatinine
eGFR from MDRD or CKD-EPI or other Equations: uses serum
creatinine and age only
problems with eGFR
still uses creatinine
Only relevant in stable patients, not for AKI, dependant on
muscle mass
USEFUL if have serial measurements
urine dip
helps tell where the problem is and guides investigations Especially if protein or blood bedside investigation
causes of red/brown urine
– myoglobinuria (from rabdomyolysis - muscle crushing trauma) or haemoglobinuria
– food dyes or beetroot ingestion
– porphyria
– rifampicin
causes of white urine
pyuria, phosphate crystals, chyluria
causes of black urine
haemoglobinuria , alkaptonuria
what does proteinuria indicate
glomerular problem/damage (usually)
Can be a benign variant (Orthostatic proteinuria)
how do you assess proteinuria
urine dipstick tells you that it is present
need to quantitate
spot urine Protein:creatinine ratio (PCR) or
albumin:creatinine ration (ACR)
?? normal up to 30 - low level protein excretion
what is AKI
A rapid decline in renal function over hours or days
with:
Accumulation of (nitrogenous) waste products
Potentially life threatening metabolic consequences
With or without reduction in urine output.
definition of AKI
Serum creatinine rise by greater than 26 umol/L within 48 hrs
OR
Serum creatinine rise 1.5 x from the reference value which is
known or presumed to have occurred within one week
OR
Urine output is less than 0.5ml/kg/hr for 6 consecutive hours
what reference serum creatinine should be used
lowest creatinine
value recorded within 3 months of the event
