Disorders of Renal Function Flashcards
Define plasma and serum
plasma: fluid surrounding blood
serum: fluid remaining after clotted cells removed
What is hypovoloemia?
volume depletion, decreased intravascular volume to salt and water or blood loss
What is the Gold Standard?
reference method against which other methods are compared
What is standardisation?
to conform to a standard (e..g. all routine methods standardised against the gold standard)
What is tumour lysis syndrome?
potentially life threatening condition that occurs usually during cancer treatment of blood tumours due to rapid cancer cell death, leading to toxic levels of cellular material.
What is an MI?
heart attack due to death heart tissue not receiving enough blood/oxygen
What is meant by nephrotoxic?
substance that is damaging to the kidney
What are some non-biochemical tests to asses the renal and urinary system?
patient history, physical examination, urine for culture/sensitivity (UTI), imaging, renal biopsy (invasive)
What are biochemical tests crucial for?
detect renal dysfunction
indicate extent of severity
monitor disease progression
What is AKI?
acute kidney injury
causes include hypovoloemia, renal stones/obstruction, medications, infections, TLS’s, renal insult on top of CKD (many causes)
What is CKD?
chronic kidney disease
causes: diabetes, CVD, hypertension, others
What are the features of an ideal biochemical marker for renal disease?
simple quick to analyse widely available cheap undetectable/stable in health correlates with degree of disease accurate reflection of changes in disease detects AKI/CKD early applicable to all groups in society (age, gender, ethnicity)
What is the glomerulus and its function?
part of the nephron - interfact between blood plasma and kidney
filters blood
The rate at which kidneys filter blood is defined as the
glomerular filtration rate
What is the equation to calculate GFR and hence clearance (you’re gonna have to rearrange)
GFR*plasma = urine * rate of urine formation
clearance or GFR = urine*rate of formation/plasma
What is clearance?
volume of blood plasma from which a substance is completely removed by GFR/time
(note: volume not amount of plasma passing through kidney as substance not removed by single pass through kidney)
What is inulin?
a non-endogenous fructose polymer
How is inulin used as a marker?
administered intravenously, is freely filtered - measured in urine and then GFR calculated using:
GFR = (inulin in urine)*rate of urine formation/inulin in plasma
Used as the gold standard - annoying to do in practice due to IV
What is an issue of creatinine clearance as a marker?
Active creatinine secretion into urine occurs which can slightly overestimate GFR
What are some general issues with creatinine clearance measurments?
urine collection - inaccurate, inconvenient, slow
based on four measurements (urine and serum creatinine, time, volume) each with their own inaccuracy
How are single plasma creatinine measurements used to estimate GFR?
Creatinine concentration in blood is inversely proportional to it’s clearance (inverse standard curve)
can be used to infer clearance and GFR
What are the advantages of using a single blood measurement of creatinine?
creatinine levels fairly constant in adult life
as good as urine clearance measurements
detects renal disease
quick
better than urine clearance to follow disease progression
What are the disadvantages of using a single blood measurement of creatinine?
creatinine is a muscle produced compound - levels reflect renal clearance and muscle production
lower in children and women, and people with low muscle
higher in men, bodybuilders, athletes, people with high meat intake, or those taking supplements
need to use different reference ranges
What is regression analysis
an equation that predicts GFR using creatinine levels and other metrics
What is the issue with Cockcroft-Gault’s equation?
Uses old methods
overestimates GFR at low levels - falsely reassuring
What is the issue with MDRD equation?
imprecision, underestimates GFR at high levels
doesn’t consider body weight
What are the advantages of the MDRD equation?
allowed for standardisation
validated for CKD staging
uses only one biochemical marker (creatinine)
Why is the CKD-EPI equation used clinically?
superior than MDRD - shows less deviance
What is an issue with the CKD-EPI equation?
doesn’t consider ethnicity (which is difficult to define using a computer system)
What are issues with estimating GFR using single blood measurements?
based on creatinine as a filtration marker
age, gender, ethnicity only account for some non-kidney reasons for disease
derive average relationship between variables (there will always be outlying patients)
What are the 2 radiolabelled substances that can be used as markers - outline process?
51Cr-EDTA, 125I -iodothalamate
injected, blood samples taken at regular intervals over short period, GFR calculated from rate of disappearance
not convenient, useful in children (chemo), timed urine not needed
What is urea?
Less toxic product of ammonia which is produced by protein catabolism (liver) and excreted in the urine (kidney)
When GFR is low, urea levels….
increase
If urea and creatinine are both high it means…
high chance of AKI and CKD
Reasons for urea being significantly higher than creatinine are:
higher protein turnover
increased kidney reabsorption
Why might kidney reabsorption of urea be increased?
reduced blood flow
outflow obstruction
What might be a reason for increased protein turnover leading to high urea?
gastrointestinal bleed leading to blood in the stomach (blood meal)
What is cystatin C?
cysteine protease inhibitor synthesised by all cells
Why is cystatin C a good marker?
unaffected by muscle mass, diet, gender
freely filtered
levels increase and GFR drops
more accurate and reliable than creatinine
What is NGAL?
neutrophil gelatinase-associated lipocalin
Why is NGAL used as a test?
BGAL released due to tissue inflammation and injury
so high NGAL in blood or urine indicates insult to kidney as a result of inflammation (AKI)
may rise earlier than other markers
What is an issue with urinalysis?
subjective due to colour being judged by eye
need to check use-by date
time sample collection (morning)
What are the 3 types of proteinuria?
overflow: raised plasma concentration of low MWT proteins, exceeding resoprtive capacity of tubules
glomerular: increased permeability of glomerulus
tubular: decreased resorption
Why is dipstick protein measured as a ratio alongside creatinine?
to account for variation in urine concentration
What is microalbuminura?
Albumin higher than normal in urine due to glomerular proteinuria, but too low to be tested by dipstick
How many stages of AKI are there and how are they decided/diagnosed?
3
increasing serum creatinine
decreasing urine output/anuria
How is CKD diagnosed?
eGFR from CKD-EPI equation
albumin:creatinine ratio
use of cystatin C in patients with mild/moderate renal impairment
