Assessment of renal function Flashcards
Define these: ESRF CKD ARF HD/HF CAPD AKI eGFR
End Stage Renal Failure Chronic Kidney Disease Acute Renal Failure Haemodialysis/haemofiltration Continous Ambulatory Peritoneal Dialysis Acute Kidney Injury Estimated Glomerular Filtration Rate
What hormones are released in the kidney?
Erythropoietin (blood oxygen), renin (plasma sodium levels), prostaglandins, 1a-vitD3 hydroxylation
What are some common symptoms of kidney disease? and why do they go unnoticed?
hypertension, urinary frequency or volume (normal people dont track this). All very non specific
Late stage often include; fatigue, nausea, vomiting, poor appetite, shortness of breath, fluid retention.
What are the main laboratory investigations used to test for kidney disease?
Imaging, histology and microscopy, immunology, biochemistry (urinalysis and other biomarkers)
What are some disadvantages to using imaging to investigate kidney condition?
expensive and the full damage cannot be assess + its extent
The functionality is not tested
BUT can detect masses e.g. cancer
What advantages does imaging have in assessing kidneys?
Looking at the size, symmetry and obstruction. You can also get a larger view of the connected organs and tissue - bladder, ureter and prostate glands
Name some immunology tests and what disease they investigate?
complement: low C4- systemic lupus erythematosus and cryoglobulinaemia
anti-glomerular basement membrane antibodies: goodpastures disease
cANCA: associated with vasculitis - wegeners disease
pANCA: associated with vasculitis
In what situation is a immunological approach to kidney assessment appropriate?
for specific diseases
What is a quick bedside snapshot of the kidney state/functionality?
urine dipstick - gives the operator a quick snapshot of what is going on and its non invasive, however it is not very specific.
Operator error, inter-operative variability, requires fresh urine
What are some quantitative markers of glomerular filtration?
creatinine, urea, proteinuria
What are some quantitative markers of tubular function? and what do they test?
pH (H+) (acid-base balance), urine volume/osmolality, phosphate, aminoaciduria, glycosuria, beta2-microglobulin
assessment of renal ability to ajust Na, K, H ions, water compoistion of filtrate & reabsorb small proteins, amino acids and glucose
What disease is associated with the improper absorption of phosphate, glucose and amino acids?
Fanconi syndrome
5 characteristics of ideal markers of kidney function.
Its freely filtered at the glomerulus
Not reabsorbed in the tubules
Its not secreted from the blood stream into the filtrate
Not metabolised and/or broken down in the kidney
It is not synthesised at any point in the kidney
Name the gold standard to assessing glomerular filtration, using an exogenous marker.
Inulin: metabolically inert sugar, provides good GFR
Disadvantages
Intravenously, expensive
How does an exogenous marker work and what do they test?
Introduced intravenously and provides a good GFR estimation using a urinalysis.
- measure how much is released over a time period (ml/min)
The marker should be freely filtered and metabolically inert
What are some common endogenous markers to assess glomerular filtration?
Urea: end product of nitrogenous metabolism
Creatinine: product of muscle metabolism, fairly constant rate of production
Cystatin C: small protein produced by all nucleated cells
Neutrophil Gelatinase Associated Lipocalin (NGAL): newer marker of AKI
Why can urea produce unreliable results?
It can give a false positive almost, where the levels do not match with the state of the person.
Urea levels can be skewed in people with high protein diets (high urea), GI bleeds (high urea), extremes of hydration states or low in liver disease. It is also passively reabsorbed in the renal tubules
Creatinine levels excreted can give false snapshots. True or false
True. The creatinine levels excreted will differ from person to person and is dependent on muscle mass, age, sex and ethnicity.
Therefore, creatinine can be confusing in the extremes - such as body builders or old elderly people
also affected by gender and race
Furthermore, the GFR has to fall by a substantial amount before the creatinine rises
What advantages does cystatin C have over urea and creatinine as a endogenous marker?
It is not affected by muscle mass, age, gender or race
In relation to serum creatinine how does a lowered GFR affect it?
The plasma/serum creatinine increases as there is a reduced creatinine clearance -
Creatinine clearance decreases
How is urine collected for a urinanalysis?
Day 1: 8am empty bladder
Commence 24h urine collection - All urine now passed until 8am next day must be collected into container
Day 2: 8am collect final urine output into container
Hand in urine sample with a blood sample
What variables are used in producing a eGFR?
Serum creatinine, age, sex, ethnicity
protein excretion should be >0.15g/24h. True or false
False, it should be <0.15g/24h.
Protein loss of >3g/24h result in nephrotic syndrome
Define ACR and PCR.
Protein:Creatinine ratio
Albumin:creatinine ratio
Microalbumin describes what? And what test is suitable to detect it?
The ability to detect albumin at low levels in urine
Dipstick is not sensitive enough so urinalysis is needed.
What can cause urine to go cloudy?
Urinary sediment, such as RBC, hyaline and casts.
RBC casts imply haemoglobinuria (poor filtering - larger compounds able to pass), due to glomerular disease
Why does proteinuria occur?
Increase in filtered load (globular permeability increase) or decrease in reabsorptive capacity (due to tubular damage)
Describe glomerular proteinuria.
Increased permeability allows larger proteins to be excreted such as albumin
Describe tubular proteinuria.
There is a decreased reabsorption of freely filtered small proteins resulting in higher concentrations released in the urine.
Likely to cause K, Na, and bicarbonate to be increased in urine
Assumptions of ACR and PCR
Normal urine output and creatinine excretion.
Binary gender - not transgender
What electrolytes can be used to determine tubular function? (serum)
K- often high due to low GFR= inability of excretion. Can be low in some conditions
Na – can be low/high/normal. Often useful to assess fluid status
Ca – often low due to defective 1alpha hydroxylation of vitamin D which takes place in the kidney
PO4 and Mg – often high due to low GFR=inability of excretion (however are sometimes low due to increased renal losses especially post-Tx)
Potassium, phosphate and Mg is often high due to a low GFR. True or False
True. The low GFR means there is an inability of excretion
What does the sodium levels in urine tell you?
Fluid status. Often Na in urine is compared to plasma sodium
Low Ca in urine may be due to what defective biochemical reaction? and where does this reaction take place?
A defective 1alpha hydroxylation of vitamin D which takes place in the kidney.
Active vitamin D deficiency can also cause low Ca
What is CKD? and what differs it from AKI?
Abnormal function or structure that has persisted for 3 months, with implications for health.
Includes people with markers of kidney damage and GFR <60ml/min/1.73m on 2 occasions seperated by 90 days
What are the NICE CKD assessment recommendations? and what test may you use?
eGFRcreatinine
Do not eat meat within 12h, because it will increase creatinine in your blood.
Interpret results with caution to muscle mass. reduced muscle mass results in overstimulation and increased muscle mass leads to underestimation of GFR.
eGFRcystatin C
Used at inital diagnois or rule out CDK.
When is an eGFRcystatin C useful?
When eGFRcreatinine of 45-59 is sustained for 90 days with no proteinuria (less than 3mg/mmol - ACR)
Define AKI
Acute kidney injury - has existed for less than 3 months.
Comparing current creatinine to a reference/baseline to see how much it has increased.
stage 1 - increase of >26umol/L within 48h
stage 2- increase>2 to 2.9 x reference
stage 3- increase >354umol/L or 3x reference
By what measurements is AKI assessed?
urine output and serum creatinine
Do both measurements need to be meet to conclude AKI?
No, one is substantial enough
NICE AKI recommendations
Monitor the development or progression of CKD for 2-3 years post AKI even if creatinine is normal
Is the creatinine level enough to justify a diagnosis of AKI?
A. Yes
B. It can be with decreasing urea
C. It should not be used due to the variables due to age, sex, gender and ethnicity
D. If there is a simultaneous increase in urea
D
How can the stage of AKI be determined using a range of results?
A. The stage can be assumed freely based on the reference limits
B. Divide the current measure of creatinine by the baseline of the patient
C. Divide the measure of serum creatinine by measure of urine urea
D. Divide the creatinine level by the upper reference limit
B
A patient is presenting with high levels of serum creatinine, and has no past evidence of high levels of creatinine. What does the patient have?
A. On HD
B. ESRF
C. CKD
D. AKI
D
Test results from a patient come in showing abnomally raised levels of creatinine and urea. What do you diagnose the patient with?
A. Nothing, but request another test be done in 24H
B. AKI
C. Dehydration
D. CKD
A
Using past lab tests what is the time span for chronic abnormal creatinine levels to be labelled as a CKD?
A. 1 month
B. 3 months
C. 10 months
D. 1 year
B
A patient’s blood work and urinalysis are received. The patient shows two varying creatinine levels on the same day. This has occurred in the past 2 months. What can you tell about the patient?
A. Prostate cancer
B. Needs further monitoring to conclude
C. Imbalance of water intake
D. On haemodyalisis
D
How can overhydration skew blood and urinalysis?
A. low eGFR, serum creatinine high
B. high eGFR, serum creatinine low
C. low eGFR, serum creatinine low
D. high eGFR, serum creatinine high
A
Name as many analytes in urinalysis.
Glucose, amino acids, pH, bilirubin, uribilinogen, protein, nitrite, blood, ketones
Why might ketones be detected in the urine? and what disease does it occur in?
Fat is being used as an energy source rather than storage.
- Can be seen in diabetic and alcoholic ketoacidosis
Identify as many freely filtered proteins (normally reabsorbed) and their use as a biochemical marker.
A. Albumin B. Beta-2-microglobulin C. Gamma-1-microglobulin D. Omega-2-microglobulin E. Alpha-1-microglobulin
B and E - indicate whether there is a tubular dysfunction present where the tubular sections are unable to freely reabsorb small proteins
What are some consequences of chronic renal failure?
- Reduced vitamin D activation causing oversecretion of PTH by thyroid - can lead to hyperparathyroidism and hypercalcemia
- Retention of H+ causing metabolic acidosis
What are some interferences to the dipstick test?
Blood analysis - menstruation (+), vit C (-)
Protein analysis - infected urine (+), dilute urine (-)
At what GFR does the creatinine begin to fall? and why could this be a problem?
> 50ml/min - problem because this is quite far below the natural range of 90-120
When should eGFR not be used?
- AKI
- Children
- Pregnancy
- Amputees
- Muscle wasting disease
- Malnourished
Match the following electrolytes with correct statments:
A. K B. Ca C. Na D. Mg E. PO4
- Low due to defective alpha-1 hydroxylase of Vit D
- Often low in decreased GFR due to inability to excrete
- Useful to determine fluid status
- All of the above are applicable
- None suit this
A2 B1 C3 D2 E2
How does muscle mass affect the creatinine estimation?
Reduced muscle mass will overestimate creatinine levels.
What should the reference value for creatinine in AKI consideration be used?
The lowest creatinine level collected within 3 months of the event
