L 31 Lab test of CKD Flashcards
What are the 3 primary mechanisms of urine excretion
- glomerular filtration
- tubular reabsorption
- tubular secretion
Is tubular transport active or passive?
Both, active and passive
Tubular secretion what is it?
An additional excretory mechanism
Both active and passive
The RAAS system affects ….
Na+ and K+ measurements
Loop of henle reabsorbs:
H2O and Na+
Distal tubule reabsorbs
Na+, K+, H+, HCO3
Proximal tubule reabsorbs
H2O, electrolytes, glucose
What pH is controlled by?
By 2 things i)Lungs ii)Kidneys
What 2 systems regulate pH?
The respiratory and renal systems
What does the kidney do to regulate pH?
Kidney provides a buffering system to help regulate pH
pH is determined by the ratio of _____ and _______.
pH is determined by the ratio of [HCO₃⁻] and PaC02.
The kidneys regulate the concentration of Bicarbonate in the ?
In the plasma
The kidney exchanges … for ….
Exchanges H+ ions (out) for HCO3 (in)
… and … are exchanged intracellularly and extracellularly to maintain a pH balance?
Potassium and Hydrogen are exchanged intracellularly and extracellularly to maintain a pH balance
K+ and H+
How do we estimate renal function? x2
Creatinine clearance and eGFR
What is creatinine?
A chemical compound formed by muscle
Summary of creatinine?
Filtered by glomerulus, not reabsorbed by tubules.
Half life ~6 hours
Creatinine clearance (CLcr) gives us an estimate of?
Gives us an estimate of GFR.
Is serum creatinine a good biomarker?
Not by itself, it is influenced by factors affecting production and elimination
What equation is used to estimate CLcr?
Cockcroft and gault equation
What is the definition of steady state?
Rate of elimination =rate of production
Creatinine production depends or influenced by?
Weight, age and Sex
What are the Limitations to creatinine-based GFR estimators?
- They overestimate GFR in elderly, obese (if use TBW), severe or end stage renal disease
- Not for <18s
- Not for malnourished or low body mass
- Unreliable when renal function changes rapidly (Acute renal failure)
If a patient has a eGFR of 55mL/min/1.73m^2, but their BSA is actually 1.50m^2, what should their eGFR be?
55/1.73 = 31.79
31.79 x 47mL/min
Other issues with creatinine based renal estimations?
- Only useful in steady state condition (not good if renal function is changing)
- Note variability in natural creatine production and drugs that raise creatinine concentration.
These drugs inhibit tubular secretion and therefore raise creatinine concentration x3?
Probenecid, trimethoprim, spironolactone
Creatinine based eGFR equations, CKD-EPI and MDRD only be used in patients with a body-surface area (BSA) of 1.73m^2?
No, you can adjust it if you know the BSA so that it will be accurate.
What is urea? How is it excreted? How is it filtered?
Urea is the end product of protein metabolism.
It is excreted renally
It is filtered by glomerular filtration.
How much urea is reabsorbed in tubules?
50%
If you remove a kidney what happens to eGFR?
Reduce EGFR but not a half will remain the same but reduce a little.
Why is urea not an ideal marker for renal function?
Many non-renal conditions can affect urea
How much filtered urea is reabsorbed in the tubules? When will this increase?
About 50% of urea is reabsorbed in the tubules
This increases during dehydration to increase water reabsorption.
Where is potassium usually found in the body? What is the usual serum concentration?
What is the major role of K+ in the body?
Usually found in intracellular fluid.
Usual serum concentration = 3.5-5.2mmol/L
K+ plays a major role in muscle and nerve function.
Potassium homeostasis is maintained by these 2 primary mechanisms.?
- Shifting potassium in and out of cells
2. Renal elimination
Renal elimination controlled by ?
Aldosterone
Eliminated by distal tubular secretion
How is renal elimination of K+ controlled? What are the 2 options to maintain homeostasis of K+?
K+ renal elimination is controlled by aldosterone.
To increase K+, the body freely filters and the completely reabsorbs K+
To decrease K+, the body eliminates it through distal tubule secretion
Why K+ accumulation occur for CKD patients?
In CKD, K+ secretion is reduced thus it start accumulation of K+
In which stage K+ remain normal of CKD?
In which stage K+ remain normal of CKD?
in stage 3 of CKD
What is the compensatory response to elevated K+? What does this do?
Aldosterone is released which causes an increase in K+ elimination
NOTE: hyperkalaemia can be exacerbated by …..
ACEI, ARBs, K-sparing diuretics
Because they stop the natural aldosterone K+ elimination.
Hyperkalaemia is most common in which stages of CKD?
In which stages do K+ levels often remain normal?
Hyperkalaemia: CKD4 or CKD5
Normal K+ levels: CKD1-3
Where is sodium usually found in the body?
What is the usual serum concentration?
What is the major role of Na+ in the body?
Mainly found in ECF
Usual serum conc = 135-145mmol/L
Major role = to maintain serum osmolality and water balance
Where are sodium and water primarily reabsorbed?
Where are the major sites for regulatory control?
By the proximal tubule
Regulatory control sites are the distal tubule and collecting ducts
Sodium homeostasis is controlled by…
Aldosterone and ADH
How much of the filtered Na+ is excreted in normal renal function?
Normally, 1-3% of filtered Na+ is excreted
As CKD progresses … excretion becomes impaired causing?
As CKD progresses, Na+ excretion becomes impaired causing fluid retention, volume expansion, increased BP, oedema
In late CKD, it becomes a ….problem with CVD?
In late CKD, it becomes a cyclical problem with CVD
As CKD progresses, there are high levels of … and … and … in the body?
Na+ and K+ and H+
Arterial pH is at ?and how it governs by the balance between …. and ….
Arterial pH is normally maintained at 7.36-7.44 by governing the balance between HCO3 and CO2
Overall, metabolic processes produce an excess of … which therefore must be ….
Overall, metabolic processes produce an excess of acid which therefore must be buffered
In CKD there is impaired pH control meaning that … excretion is reduced, but … reabsorption is relatively maintained.What is the result of this?
In CKD there is impaired pH control meaning that H+ excretion is reduced, but HCO3 reabsorption is relatively maintained.
Result = tendency of acidosis
Signs of acidosis
pH <7.35
Acidosis contributes to (x4)
Bone resorption
Muscle wasting
Hyperparathyroidism
Increased CKD progression and mortality
Which patients are at risk with a triple whammy?
Elderly, heart failure patients
What is proteinuria?
Leakage of excess albumin/proteins into the urine.
Where is a protein normally filtered and reabsorbed?
Protein is normally filtered in the glomerulus and reabsorbed by the proximal tubules.
What measures can we use to determine proteinuria?
Spot urine checks and albumin: creatinine ratio (ACR)
Microalbuminuria values?
30-300mg/24hrs
Macroalbuminuria values?
> 300mg/24hrs
Microalbuminuria values using ACR?
2.5-25mg/mmol for men, 3.5-35mg/mmol for women
Macroalbuminuria values using ACR
>25mg/mmol for men, >35mg/mmol for women
What other situations can albuminuria occur in?
After exercise, fever, UTIs
Which one of the following lab results would you expect to INCREASE when initiating an ACEI in a CKD patient?
- eGFR
- Potassium
- pH
- Bicarbonate
Answer: 2. Potassium.
Because aldosterone naturally causes K+ elimination, but blocking the aldosterone pathway will inhibit secretion = increased serum potassium levels
