Vanders Renal Ch3 Flashcards
Define the term clearance in a biomedical context
The volume of plasma per unit time from which all of a specific substance is removed
What is metabolic clearance rate?
The quantitative measure of how a substance is removed from the plasma by any of the body’s mechanisms
Differentiate between general clearance and specific renal clearance
General clearance refers to removal by any means, while renal clearance is specifically by the kidneys
What information is required to calculate clearance?
Plasma concentration of the substance, urine concentration, and urine flow rate
What criteria must a substance meet to be used as a measure of glomerular filtration rate (GFR)?
The substance must be freely filtered, not reabsorbed or secreted
Which substances are commonly used to measure GFR?
Inulin and creatinine
What is the significance of inulin clearance?
It specifically indicates renal clearance and is used to measure GFR
Calculate the clearance of a substance given its excretion rate and plasma concentration
Clearance (Cx) = Excretion rate (Ux * V) / Plasma concentration (Px)
What does a clearance greater than GFR indicate?
Net secretion of the substance
What does a clearance less than GFR indicate?
Net reabsorption of the substance
What is the gold standard for measuring GFR?
Inulin clearance
What is the common method to measure GFR in patients?
Creatinine clearance
Why does creatinine clearance slightly overestimate GFR?
A small amount of creatinine is secreted by the proximal tubule
What is the relationship between plasma creatinine concentration and GFR?
They vary inversely; as GFR decreases, plasma creatinine increases
Fill in the blank: Plasma concentration of _______ is a practical indicator of GFR.
creatinine
True or False: All substances used to measure GFR must be reabsorbed by the kidneys.
False
What is the role of cystatin C in estimating GFR?
Cystatin C is produced at a constant rate and is cleared by glomerular filtration, reflecting GFR
What is the typical plasma concentration of creatinine in a healthy person?
About 1 mg/dL
What happens to plasma creatinine concentration if GFR decreases by 50%?
Plasma creatinine stabilizes at 2 mg/dL
What is the significance of the clearance units?
They are expressed as volume per time, reflecting the volume of plasma cleared of a substance
Describe the renal handling of inulin
Inulin is freely filtered, not reabsorbed or secreted, and all filtered inulin appears in the urine
What does the clearance of para-aminohippurate (PAH) indicate?
It indicates effective renal plasma flow, as PAH is filtered and secreted
What does a clearance equal to GFR indicate?
No net reabsorption or secretion has occurred
What are some exogenous agents used to measure GFR?
125I-iothalamate, 59Cr-EDTA, 99mTc-DTPA
What is the advantage of using cystatin C over creatinine for GFR estimation?
Cystatin C is less affected by muscle mass and is cleared more completely
What does clearance express in the context of renal function?
The rate at which a substance is removed from the plasma and excreted in the urine
What is the best measure of GFR?
Inulin clearance
Which clearance can be used as an estimate of renal blood flow?
Para-aminohippurate clearance
What is a practical measure of GFR?
Creatinine clearance
Which two substances are clinically used as indicators of GFR?
- Plasma creatinine concentration
- Cystatin C
What is renal scintigraphy used for?
Assessing the function of each kidney separately
Fill in the blank: Renal clearance of any substance is calculated by a _______.
clearance formula relating urine flow to urine and plasma concentrations
What happens to plasma creatinine levels when GFR is reduced?
Plasma creatinine stabilizes at a higher concentration
True or False: Cystatin C levels are less affected by age, sex, race, and muscle mass than creatinine levels.
True
What is the significance of an increasing plasma creatinine over time?
It is a red flag that there may be a renal problem
What is the effect of large amounts of red meat on creatinine levels?
It may cause a transient increase in creatinine levels
What can MAG3 clearance indicate about kidney function?
Deficient clearance indicates poor ability to clear creatinine and other organic waste
What does a renogram plot represent?
Graphical plot of radioactive counts versus time
What is the typical peak time for healthy kidneys in renal scintigraphy?
3 to 4 minutes
What is the expected plasma urea concentration after 80% nephron destruction if initial concentration was 5 mmol/L?
25 mmol/L
What is the relationship between MAG3 clearance and creatinine clearance?
MAG3 clearance is highly correlated with creatinine clearance
Fill in the blank: Cystatin C measurements have not been shown to be superior to _______.
formula-adjusted estimations of kidney function based on creatinine measurements
What factors are included in eGFR equations?
- Age
- Body size
- Gender
- Race
True or False: Urea measurement is a more accurate indicator of GFR than plasma creatinine or cystatin C.
False
What does the clearance formula relate to?
Urine flow to urine and plasma concentrations
What does a slower rise in kidney counts during renal scintigraphy indicate?
Poor kidney performance
What substance is cleared by the kidneys almost exclusively by secretion?
MAG3
