Thu11November0627PM 6
Renal glomerular function is measured using clearance techniques.
Which one of the following is the most accurate marker for the measurement of glomerular filtration rate?
(Please select 1 option)
Urinary clearance of 125I-iothalamate
Para-aminohippuric acid (PAH)
Creatinine
Plasma clearance of 51chromium EDTA
Inulin Correct
Explanation
The ideal glomerular filtration marker should be:
Non-toxic to the human body
Measured accurately by chemical or physical means
Freely and evenly diffusible throughout the extracellular fluid (ECF) compartment
Unable to enter the intracellular fluid (ICF) compartment, and
Removed from the blood only by filtration in the kidney.
The ideal marker should NOT be reabsorbed into the blood from the renal tubules or other parts of the urinary system.
Creatinine is endogenous and is freely filtered by the glomerulus, but is also secreted by the proximal tubule. Thus, creatinine clearance systematically overestimates GFR. This overestimation is approximately 10% to 40% in normal individuals, but is greater and more unpredictable in patients with chronic kidney disease.
The gold standard method of inulin clearance requires an intravenous infusion and timed urine collections over a period of several hours making it expensive and burdensome. Inulin is in short supply and difficult to mix and maintain as a solution.
Exogenous filtration markers:
Plasma clearance of 51chromium EDTA is a widely used method in Europe but may undergo tubular reabsorption.
Urinary clearance of 125I-iothalamate can be excreted by renal tubules and cannot be used in patients with iodine assay.
These methods have the requirement for storage, administration, and disposal of radioactive substances.
Para-aminohippuric acid (PAH) is freely filtered by the glomerulus and any left in the peritubular capillaries is secreted into the proximal convoluted tubules. This marker is used in the measurement of renal blood flow.
Answer Statistics
1
5%
2
11%
3
11%
4
5%
5
70%
Times answered: 263