Renal Function and Automation Flashcards
Osmolality determinations are preferred, over S.G., for the evaluation of ___.
Renal concentrating ability.
Why is osmolality more accurate?
Because each solute particle contributes equally to the osmolality value.
How is osmolality tested?
Freezing point depression and vapor pressure osmometers.
What are the three most prevalent urine solutes?
Urea, sodium, and chloride.
When ADH production or secretion is defective, this indicates what?
Neurogenic diabetes insipidus.
What condition occurs when there is a lack of renal response to ADH?
Nephrogenic diabetes insipidus.
A fluid deprivation test evaluates what?
The ability of renal tubular cells to selectively absorb and secrete solutes. In other words, it assesses the renal concentrating ability of the kidneys.
During a fluid deprivation test, if the urine osmolality is greater than 800 mOsm/kg, what does this indicate?
A normal result.
What occurs if a fluid deprivation test is failed?
A patient is administered with ADH (vasopressin) and tested again a few hours later to determine:
(1) Urine osmolality is >800 mOsm/kg
(2) Urine osmolality to serum osmolality (U/S) is greater than 3.0.
What is indicative of a negative response to ADH?
Nephrogenic problem - the renal receptors for ADH are dysfunctional.
How would you calculate osmolar clearance?
The ratio of urine osmolality to serum osmolality multiplied by the timed urine volume.
=Uosm (mOsm/kg)/Sosm (mOsm/kg) X Vol (mL/min)
The total volume of urine excreted by the kidneys actually consists of what two separate volumes?
Osmolar clearance water and solute-free water.
What is the osmolar clearance water?
The volume of water required to eliminate the solutes from the plasma.
What is the solute-free water?
Additional water that exceeds bodily needs, is retained in the tubules, and is eliminated in the urine.
A negative free-water clearance is indicative of what?
The kidneys are reabsorbing water and are producing urine that is hyperosmotic or hypertonic.
For the kidneys to remove metabolic wastes and selectively reabsorb solutes and water, they require adequate ___ through the glomeruli.
renal plasma flow.
The renal plasma flow (RPF) determines what?
The amount of plasma ultrafiltrate processed by the nephrons to the kidneys.
Define renal clearance.
The volume of plasma in milliliters that is completely cleared of a substance per unit of time.
How do you calculate renal clearance?
C (mL/min) = U (mg/dL) x V (mL/min) / P (mg/dL)
C= renal clearance; U= urine concentration; P= plasma concentration; V=timed collection volume.
Substances that are removed exclusively by glomerular filtration (e.g., insulin) can be used to determine what?
Glomerular filtration rate (GFR).
Any substances that (1) ___, (2) ___, and (3) ___, can be used to determine GFR.
(1) Maintains constant plasma level.
(2) Excreted solely by glomerular filtration.
(3) Is not reabsorbed or secreted by the tubules.
What is the reference method for GFR determination?
Inulin Clearance.
Why is creatinine used, over urea, for clearance testing?
Creatinine is not reabsorbed by the renal tubules. Nor is it affected by the urine flow rate, and plasma levels are not altered by a normal diet.
How is creatinine formed?
As a byproduct of muscle metabolism; formed from creatine and phosphocreatine.
