Renal Function and Automation

Question 1

Osmolality determinations are preferred, over S.G., for the evaluation of ___.

Answer 1

Renal concentrating ability.

Question 2

Why is osmolality more accurate?

Answer 2

Because each solute particle contributes equally to the osmolality value.

Question 3

How is osmolality tested?

Answer 3

Freezing point depression and vapor pressure osmometers.

Question 4

What are the three most prevalent urine solutes?

Answer 4

Urea, sodium, and chloride.

Question 5

When ADH production or secretion is defective, this indicates what?

Answer 5

Neurogenic diabetes insipidus.

Question 6

What condition occurs when there is a lack of renal response to ADH?

Answer 6

Nephrogenic diabetes insipidus.

Question 7

A fluid deprivation test evaluates what?

Answer 7

The ability of renal tubular cells to selectively absorb and secrete solutes. In other words, it assesses the renal concentrating ability of the kidneys.

Question 8

During a fluid deprivation test, if the urine osmolality is greater than 800 mOsm/kg, what does this indicate?

Answer 8

A normal result.

Question 9

What occurs if a fluid deprivation test is failed?

Answer 9

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.

Question 10

What is indicative of a negative response to ADH?

Answer 10

Nephrogenic problem - the renal receptors for ADH are dysfunctional.

Question 11

How would you calculate osmolar clearance?

Answer 11

The ratio of urine osmolality to serum osmolality multiplied by the timed urine volume.

=Uosm (mOsm/kg)/Sosm (mOsm/kg) X Vol (mL/min)

Question 12

The total volume of urine excreted by the kidneys actually consists of what two separate volumes?

Answer 12

Osmolar clearance water and solute-free water.

Question 13

What is the osmolar clearance water?

Answer 13

The volume of water required to eliminate the solutes from the plasma.

Question 14

What is the solute-free water?

Answer 14

Additional water that exceeds bodily needs, is retained in the tubules, and is eliminated in the urine.

Question 15

A negative free-water clearance is indicative of what?

Answer 15

The kidneys are reabsorbing water and are producing urine that is hyperosmotic or hypertonic.

Question 16

For the kidneys to remove metabolic wastes and selectively reabsorb solutes and water, they require adequate ___ through the glomeruli.

Answer 16

renal plasma flow.

Question 17

The renal plasma flow (RPF) determines what?

Answer 17

The amount of plasma ultrafiltrate processed by the nephrons to the kidneys.

Question 18

Define renal clearance.

Answer 18

The volume of plasma in milliliters that is completely cleared of a substance per unit of time.

Question 19

How do you calculate renal clearance?

Answer 19

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.

Question 20

Substances that are removed exclusively by glomerular filtration (e.g., insulin) can be used to determine what?

Answer 20

Glomerular filtration rate (GFR).

Question 21

Any substances that (1) ___, (2) ___, and (3) ___, can be used to determine GFR.

Answer 21

(1) Maintains constant plasma level.
(2) Excreted solely by glomerular filtration.
(3) Is not reabsorbed or secreted by the tubules.

Question 22

What is the reference method for GFR determination?

Answer 22

Inulin Clearance.

Question 23

Why is creatinine used, over urea, for clearance testing?

Answer 23

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.

Question 24

How is creatinine formed?

Answer 24

As a byproduct of muscle metabolism; formed from creatine and phosphocreatine.

Question 25

Why does the creatinine clearance test dependent on the gender of the patient?

Answer 25

Creatinine production depends directly on muscle mass; males and athletes produce more creatinine compared to women, children, and the elderly.

Question 26

Because of dependence on individual muscle mass, creatinine clearance values are normalized to the external body surface area of an average individual by a factor of ___.

Answer 26

1.73 m^2

Question 27

What is the equation for normalized creatinine clearance?

Answer 27

C (mL/min) = (UxV/P) x (1.73/SA)

C=creatinine clearance; U=urine concentration of creatinine; V=volume of urine excreted in mL/min; P=plasma concentration of creatinine; SA=patient’s body surface area.

Question 28

How does lipemic specimens effect the osmolality?

Answer 28

False increase.

Question 29

How does lactic acid effect osmolality?

Answer 29

False increase.

Question 30

What is the ideal ratio of urine to serum osmolality after controlled fluid intake?

Answer 30

3:1.

Question 31

Following an ADH injection, a patient DOES NOT have a urine:serum osmolality of 3:1. What does this indicate?

Answer 31

Lack of ADH receptors.

Question 32

Following an ADH injection, a patient has a urine:serum osmolality of 3:1. What does this indicate?

Answer 32

Lack of ADH production.

Question 33

What is the function of ADH?

Answer 33

Reabsorbs water from the tubules.

Question 34

What is the specimen of choice for GFR testing?

Answer 34

24-hour urine collection.

Question 35

What are some factors