Chapter 2 - Renal Function Tests

Question 1

Broad range of tests that investigate the normal functions performed by the kidney

Together with careful history, physical examination and imaging can contribute to making an accurate diagnosis of specific Kidney disease

Answer 1

Renal Functional Test

Question 2

Clinical Application of Renal Function Tests

Answer 2

1. To asses the functional capacity of kidney
2. Screening & Diagnosis of kidney disease.
3. Follow up the progression of kidney disease
4. Monitor the response to treatment
5. As a routine preoperative investigation.
6. As a routine precaution after starting certain drugs to check if kidney is damaged (as a side-effect).

Question 3

When to assess renal function?

Answer 3

1. Kidney Disorders
2. Vulnerable Groups
3. Systemic disease
4. Drug toxicity
5. Preoperative

Question 4

Tests evaluated in Renal Functional Tests

Answer 4

Glomerular filtration
Tubular reabsorption
Tubular secretion
Renal blood flow

Question 5

is widely accepted as one of best overall measure of kidney function

Answer 5

Glomerular Filtration Rate

Question 6

A decrease in GFR precedes kidney failure in most forms of

Answer 6

progressive renal parenchymal diseases

Question 7

GFR is measured by using the -

Answer 7

clearance of a substance present in plasma that is filtered freely at the glomerulus, but is neither reabsorbed nor secreted by the tubule

Question 8

GFR is useful in:

Answer 8

• In targeting treatment
• Monitoring progression
• Predicting the point at which renal replacement therapy will be required
• Used as a guide to dosage of renally excreted drugs to prevent potential drug toxicity

Question 9

To measure GFR, most methods involve the kidney’s ability to clear (CLEARANCE) either _______________

Answer 9

an exogenous or endogenous marker.

Question 10

Stage 1 GFR Value

Answer 10

> 90 (Normal GFR)

Question 11

Stage 2 GFR Value

Answer 11

60-89 (Mild decreased GFR)

Question 12

Stage 3 GFR Value

Answer 12

30-59 (Moderate decreased GFR)

Question 13

Stage 4 GFR Value

Answer 13

15-29 (Severe decreased GFR)

Question 14

Stage 5 GFR Value

Answer 14

<15 (Renal Failure

Question 15

The volume of plasma from which the substance is completely cleared by the kidneys per unit time.”

Measures the rate at which the kidneys are able to remove or clear a filterable substance from the blood

Answer 15

Concept of Clearance

Question 16

Characteristics of an Ideal Substance for Measuring GFR:

Answer 16

Stable
Inert
Freely Filtered
Neither Secreted Nor Reabsorbed

Question 17

Characteristics (GFR) - : The substance should have a constant concentration in the blood.

Answer 17

Stable

Question 18

Characteristics (GFR) - It should be physiologically inert, meaning it does not affect or alter kidney function.

Answer 18

Inert

Question 19

Characteristics (GFR) - The substance should be able to pass through the glomeruli freely, without any restrictions.

Answer 19

Freely Filtered

Question 20

Characteristics (GFR) - After filtration, the substance should not be reabsorbed back into the bloodstream or secreted by the renal tubules.

Answer 20

Neither Secreted Nor Reabsorbed

Question 21

Markers for Exogenous Markers

Answer 21

Inulin
Iohexol and Iothalamate

Question 22

Endogenous Markers

Answer 22

Creatinine
Cystatin C
Urea

Question 23

considered the gold standard for measuring the glomerular filtration rate (GFR)

very accurate and reliable indicator of kidney function.

not commonly used in routine clinical practice

Answer 23

Inulin Clearance Test

Question 24

is the current routine test substance

Answer 24

Creatinine Clearance

Question 25

Advantages of Creatinine Clearance

Answer 25

Waste product of muscle destruction found at relatively constant plasma level

Automated chemical tests

Question 26

Methods for Creatinine Clearance Test

Answer 26

1. 24 hour urine sample is preferred
2. First voided sample is discarded
3. Subsequently all urine passed is collected in containers
4. Next morning voided sample is collected and all containers are sent to laboratory
5. A blood sample is obtained at midpoint of urine collection
6. Cimetidine which blocks renal secretion can be used to prevent overestimation
7. Final calculation is by the formula UV/P, with adjustment of 10% for secretion

Question 27

Disadvantages of Creatinine Clearance Test

Answer 27

• Small amounts of creatinine secreted by renal tubules can increase even further in advanced renal failure
• Creatinine level is affected by intake of meat and muscle mass
• Collection of urine is incomplete often
• Creatinine levels are affected by drugs such as cimetidine, probenecid and trimethoprim that block tubular secretion

Question 28

Normal values for Creatinine Clearance

Answer 28

Men: 107-139 mL/min
Women: 87-107 mL/min

Question 29

Creatinine is produced as a result of __________; therefore, normal values are based on size; the larger the person, the more creatinine produced

Answer 29

muscle destruction