Quiz 1: Renal Function

Question 1

Renal Function in Acid/Base Balance

Answer 1

Bicarbonate ions & H+ ions are produced within the tubules as a result of carbonic anhydrase
• H2O + CO2 to H2CO3 to H+ + HCO3-

Question 2

Glomerular filtrate

Answer 2

Glomerular filtrate is a plasma filtrate where glucose and protein are reabsorbed
• filtration influenced by: cellular structure, hydrostatic pressure, under feedback of Aldosterone/Renin system, number of functioning nephrons

Question 3

Creatinine

Answer 3

Skeletal muscle dehydration product which is excreted into circulation at a relatively constant rate proportional to the amount of muscle mass and regulated by kidney function
Increased serum Creatinine indicates Renal Disease/Failure

Question 4

Uric Acid

Answer 4

From breakdown of purines, most is reabsorbed in proximal tubule
Increased in Gout, Renal Failure, Leukemia, and Chemotherapy

Question 5

BUN

Answer 5

Blood Urea Nitrogen
• Greatly affected by renal function and perfusion
• Abnormal levels due to decreased renal blood flow from: CHF, shock, dehydration, hemorrhage
• “Azotemia”: high BUN
• “Uremia”: azotemia with renal failure

Question 6

Clearance Tests

Answer 6

• Measures the rate at which the kidneys remove a substance within a timed interval
• Endogenous vs. Exogenous
Endogenous examples: urea, creatinine, originating or produced within the individual
Exogenous examples: inulin, radioisotopes, para amino hippurate (PAH) test

Question 7

Exogenous Clearance Tests

Answer 7

Originating or produced outside, drugs administered to patients, & methods may cause adverse reactions.
•Insulin: introduced into patient via IV/oral then voided for measurement
• Radioisotopes: Show nuc med renogram
• PAH: para amino hippurate: injected via IV, cleared rapidly by kidneys within half hour. Measured in urine, measurement of renal secretion

Question 8

Creatinine Clearance Test

Answer 8

• Clearance = (U x V) / P : urinary creatinine x total volume divided by Plasma creatinine
OR
Corrected Cr Cl = Cr Cl X 1.73 / BSA
• greatest source of error is in the collection of the ENTIRE specimen
• Correction for ht/wt by using nomograms
• Avoid measurements in early renal and muscle- wasting diseases

Question 9

Clinical Implications of Uric Acid Testing

Answer 9

• Hyperuricemia: Gout, Chemotherapy, Menopause, Renal disease, Lesch-Nyhan syndrome: genetic deficiency of enzyme needed for synthesis of purines
• Hypouricemia: less common, Over treatment of cancer therapy due to liver damage

Question 10

Renal Tubular Reabsorption Tests

Answer 10

• Assessment of renal concentration and dilution ability of renal tubules
Tested by:
1) specific gravity
• refractometer
• urinometer
2) osmolality
• freezing point depression (Value increases in proportion to the increase of solutes regardless of the type- equally influenced by large and small molecules, refers to the number of moles of solute / per kilogram of solvent, one mole of solute / one liter solvent = one osmole)
• vapor depression (volatile solutes can interfere)

Question 11

Isothenuria

Answer 11

Can be detected if specific gravity is measured throughout the day
Hallmark of renal failure - Kidneys lack the ability to concentrate or dilute urine so that the blood filtrate remains unchanged and respond to the body’s hydration status

Question 12

Glomerular Filtration Rate (GFR)

Answer 12

Best overall index of kidney function in health and disease.
Normal GFR varies according to age, sex, and body size; in young adults it is approximately 120-130ml/min/1.73 m2 and declines with age.

Question 13

List Renal Tests

Answer 13

1. BUN
2. Creatinine
3. Uric Acid
4. Creatinine Clearance
5. GFR
6. Osmolality
7. Urinalysis

Question 14

Non-Protein Nitrogens

Answer 14

Urea, Creatinine, Uric Acid, Ammonia

Question 15

Azotemia

Answer 15

Urea, Creatinine, Uric Acid, Ammonia increased in the plasma during renal impairment

Question 16

Creatinine Clearance Equation

Answer 16

[Urine Creatinine/Serum Creatinine] x [Vl 24hr urine/Time elapsed (usually 24hr)]
Expressed in mL/min
Correction for Body Surface Area: Clearance x [1.73/area]

Question 17

Jaffe Reaction

Answer 17

Classic Method of Creatinine Clearance Measurement
Creatinine reacts with picric acid in alkaline sln that is measured spectrophotometrically
Interferents include Glucose, Aceotoacetate, and Ascorbic Acid

Question 18

BUN Measurement

Answer 18

Kinetic Method: Urease hydrolyzes urea into ammonia that can be measured with ISE or spectrophotometrically
Chemical Method: Diacetyl and Urea combine to give a diazine derivative that is yellow in color

Question 19

BUN/Creatinine Ratio

Answer 19

Normally about 10:1 and 20:1

Question 20

Uric Acid measurement

Answer 20

Uric Acid reduces phosphotungstic acid to tungsten blue measured spectrophotometrically

Question 21

Ammonia

Answer 21

Product of deamination of Amino Acids normally metabolized by Liver into Urea
High levels are toxic to CNS, found in Advanced Liver Disease (Reye’s Syndrome, Cirrhosis, Viral Hepatitis) and Impaired Renal function

Question 22

Causes of Falsely Elevate Ammonia Levels

Answer 22

Failure to test in timely manner or place on ice during transport, poor venipuncture, incomplete collection tube filling

Question 23

Urea

Answer 23

Major Nitrogen containing compound in blood from protein catabolism in the Liver then excreted by Kidneys
Abnormal levels may be due to prerenal, renal, or postrenal disorders
Increased: Renal failure, glomerular nephritis, urinary tract obstruction, congestive heart failure, dehydration, increased protein catabolism
Decreased: Severe Liver disease, vomiting/diarrhea

Question 24

Converting BUN to Urea

Answer 24

BUN x 2.14 = Urea

Question 25

Ammonia Measurement

Answer 25

Alpha-ketoglutarate, ammonia, and glutamate dehydrogenase react to form Glutamate and NADP+