Renal Function and Nonprotein Nitrogen

Question 1

What is increased in plasma indicating renal impairment?

Answer 1

All non-protein nitrogens (urea, creatinine, uric acid, and ammonia).

Question 2

Define azotemia.

Answer 2

The increase of non-protein nitrogens in plasma.

Question 3

What is the best laboratory evaluation when suspecting renal impairment?

Answer 3

Glomerular Filtration Rate (GFR).

Question 4

What is used to evaluate the GFR?

Answer 4

Creatinine clearance; more sensitive than BUN or creatinine.

Question 5

What is the calculation used for creatinine clearance?

Answer 5

((U creat)/(P creat)) x ((Volume 24-hr urine)/(1440 (min/24hr)))

Question 6

What test takes the patient’s demographics into consideration for its calculation?

Answer 6

eGFR.

Question 7

Creatinine is synthesized from…

Answer 7

creatine in the muscle.

Question 8

(T/F) Creatinine is used to evaluate renal function and is NOT as sensitive as GFR.

Answer 8

True.

Question 9

What method is used for creatinine testing? Describe this method.

Answer 9

Jaffe reaction; creatinine reacts with picric acid in basic solution, forms a red-orange complex, and read at 490-540 nm.

Question 10

What are some analyte interferences to creatinine testing?

Answer 10

Glucose, acetoacetate, and ascorbic acid.

Question 11

Blood urea nitrogen (BUN) is increased in what condition? How does high-protein diets affect BUN?

Answer 11

Impaired renal function; increases with high protein diets.

Question 12

What are the two testing methods used for BUN measurement?

Answer 12

Colorimetric and enzymatic methods.

Question 13

What enzyme is used in the enzymatic method of BUN measurement?

Answer 13

Urease.

Question 14

Normal BUN/Creatinine ratio.

Answer 14

10:1 - 20:1.

Question 15

Cystatin C is a serum marker for ___.

Answer 15

GFR.

Question 16

What method is used to measure cystatin C?

Answer 16

Immunoassay.

Question 17

Describe A1 Albuminuria.

Answer 17

24-hr urine albumin: <30 mg/24hr (N to mild ↑).

Question 18

Describe A2 Albuminuria.

Answer 18

24-hr urine albumin: 30-300 mg/24hr (moderate ↑).

Question 19

Describe A3 Albuminuria.

Answer 19

24-hr urine albumin: >300 mg/24hr (Severely ↑).

Question 20

Uric acid is the end product of ___ metabolism.

Answer 20

purine.

Question 21

Uric acid is increased in what conditions?

Answer 21

Gout, renal failure, leukemia, and chemotherapy treatments.

Question 22

What testing method is used for uric acid? What analyte interferences may cause altered results?

Answer 22

Colorimetric method; lipids and drugs.

Question 23

What is a by-product of the enzymatic assay of uric acid?

Answer 23

Hydrogen peroxide.

Question 24

Ammonia is synthesized from…

Answer 24

the action of bacteria on the contents of the colon; metabolized by liver normally.

Question 25

Increased ammonia levels is toxic to ___.

Answer 25

CNS.

Question 26

Hyperammonemia is common in what conditions?

Answer 26

Advanced liver disease (most common): Reye’s syndrome, cirrhosis, viral hepatitis

Impaired renal function: elevated BUN.

Question 27

What pre-analytical errors may cause a false increase in ammonia?

Answer 27

Failure to place sample on ice/not test immediately; poor venipuncture technique.