NPN UREA

Question 1

NPN present in highest concentration in blood?

Answer 1

Urea

Question 2

Where is urea formed and from what substances?

Answer 2

Liver from CO2 and ammonia

Question 3

Major excretory product of protein metabolism?

Answer 3

Urea

Question 4

How is urea concentration expressed?

Answer 4

In terms of nitrogen content (BUN)

Question 5

Conversion factor for BUN to urea?

Answer 5

BUN x 2.14 = Urea

Question 6

Reference method for measuring urea?

Answer 6

Isotope Dilution Mass Spectrometry (IDMS)

Question 7

Reagent used in Fearon method for BUN measurement

Answer 7

Diacetyl monoxime

Question 8

Product formed in Fearon method for BUN measurement

Answer 8

Diazine

Question 9

Color observed in Fearon method for BUN measurement

Answer 9

Yellow

Question 10

Reagent used in Nesslerization method for BUN measurement

Answer 10

K2(HgI4)

Question 11

Color observed in Nesslerization method for BUN measurement

Answer 11

Yellow

Question 12

Reagent used in Berthelot method for BUN measurement

Answer 12

Sodium hypochlorite (NaOCl) and phenol

Question 13

Color observed in Berthelot method for BUN measurement

Answer 13

Blue

Question 14

Enzyme used in enzymatic BUN measurement

Answer 14

Urease

Question 15

Product formed in enzymatic BUN method

Answer 15

2 NH4+ + CO3²-

Question 16

Enzyme used in GLDH-coupled enzymatic method for BUN measurement

Answer 16

Glutamate dehydrogenase (GLDH)

Question 17

Product formed in GLDH-coupled enzymatic method for BUN measurement

Answer 17

Glutamate and NAD

Question 18

Method used for measuring BUN by conductivity

Answer 18

Conductimetric method

Question 19

Reference range for BUN

Answer 19

6–20 mg/dL

Question 20

Condition associated with high BUN in prerenal azotemia

Answer 20

Dehydration, ↓ blood volume

Question 21

Condition associated with high BUN in renal azotemia

Answer 21

Glomerulonephritis, renal failure

Question 22

Condition associated with high BUN in postrenal azotemia

Answer 22

Urinary tract obstruction

Question 23

Condition associated with very high plasma urea concentration and renal failure

Answer 23

Uremia/Uremic syndrome

Question 24

Conditions that can cause low BUN

Answer 24

Repeated dialysis, liver disease, low protein diet

Question 25

Normal BUN/Creatinine ratio

Answer 25

10-20 BUN : 1 creatinine

Question 26

Most common cause of prerenal azotemia

Answer 26

Dehydration

Question 27

BUN/Creatinine ratio indicating prerenal azotemia

Answer 27

> 20:1

Question 28

Other causes of prerenal azotemia

Answer 28

Decreased blood volume, high-protein diet, increased protein catabolism

Question 29

BUN/Creatinine ratio in renal azotemia

Answer 29

~20:1

Question 30

Cause of renal azotemia

Answer 30

Decreased excretion (glomerulonephritis, renal failure)

Question 31

BUN/Creatinine ratio in postrenal azotemia

Answer 31

~20:1

Question 32

Causes of postrenal azotemia

Answer 32

Urinary tract obstruction, nephrolithiasis, tumors, severe infections

Question 33

Condition with very high plasma urea in renal failure

Answer 33

Uremia/Uremic syndrome

Question 34

BUN/Creatinine ratio indicating low BUN

Answer 34

< 10:1

Question 35

Causes of low BUN

Answer 35

Repeated dialysis, liver disease, low-protein diet

Question 36

Substances creatinine is derived from

Answer 36

Methionine, glycine, arginine

Question 37

Factor affecting creatinine excretion rate

Answer 37

Muscle mass

Question 38

How is creatinine eliminated from circulation?

Answer 38

By glomerular filtration

Question 39

Relationship between creatinine concentration and GFR

Answer 39

Inversely related

Question 40

Characteristics of the Jaffe reaction

Answer 40

Colorimetric, endpoint, nonspecific; interference from ascorbic acid, glucose, uric acid

Question 41

Product of the Jaffe reaction

Answer 41

Red-orange tautomer

Question 42

Methods to improve specificity of the Jaffe reaction

Answer 42

Kinetic method, adsorbents (Lloyd's RGT, Fuller's earth)

Question 43

Enzyme used in enzymatic creatinine methods

Answer 43

Creatininase

Question 44

Reaction catalyzed by creatininase

Answer 44

Creatinine + H2O → Creatine

Question 45

Final chromogen reaction in POD-coupled method

Answer 45

H2O2 + chromogen → Oxidized chromogen + H2O

Question 46

Reaction catalyzed by CK in creatininase-CK method

Answer 46

Creatine + ATP → Creatine phosphate + ADP

Question 47

Role of LDH in CK-coupled method

Answer 47

Converts pyruvate + NADH → lactate + NAD+

Question 48

Absorbance change indicating low creatinine in CK-coupled methods

Answer 48

Low absorbance from NAD+ formation

Question 49

Effect of high NADH on absorbance in CK-coupled methods

Answer 49

High NADH causes high absorbance

Question 50

Formula for Creatinine Clearance

Answer 50

Creatinine clearance = (UV/P) × 1.73/A (A = body surface area in m²)

Question 51

MDRD formula for eGFR (mL/min/1.73m²)

Answer 51

eGFR = 170 × Cr^-0.999 × Age^-0.176 × 1.180 (if Black) × 0.762 (if female) × BUN^-0.170 × Alb^-0.318

Question 52

Alternative MDRD formula for eGFR

Answer 52

eGFR = 186 × Cr^-1.154 × Age^-0.203 × 1.212 (if Black) × 0.742 (if female)

Question 53

Difference between old and new MDRD formulas

Answer 53

Old MDRD: 6 variables; New MDRD: 4 variables

Question 54

CKD-EPI formula for eGFR

Answer 54

eGFR = 141 × min(SCr/k,1)^a × max(SCr/k,1)^-1.209 × 0.993^Age × 1.018 (if female) × 1.159 (if Black)

Question 55

Reference value for Serum Creatinine (Jaffe method)

Answer 55

0.9–1.3 mg/dL (M); 0.6–1.1 mg/dL (F)

Question 56

Reference value for Serum Creatinine (enzymatic method)

Answer 56

0.6–1.1 mg/dL (M); 0.5–0.8 mg/dL (F)

Question 57

Reference value for Creatinine Clearance

Answer 57

M = 85-125 mL/min; F = 75-115 mL/min

Question 58

Clinical significance of decreased creatinine clearance or eGFR

Answer 58

Indicates impaired renal function

Question 59

Stages of CKD based on GFR

Answer 59

Stage 1: GFR ≥ 90, Stage 2: GFR 60-89, Stage 3: GFR 30-59, Stage 4: GFR 15-29, Stage 5: GFR < 15

Question 60

Stage 1 CKD classification

Answer 60

Kidney damage with normal or increased GFR (GFR ≥ 90)

Question 61

Definition of Stage 2 CKD

Answer 61

Kidney damage with normal or decreased GFR (GFR 60-89)

Question 62

Definition of Stage 3 CKD

Answer 62

Moderate decreased GFR (GFR 30-59)

Question 63

Definition of Stage 4 CKD

Answer 63

Severe decreased GFR (GFR 15-29)

Question 64

Definition of Stage 5 CKD

Answer 64

Kidney failure with GFR < 15