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Clinical Chemistry > Non-protein Nitrogen Compounds > Flashcards

Non-protein Nitrogen Compounds Flashcards

1
Q

Describe non-protein nitrogen compounds

A

General term that can be used for different substances that have the element nitrogen in them, but are not proteins

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2
Q

Non-protein nitrogen compounds are products of what?

A

Products from the catabolism of proteins and nucleic acids which includes about 15 different substances (/compounds: NPN fraction)

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3
Q

Non-protein nitrogen compounds are used in evaluating

A

Renal function and excretion (plasma npns increased in renal failure; ordered as blood tests)

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4
Q

What are the most important NPNs

A
  • BUN (Blood Urea Nitrogen)
  • Creatinine
  • Uric acid
  • Ammonia
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5
Q

Major components of NPN with plasma concenctration (%plasma npn)

A
  • Urea: associated with urine and fertilizer (BUN: 45%)
  • Uric acid: increases with intake of protein (20%)
  • Creatinine (5%)
  • Creatine: component of whey protein (1-5%)
  • Amino acids (20%)
  • Ammonia (0.2%)
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6
Q

What replaced the measurement of NPN?

A

determination of blood urea nitrogen (BUN)

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7
Q

It is the nitrogenous end-product of protein or amino acid and nucleic acid metabolism which constitutes 45-50% of NPN

A

Urea

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8
Q

How is urea synthesized in the liver?

A

Synthesized in the liver when NH3 is removed and combined with CO2 (Ammonia is very toxic so it is converted to urea)

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9
Q

Other characteristics of urea

A
  • Excreted by glomerular filtration and partially reabsorbed through renal tubules
  • Rises quickly as compared to creatinine
  • Majority excreted in urine
  • Most widely used screening test of kidney function
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10
Q

Normal value of urea

A

• Normal value: 10–50 mg/dL

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11
Q

Highest concentration of NPN in blood and a major excretory product of protein metabolism (processes which release nitrogen, which is converted to ammonia and synthesized again in the liver from CO2 and ammonia that arises from deamination of amino acids)

A

Blood urea nitrogen

BUN=urea determination

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12
Q

BUN is excreted by what organ?

A

Kidneys
• Filtered by the glomerulus but 40% is reabsorbed by the renal tubules
• <10% of the total are excreted through the gastrointestinal tract and skin

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13
Q

Plasma BUN Concentration is determined by:

A
  • Renal function
  • Dietary protein intake
  • Protein catabolism rate
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14
Q

[Clinical significance of BUN)

Measurement of urea is used to:

A
  • Evaluate renal function
  • Assess hydration status
  • Determine nitrogen balance
  • Aid in the diagnosis of renal disease
  • Verify adequacy of dialysis
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15
Q

Pre-renal causes (ie blood vessels) of Hyperuremia or increased BUN

A 
(Sometimes translates into dehydration)
• ↓ Renal blood flow (e.g. CHF &amp; dehydration)
• ↑ Protein catabolism (as in fever) 
• High protein diet
• Corticosteroid drugs
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16
Q

Renal/within the kidney causes of hyperuremia have usually what

A

Co-morbidity with other diseases

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17
Q

Renal causes of HYPERUREMIA

A
  • Acute and chronic renal failure (associated with diabetes mellitus)
  • Glomerular nephritis
  • Tubular necrosis
  • Malignant hypertension
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18
Q

Post-renal (outside the kidney) causes of HYPERUREMIA are usually associated with

A 
Obstruction:
• Urethral stones
• Tumors of bladder
• Prostate enlargement
• Cervical cancer
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19
Q

A decrease in BUN is associated with

A

Hypouremia

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20
Q

Symptoms of hypouremia

A
  • Liver failure or severe liver disease (lack of urea synthesis)
  • Severe vomiting and/or diarrhea
  • Decreased dietary protein
  • Increased protein synthesis (observed in pregnant women and children)
  • Malnutrition (e.g. Kwashiorkor)
  • Overhydration
  • Early and late stages of pregnancy
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21
Q

It is the elevated urea concentration in blood (>20mg/dL)

A

Azotemia

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22
Q

T or F: Azotemia is always due to kidney dysfunction

A

False

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23
Q

Very high plasma urea concentration accompanied with renal failure

A

Uremic Syndrome or Uremia
• Urea crosses the blood-brain barrier which is used by the brain for energy (Leads to confusion, lethargy, and comatose)
• Uremic pericarditis: presence of heart murmurs

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24
Q

What is the mechanism of azotemia in pre-renal causes?

A

Reduced renal blood flow > less blood is delivered to the kidney > less urea filtered
(Anything that causes a decrease in functional blood volume (low blood pressure))

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25
Q

Pre-renal causes of AZOTEMIA

A
  • Congestive heart failure
  • Shock
  • Hemorrhage
  • Dehydration
  • High-protein diet
  • Increased catabolic states (e.g. fever, major illness, stress)
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26
Q

Why does decreased renal function (glomerular filtration) lead to increased blood urea?

A

Poor excretion

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27
Q

Renal causes of AZOTEMIA

A
  • Acute & chronic renal failure
  • Glomerulonephritis
  • Nephrotic syndrome
  • Tubular necrosis
  • Other intrinsic renal diseases
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28
Q

Post-renal causes of AZOTEMIA are usually due to

A

Obstruction of renal flow (renal calculi/kidney stones)
• Tumors of the bladder or prostate
• Severe infections (UTI)

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29
Q

T or F: BUN is more susceptible to non-renal functions

A

True

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30
Q

Reference ranges for BUN

A

Reference range: 7–18 mg/dL

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31
Q

Specimen requirements for BUN

A
  • Plasma
  • Serum
  • 24-hour Urine Collection
  • Non-hemolyzed (Hemolysis can increase BUN)
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32
Q

Methods used for BUN

A 
Kjeldahl method (classical, measures nitrogen)
Berthelot reaction (manual, uses urease to split off ammonia and produce color rxn)
Diacetyl monoxide (or monoxime) (popular but not manual, uses strong acids and oxidizing chemicals
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33
Q

How is BUN converted to urea?

A

Urea nitrogen concentration can be converted to urea concentration by multiplying by 2.14
(See trans for example)

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34
Q

Methodology for conversion of BUN to urea

A
  • Enzymatic (Most common method that couples the urease reaction with glutamate dehydrogenase, see trans)
  • Indicator Dye (Addition of PH indicator to ammonium ion results to color change)
  • Conductimetric (Conversion of unionized urea to NH4+ and CO32- results in increased conductivity)
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35
Q

Reference Range of Urea N

A
  • Serum or Plasma: 6–20 mg/dL

* 24 hours urine: 12–20 grams/day

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36
Q

(See trans for bun/creatinine ratio)

A

(See trans for bun/creatinine ratio)

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37
Q

What are the sources of creatine in the liver?

A

arginine, glycine, and methionine

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38
Q

Creatine is converted to

A

Creatine phosphate (High energy source for muscle tissues)

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39
Q

Where does creatinINe come from?

A

produced as a waste product of creatine and creatine phosphate in muscles
Creatine Phosphate – Phosphoric Acid = Creatinine
Creatine – Water = Creatinine

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40
Q

When is creatine elevated in plasma and urine?

A

muscular dystrophy, hyperthyroidism, trauma

Specialized testing; not part of routine lab

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41
Q

Internal anhydride derived from dephosphorylation of creatine phosphate and a metabolic product cleared entirely by the glomerular filtration

A

Creatinine

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42
Q

T or F: creatinine is not reabsorbed

A

True

Neither secreted nor absorbed by renal tubules

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43
Q

What must happen in order to see increased creatinine in serum?

A

50% kidney function is lost

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44
Q

What affects creatinine?

A

Creatinine levels are affected by muscle mass, creatine turnover, and renal function
(Released into circulation at a stable rate proportional to muscle mass; excreted in urine)

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45
Q

Advantages of testing creatinine for renal function

A
  • Formed at a constant rate
  • Readily excreted
  • Not reabsorbed
  • Not affected by diet
46
Q

How is creatinine formed in the liver?

A

Amino acids > creatine(transported to other tissues such as muscles)> phosphocreatine or creatine phosphate > creatinine (@ muscles)
• Phosphocreatine loses phosphoric acid and creatine loses water to form the cyclic compound, creatinine

47
Q

Measurement of creatinine concentration is used to determine

A
  • Sufficiency of kidney function
  • Severity of kidney damage
  • Monitor the progression of kidney disease
48
Q

the most common test to evaluate renal function

A

Plasma creatinine (very stable from day to day; delta check= should be investigated; urinary levels not normal)

49
Q

What causes increased creatinine?

A
  • Abnormal renal function
  • Renal disease
  • Decrease in glomerular filtration rate (GFR) (May be 50% of normal before plasma creatinine is elevated)
  • Urinary obstruction
  • Decreased muscle mass (e.g. muscular dystrophy)
  • Hyperthyroidism
  • Trauma
50
Q

Normal values for creatinine

A
  • Male: 0.7–1.36 mg/dL
  • Female: 0.6–1.13 mg/dL
  • Urine: 0.8–2.0 grams / 24 hours
  • Serum: 0.5–1.5 mg/dL
51
Q

Specimen requirements for creatinine

A 
Serum
Plasma
Urine
No icterus
No hemolysis
52
Q

Classical technique and most frequently used in determining creatinine wherein elevated bilirubin and hemolysis causes falsely decreased result

A

Jaffe reaction

53
Q

[Creatinine Methodology]
Creatinine+H2O (creatininase) > Creatine Creatine+ATP (creatine kinase) > Creatine Phosphate+ADP
ADP+PEP (pyruvate kinase) > ATP+Pyruvate Pyruvate+NADH+H+ (LDH) > Lactate+H+

A

Enzymatic method

54
Q

[Creatinine Methodology]

Creatinine+picric acid (alkaline) > redorange chromogen

A

Jaffe method

55
Q

[Creatinine Methodology]

Part of creatinine methodology wherein rate of change in absorbance is measured

A

Kinetic jaffe reaction

56
Q

[Creatinine Methodology]

Principle of kinetic jaffe reaction

A

Protein-free filtrate (serum/urine) mixed with alkaline picrate solution forms yelloworange complex of creatinine picrate (absorbs light at 520nm)

57
Q

[Creatinine Methodology]

What are the kind of interferences kinetic jaffe reaction are subjected to

A

proteins, glucose, uric acid, medications and others (alpha-keto acids and cephalosporins)

58
Q

Creatinine reference ranges for jaffe method (plasma)

A

(mg/dL)
Male: 0.9-1.3
Female: 0.6-1.1
Child: 0.3-0.7

59
Q

Creatinine reference ranges for enzymatic method (plasma)

A

Male: 0.6-1.1
Female: 0.5-0.8
Child: 0-0.6

60
Q

[Creatine Assay]

What is creatinine concentration?

A

Difference arising from heating creatine which turns into creatinine

61
Q

What is the solution in heating and method used in creatine assay?

A

Acid solution

Endpoint jaffe method

62
Q

volume of plasma from which a measured amount of substance can be completely eliminated into urine per unit of time (ml/min)

A

Clearance

rate that creatinine and urea are cleared from the body

63
Q

T or F: Creatinine clearance is a measurement of glomerular filtration (renal function)

A

True (good test)

64
Q

T or F: Plasma creatinine is directly proportional to creatinine clearance

A

False (inversely)

65
Q

Why is creatinine clearance a good test for glomerular filtration (estimation of GFR)?

A

creatinine is an endogenous substance (not affected by diet) and it is filtered by glomerulus, but not secreted or reabsorbed by the renal tubules

66
Q

volume of plasma filtered by the glomerulus per unit time

A

Glomerular filtration rate

67
Q

What is the most sensitive measure of kidney function?

A

Creatinine clearance

68
Q

T or F: Urine specimen for creatinine clearance can be unrefrigerated

A

False, refrigerated 24 hr urine

*serum/plasma collected during 24-hr urine collxn

69
Q

reference ranges for CREATININE CLEARANCE

see case examples

A

males: 97-137 ml/min
females: 88-128 ml/min

70
Q

What are some drawbacks to creatinine clearance

A
  • Overestimates GFR by 10–20%
  • Timing of serum or urine collection for accurate analysis
  • Patients or health care workers must follow detailed instructions for proper collection
71
Q

uric acid is present in the plasma as

A

monosodium urate

72
Q

T or F: uric acid is relatively solule in plasma pH levels

A

false, insoluble

73
Q

What can happen if plasma uric acid is elevated (>6.8 mg/dl)?

A

promote formation of solid uric acid crystals in joints and urine

74
Q

T or F: creatinine is measuredto assess inherited disorders of purine metabolism

A

False, uric acid

75
Q

Uric acid is measured to confirm diagnosis and monitor treatment of?

76
Q

Other purposes of measuring uric acid

A
  • To assist in the diagnosis of renal calculi
  • To prevent uric acid nephropathy during chemotherapeutic treatment
  • To detect kidney dysfunction
77
Q

It is the final breakdown product of nucleic acid catabolism (purine metabolism)

A

uric acid

purines: adenine/guanine >uric acid by liver
* see uric acid formation

78
Q

What % of uric acid is transported to kidney and filtered?

A

70%
(98% reabsorbed in proximal convoluted tubule (PCT); Some secreted by distal convoluted tubule (DCT); Net amount 6-12% of filtered amount)
*30% @ GIT

79
Q

T or F: majority of uric acid is filtered by the glomerulus and reabsorbed

A

True (98-100%)

80
Q

hyperuricemia can be explained by:

A

• Gout
• Pregnancy toxemia
• Increased catabolism
(Chemotherapy for diseases such as leukemia & multiple myeloma and Allopurinol)
• Chronic renal disease (hinders filtration and secretion)

81
Q

hypouricemia is secondary to what?

A

severe liver disease

usually due to defective renal tubular reabsorption

82
Q

If a patient do not resorb uric acid/hypouricemic what is the kind of anemia that occurs?

A

Fanconi’s syndrome

83
Q

Which chemotherapy drug inhibits purine synthesis in hypouricemia?

A

6-mercaptopurine or azathioprine

84
Q

drug which promotes uric acid excretion in hypouricemia?

A

uricosuric drugs (ie: salicylate)

85
Q

How does allopurinol increase catabolism in hypouricemia?

A

It inhibits xanthine oxidase, an enzyme in the uric acid synthesis pathway, is used to treat these patients

86
Q

Other causes of increased uric acid

A
  • Leukemias and lymphomas (↑ DNA catabolism)
  • Megaloblastic anemia (↑ DNA catabolism)
  • Renal disease (but not very specific)
87
Q

Uric acid levels for gout

A

> 6.0 mg/dL

88
Q

What is gout?

A

Pain and inflammation of joints by precipitation of sodium urates in tissues/ Painful uric acid crystals in joints occuring primarily in men with onset at 30-50 yrs

89
Q

Goat can increase risk of

A

renal calculi and kidney stones

*associated with alcohol consumption

90
Q

Reference ranges for uric acid

A

Male: 2.5 – 6 mg/dL
Female: 2–5 mg/dL

91
Q

Why should lipemia be avoided in specimens for uric acid?

A

High bilirubin may falsely decrease results by peroxidase methods

92
Q

Classical chemical method for uric acid determination

A

Phosphotungstic Acid Reduction

• Urate reduces phosphotungsic acid to a blue phosphotungstate complex, which is measured spectrophotometrically

93
Q

primary method for uric acid determination

A

uricase method

uses added enzyme uricase/urate oxidsase which catalyzes oxidation of urate to allantoin, H2O2 and CO2

94
Q

T or F: allantoin does not absorb light at 293 nm

A

true,

uric acid does

95
Q

reference ranges for URIC ACID

A
  • Males: 3.5–7.2 mg/dL

* Females: 2.6–6.0 mg/dL

96
Q

Where does ammonia come from?

A

codeamination of amino acids in the muscle (during exercise) and from digestive and bacterial enzymes in the GI tract
(If the patient has hepatic encephalopathy, administer
defecation, hydration, paracetamol, antibiotics)

97
Q

What happens in the liver when ammonia is metabolized?

A

consumed by parenchymal cells and converted to urea (less toxic and can be removed from plasma via kidneys)

98
Q

T or F: Free ammonia is non-toxic

A

False, ammonia is present in plasma in low concentrations

99
Q

Uses of ammonia measurement

A
  • Diagnose of inherited deficiencies of urea cycle enzymes

* Diagnose and monitor treatment

100
Q

What is the most common cause of abnormal ammonia levels?

A

Severe liver disease

*ammonia is not removed from circulation and not converted to urea

101
Q

Elevated ammonia levels are neurotoxic because ammonia passes through blood-brain barrier

A

Hepatic Encephalopathy

102
Q

This is most commonly seen in children and is often preceded by viral infxn treated with aspirin (ie RSV)

A

Reye’s Syndrome

*sever fatty infiltration of liver

103
Q

reference ranges for ammonia

A

19-60 micrograms/dL

104
Q

Specimen requirements for AMMONIA determination

A

Whole blood (EDTA/heparin); should not smoke several hours prior to collxn; testing is difficult (easy contamination)

105
Q

Historical methods of determining ammonia

A
  • Conway (1935) – volatilize, absorbed then titrated

* Dowex 50 cation-exchange column + Berthelot reaction

106
Q

Why is Glutamate Dehydrogenase (GLDH) decreased in absorbance at 340 nm?

A

NADPH is consumed (oxidized) (see eqn)

*NADP+ is measured at 340 and proportional to ammonia

107
Q

In determining GLDH, what specimen is used

A

EDTA or Heparinized Whole Blood on ice

Must be tested ASAP or plasma frozen; Delayed testing caused false increased values

108
Q

reference ranges for GLDH

A

20-60 micrograms/dL

109
Q

Change in pH of solution as ammonia diffuses through semipermeable
membrane

A

Direct ISE

110
Q

Other screening tests for renal disease

A

urinalysis (good indicator) and microalbumin (albumin: sign of renal disease and usually performed on random urine)

111
Q

REMEMBER RENAL PANEL!

A
  • Albumin
  • Chloride
  • Glucose
  • Potassium
  • BUN
  • Carbon dioxide
  • Creatinine
  • Sodium
  • Calcium
  • Phosphorus
112
Q

(see NPN top 10 and summary of ref ranges)

A

(see NPN top 10 and summary of ref ranges)

Clinical Chemistry (9 decks)

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