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
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)
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)
4
Q
What are the most important NPNs
A
- BUN (Blood Urea Nitrogen)
- Creatinine
- Uric acid
- Ammonia
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%)
6
Q
What replaced the measurement of NPN?
A
determination of blood urea nitrogen (BUN)
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
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)
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
10
Q
Normal value of urea
A
• Normal value: 10–50 mg/dL
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
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
13
Q
Plasma BUN Concentration is determined by:
A
- Renal function
- Dietary protein intake
- Protein catabolism rate
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
15
Q
Pre-renal causes (ie blood vessels) of Hyperuremia or increased BUN
A
(Sometimes translates into dehydration) • ↓ Renal blood flow (e.g. CHF & dehydration) • ↑ Protein catabolism (as in fever) • High protein diet • Corticosteroid drugs
16
Q
Renal/within the kidney causes of hyperuremia have usually what
A
Co-morbidity with other diseases
17
Q
Renal causes of HYPERUREMIA
A
- Acute and chronic renal failure (associated with diabetes mellitus)
- Glomerular nephritis
- Tubular necrosis
- Malignant hypertension
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
19
Q
A decrease in BUN is associated with
A
Hypouremia
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
21
Q
It is the elevated urea concentration in blood (>20mg/dL)
A
Azotemia
22
Q
T or F: Azotemia is always due to kidney dysfunction
A
False
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
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))
25
Pre-renal causes of AZOTEMIA
* Congestive heart failure
* Shock
* Hemorrhage
* Dehydration
* High-protein diet
* Increased catabolic states (e.g. fever, major illness, stress)
26
Why does decreased renal function (glomerular filtration) lead to increased blood urea?
Poor excretion
27
Renal causes of AZOTEMIA
* Acute & chronic renal failure
* Glomerulonephritis
* Nephrotic syndrome
* Tubular necrosis
* Other intrinsic renal diseases
28
Post-renal causes of AZOTEMIA are usually due to
Obstruction of renal flow (renal calculi/kidney stones)
• Tumors of the bladder or prostate
• Severe infections (UTI)
29
T or F: BUN is more susceptible to non-renal functions
True
30
Reference ranges for BUN
Reference range: 7–18 mg/dL
31
Specimen requirements for BUN
* Plasma
* Serum
* 24-hour Urine Collection
* Non-hemolyzed (Hemolysis can increase BUN)
32
Methods used for BUN
```
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
```
33
How is BUN converted to urea?
Urea nitrogen concentration can be converted to urea concentration by multiplying by 2.14
(See trans for example)
34
Methodology for conversion of BUN to urea
* 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)
35
Reference Range of Urea N
* Serum or Plasma: 6–20 mg/dL
| * 24 hours urine: 12–20 grams/day
36
(See trans for bun/creatinine ratio)
(See trans for bun/creatinine ratio)
37
What are the sources of creatine in the liver?
arginine, glycine, and methionine
38
Creatine is converted to
Creatine phosphate (High energy source for muscle tissues)
39
Where does creatinINe come from?
produced as a waste product of creatine and creatine phosphate in muscles
Creatine Phosphate – Phosphoric Acid = Creatinine
Creatine – Water = Creatinine
40
When is creatine elevated in plasma and urine?
muscular dystrophy, hyperthyroidism, trauma
| Specialized testing; not part of routine lab
41
Internal anhydride derived from dephosphorylation of creatine phosphate and a metabolic product cleared entirely by the glomerular filtration
Creatinine
42
T or F: creatinine is not reabsorbed
True
| Neither secreted nor absorbed by renal tubules
43
What must happen in order to see increased creatinine in serum?
50% kidney function is lost
44
What affects creatinine?
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)
45
Advantages of testing creatinine for renal function
* Formed at a constant rate
* Readily excreted
* Not reabsorbed
* Not affected by diet
46
How is creatinine formed in the liver?
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
Measurement of creatinine concentration is used to determine
* Sufficiency of kidney function
* Severity of kidney damage
* Monitor the progression of kidney disease
48
the most common test to evaluate renal function
Plasma creatinine (very stable from day to day; delta check= should be investigated; urinary levels not normal)
49
What causes increased creatinine?
* 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
Normal values for creatinine
* 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
Specimen requirements for creatinine
```
Serum
Plasma
Urine
No icterus
No hemolysis
```
52
Classical technique and most frequently used in determining creatinine wherein elevated bilirubin and hemolysis causes falsely decreased result
Jaffe reaction
53
[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+
Enzymatic method
54
[Creatinine Methodology]
| Creatinine+picric acid (alkaline) > redorange chromogen
Jaffe method
55
[Creatinine Methodology]
| Part of creatinine methodology wherein rate of change in absorbance is measured
Kinetic jaffe reaction
56
[Creatinine Methodology]
| Principle of kinetic jaffe reaction
Protein-free filtrate (serum/urine) mixed with alkaline picrate solution forms yelloworange complex of creatinine picrate (absorbs light at 520nm)
57
[Creatinine Methodology]
| What are the kind of interferences kinetic jaffe reaction are subjected to
proteins, glucose, uric acid, medications and others (alpha-keto acids and cephalosporins)
58
Creatinine reference ranges for jaffe method (plasma)
(mg/dL)
Male: 0.9-1.3
Female: 0.6-1.1
Child: 0.3-0.7
59
Creatinine reference ranges for enzymatic method (plasma)
Male: 0.6-1.1
Female: 0.5-0.8
Child: 0-0.6
60
[Creatine Assay]
| What is creatinine concentration?
Difference arising from heating creatine which turns into creatinine
61
What is the solution in heating and method used in creatine assay?
Acid solution
| Endpoint jaffe method
62
volume of plasma from which a measured amount of substance can be completely eliminated into urine per unit of time (ml/min)
Clearance
| rate that creatinine and urea are cleared from the body
63
T or F: Creatinine clearance is a measurement of glomerular filtration (renal function)
True (good test)
64
T or F: Plasma creatinine is directly proportional to creatinine clearance
False (inversely)
65
Why is creatinine clearance a good test for glomerular filtration (estimation of GFR)?
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
volume of plasma filtered by the glomerulus per unit time
Glomerular filtration rate
67
What is the most sensitive measure of kidney function?
Creatinine clearance
68
T or F: Urine specimen for creatinine clearance can be unrefrigerated
False, refrigerated 24 hr urine
| *serum/plasma collected during 24-hr urine collxn
69
reference ranges for CREATININE CLEARANCE
| see case examples
males: 97-137 ml/min
females: 88-128 ml/min
70
What are some drawbacks to creatinine clearance
* 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
uric acid is present in the plasma as
monosodium urate
72
T or F: uric acid is relatively solule in plasma pH levels
false, insoluble
73
What can happen if plasma uric acid is elevated (>6.8 mg/dl)?
promote formation of solid uric acid crystals in joints and urine
74
T or F: creatinine is measuredto assess inherited disorders of purine metabolism
False, uric acid
75
Uric acid is measured to confirm diagnosis and monitor treatment of?
gout
76
Other purposes of measuring uric acid
* To assist in the diagnosis of renal calculi
* To prevent uric acid nephropathy during chemotherapeutic treatment
* To detect kidney dysfunction
77
It is the final breakdown product of nucleic acid catabolism (purine metabolism)
uric acid
| purines: adenine/guanine >uric acid by liver
* see uric acid formation
78
What % of uric acid is transported to kidney and filtered?
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
T or F: majority of uric acid is filtered by the glomerulus and reabsorbed
True (98-100%)
80
hyperuricemia can be explained by:
• Gout
• Pregnancy toxemia
• Increased catabolism
(Chemotherapy for diseases such as leukemia & multiple myeloma and Allopurinol)
• Chronic renal disease (hinders filtration and secretion)
81
hypouricemia is secondary to what?
severe liver disease
| usually due to defective renal tubular reabsorption
82
If a patient do not resorb uric acid/hypouricemic what is the kind of anemia that occurs?
Fanconi's syndrome
83
Which chemotherapy drug inhibits purine synthesis in hypouricemia?
6-mercaptopurine or azathioprine
84
drug which promotes uric acid excretion in hypouricemia?
uricosuric drugs (ie: salicylate)
85
How does allopurinol increase catabolism in hypouricemia?
It inhibits xanthine oxidase, an enzyme in the uric acid synthesis pathway, is used to treat these patients
86
Other causes of increased uric acid
* Leukemias and lymphomas (↑ DNA catabolism)
* Megaloblastic anemia (↑ DNA catabolism)
* Renal disease (but not very specific)
87
Uric acid levels for gout
> 6.0 mg/dL
88
What is gout?
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
Goat can increase risk of
renal calculi and kidney stones
*associated with alcohol consumption
90
Reference ranges for uric acid
Male: 2.5 – 6 mg/dL
Female: 2–5 mg/dL
91
Why should lipemia be avoided in specimens for uric acid?
High bilirubin may falsely decrease results by peroxidase methods
92
Classical chemical method for uric acid determination
Phosphotungstic Acid Reduction
| • Urate reduces phosphotungsic acid to a blue phosphotungstate complex, which is measured spectrophotometrically
93
primary method for uric acid determination
uricase method
| uses added enzyme uricase/urate oxidsase which catalyzes oxidation of urate to allantoin, H2O2 and CO2
94
T or F: allantoin does not absorb light at 293 nm
true,
| uric acid does
95
reference ranges for URIC ACID
* Males: 3.5–7.2 mg/dL
| * Females: 2.6–6.0 mg/dL
96
Where does ammonia come from?
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
What happens in the liver when ammonia is metabolized?
consumed by parenchymal cells and converted to urea (less toxic and can be removed from plasma via kidneys)
98
T or F: Free ammonia is non-toxic
False, ammonia is present in plasma in low concentrations
99
Uses of ammonia measurement
* Diagnose of inherited deficiencies of urea cycle enzymes
| * Diagnose and monitor treatment
100
What is the most common cause of abnormal ammonia levels?
Severe liver disease
*ammonia is not removed from circulation and not converted to urea
101
Elevated ammonia levels are neurotoxic because ammonia passes through blood-brain barrier
Hepatic Encephalopathy
102
This is most commonly seen in children and is often preceded by viral infxn treated with aspirin (ie RSV)
Reye's Syndrome
*sever fatty infiltration of liver
103
reference ranges for ammonia
19-60 micrograms/dL
104
Specimen requirements for AMMONIA determination
Whole blood (EDTA/heparin); should not smoke several hours prior to collxn; testing is difficult (easy contamination)
105
Historical methods of determining ammonia
* Conway (1935) – volatilize, absorbed then titrated
| * Dowex 50 cation-exchange column + Berthelot reaction
106
Why is Glutamate Dehydrogenase (GLDH) decreased in absorbance at 340 nm?
NADPH is consumed (oxidized) (see eqn)
*NADP+ is measured at 340 and proportional to ammonia
107
In determining GLDH, what specimen is used
EDTA or Heparinized Whole Blood on ice
| Must be tested ASAP or plasma frozen; Delayed testing caused false increased values
108
reference ranges for GLDH
20-60 micrograms/dL
109
Change in pH of solution as ammonia diffuses through semipermeable
membrane
Direct ISE
110
Other screening tests for renal disease
urinalysis (good indicator) and microalbumin (albumin: sign of renal disease and usually performed on random urine)
111
REMEMBER RENAL PANEL!
* Albumin
* Chloride
* Glucose
* Potassium
* BUN
* Carbon dioxide
* Creatinine
* Sodium
* Calcium
* Phosphorus
112
(see NPN top 10 and summary of ref ranges)
(see NPN top 10 and summary of ref ranges)
