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Liz's Clinical Chemistry Module 3 > Non-Protein Nitrogens and Glomerular Function Tests > Flashcards

Non-Protein Nitrogens and Glomerular Function Tests Flashcards

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1
Q

List the non-protein nitrogen compounds

A
  • Amino acids: 20%
  • Ammonia (deamination): 0.2%
  • Creatine (muscle contraction): 2%
  • Creatinine (muscle creatine): 5%
  • Urea (detoxification of ammonia): 45%
  • Uric acid (purine metabolism): 20%
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2
Q

2 specific sources of urea

A
  • Detoxification product of ammonia from the urea cycle

- Product of dietary protien intake

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3
Q

3 sites in the nephron where urea is filtered, reabsorbed, or secreted

A
  • Filtered: freely filtered in glomerulus
  • Reabsorbed: 40-50% in PCT
  • Secreted: Loops of Henle
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4
Q

Urea

- Relative usefulness for glomerular function assessment compared to creatinine

A

The BEST clinical use of BUN measurements lies w/ concomitant creatinine measurements

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5
Q

Urea

- 2 principal diagnostic uses of its measurement

A

Pre-renal and post-renal azotemia problems

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6
Q

Reference range of urea

A

8-26 mg/dL

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7
Q

5 factors that affect BUN levels

A
  • State of hydration (affects renal blood flow rate)
  • Renal function (but not until GFR falls to 50% of normal)
  • Liver funciona
  • Amount of protein in diet
  • Amount of protein breakdown body
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8
Q

5 conditions that increase the nitrogen load

A
  • Febrile illness
  • Corticosteroid or tetracycline therapy
  • Large protein ingestion
  • GI bleed w/ blood absorption in gut
  • Elevated thyroid hormone concentration
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9
Q

4 conditions that decrease the nitrogen load

A
  • Low protein diet
  • ↑ androgens
  • Growth hormone
  • Pregnancy
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10
Q

What test should be analyzed along w/ BUN in order to obtain the best assessment of renal function?

A

Creatinine

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11
Q

5 pre-renal causes of azotemia due to decreased blood flow to the kidney and decrease urea filtration

A
  • Congestive heart failure
  • Shock
  • Hemorrhage
  • Dehydration
  • Marked decrease in blood volume
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12
Q

What is one cause of renal azotemia?

A

Renal failure

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13
Q

What are the 3 causes of post-renal azotemia that cause decreased excretion of urea?

A
  • Reanl lithiasis (stones)
  • Tumors of the bladder or prostate
  • Severe infections
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14
Q

3 specific sources of creatine

A
  • Kidneys
  • Liver
  • Pancreas
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15
Q

Enzyme necessary for conversion of creatine to phosphocreatine

A

Creatine Kinase (CK)

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16
Q

1 specific source of creatinine

A

Anhydride byproduct of creatine

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17
Q

3 sites in the nephron where creatinine is filtered, reabsorbed, or secreted

A
  • Filtered: freely
  • Reabsorbed: not reabsorbed by tubules
  • Excreted: at constant rate w/ insignificant secretion
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18
Q

Creatinine

- 3 reasons why creatinine’s measurement may be used to estimate the GFR

A
  • Freely filtered by glomeruli
  • Not reabsorbed by tubules
  • Excreted at constant rate w/ insignificant secretion
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19
Q

Creatinine

- Usefulness for detecting early glomeruluar dysfunction

A
  • Detect kidney disease (decreases as disease worsens)
  • Monitor patients w/ known renal disease
  • Plan life sustaining therapy for those w/ end-stage renal disease
  • Adjust drug dosage for agents excreted by kidney
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20
Q

Creatinine

- Reference range for men and women

A
  • Men: 0.9-1.5 mg/dL

- Women: 0.8-1.2 mg/dL

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21
Q

4 clinical uses of GFR calculations

A
  • Detect kidney disease (decreases as disease worsens)
  • Monitor patients w/ known renal disease
  • Plan life sustaining therapy for those w/ end-stage renal disease
  • Adjust drug dosage for agents excreted by kidney
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22
Q

What chemical creatinine method has creatinine reacting directly w/ picrate ions under alkaline conditions to form a red-orange complex?

A

Principle of Jaffe creatinine method

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23
Q

Special reagents used in Jaffe creatinine method

A

Alkaline picrate ions

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24
Q

3 enzymes used for enzymatic determination of creatinine

A
  • Creatininase
  • Creatininase and creatinase
  • Creatinine iminohydrolase
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25
Normal ratio of BUN: creatinine
12:1-20:1
26
Specific cause for a constant ratio of 10:1-15:1 in the BUN:creatinine ratio
Patient probably has intrinsic renal disease
27
Uric acid | - One specific pathologic source
Catabolism of the purine base nucleosides, adenoside, and guanosine (= purine base metabolism)
28
Uric acid | - Two specific normal sources
- Food | - Conditions of increased nucleic acid turnover (cancer patients)
29
Uric acid | - Four sequential steps in its renal handling
- Free glomerular filtration - Reabsorption of >90% in PCT - Tubular secretion in the distal portion of the PCT - Reabsorption in the DCT
30
Uric acid | - Two primary causes of hyperuricemia associated w/ increased formation
- Idiopathic | - Inherited metabolic disorders
31
Uric acid | - Five secondary causes of hyperuricemia associated w/ increased formation
- Excess dietary purine intake - Increased nucleic acid turnover (chemotherapy, radiotherapy, myeloma, leukemia, trauma) - Altered ATP metabolism (alcohol toxicity, tissue hypoxia) - Preeclampsia - Down Syndrome
32
Uric acid | - One primary cause associated w/ decreased excretion
Idiopathic
33
Uric acid | - Causes of primary gout
- Overproduction of purines - Decreased renal secretion of uric acid - Increased dietary intake of purines (problem handling uric acid)
34
Uric acid | - Causes of secondary gout
- Consumption of alcohol - Fructose drinks - Meat and seafood (dietary gout, acute/chronic renal disease)
35
Uric acid | - Reference range for men and women
- Men: 4.0-8.5 mg/dL | - Women: 2.7-7.3 mg/dL
36
Reagents used and scientist's name associated w/ the chemical method for uric acid
Caraway method | - Oxidation of uric acid w/ reduction of phosphotungstic acid to tungsten blue
37
Reagents used in the enzymatic method for uric acid
Uricase method → uricase oxidizes urate to allantoin
38
Ammonia | - Three specific sources
- Deamination of proteins in the liver - Bacerial proteases, creases, and amine oxidases act on contents of colon in GI tract - Hydrolysis of the glutamine in both the small and large intestines
39
Ammonia | - One primary cause of increased ammonia
Inherited urea cycle deficiencies
40
Ammonia | -Three secondary causes of increased ammonia
- Advanced liver disease and renal failure - Reye's syndrome - Hepatic encephalopathy in individuals w/ cirrhosis
41
Ammonia | - Four special collection and handling procedures
- Good venipuncture technique must be used - Must be put on ice immediately and analyzed w/in 20 minutes of venipuncture - Patient must not smoke after midnight for a fasting specimen draw; no smoking in phlebotomy area - Lab area and glassware should be free from ammonia contamination
42
Ammonia | - Reference range
14-45 umol/L
43
Uric acid | - Two general causes of hyperuricemia
- Increased formation | - Decreased excretion
44
Uric acid | - Five secondary causes of hyperuricemia associated w/ decreased excretion
- Acute or chronic kidney disease - Increased renal reabsorption or reduced secretion - Lead poisoning (↑ PCT reabsorption, ↓ secretion of uric acid) - Preeclampsia (↑ PCT reabsorption) - Presence of organic acids (lactate or acetoacetate) (inhibits urate excretion)
45
Ammonia | - Reagents used in the enzymatic method
?
46
3 sites in the nephron where ammonia is filtered, reabsorbed, or secreted
- Filtered: freely - Reabsorbed: PCT - Secretion: DCT
47
The major nitrogen-containing byproduct of protien catabolism; ~75% of all NPNs excreted
BUN
48
Higher-than-normal blood level of urea or other nitrogen-containing compounds; caused by inability of the kidneys to excrete NPNs
Azotemia
49
What causes ↓ blood flow to the kidney, ↓ urea filtration, and subsequently ↑ urea levels in teh blood
Prerenal causes of azotemia
50
What causes obstruction of urine flow in the urinary tract; ↓ excretion causes ↑ urea in the blood
Postrenal causes of azotemia
51
Analytical methods for urea
- Enzymatic | - Chemical
52
Reagents used in the enzymatic methods for urea
- (Berthelot rxn): phenol and hypochlorite | - Coupled enzymatic rxn of ammonium ion w/ glutamate dehydrogenase
53
Reagent used in the chemical method for urea
Diazine
54
Describe the metabolism of creatine and its importance in muscle contraction
- Interconversion of phosphocreatine and creatine takes plce in muscle contraction - Amount of creatinine produced daily depends on muscle mass and animal muscle in the diet - Therefore, plasma levels do not vary greatly day-to-day
55
A condition caused by hyperuricemia and deposition of uric acid crystals in joint and body fluids
Gout
56
Describe primary gout
- Monosodium urate precipitates from supersaturated body fluids - Uric acid crystals deposit in joint fluids, as well in surrounding tissue, causing a characteristic inflammatory response and pain - Arises from enzyme deficiencies in catabolizing uric acid
57
Consumption of coffee, vitamin C, and dairy products, as well as physical fitness appears to ____ risk of ____, probably due to decreasing insulin resistance
Decrease; gout
58
Rate at which the kidneys are able to remove a filterable substance from the blood per unit of time
Clearance
59
Clearance depends on what 2 things?
- Plasma concentration of that substance | - Ability of kidneys to remove it
60
3 reasons why creatinine is used, rather than urea, for glomerular function assessment
- Majority of creatinine is handled in the glomerulus; BUN is reabsorbed adn secreted at other renal sites - Production of creatinine is fairly stable day-to-day (muscle mass doesn't change much on a daily basis); BUN is affected by state of hydration and dietary intake of protein - There aren't many diseases that affect muscular function (urea production is affected by liver function)
61
2 reasons why creatinine clearance calculation is used to assess glomerular function
- Its production is faily constant day-to-day | - It's freely filtered at the glomerulus and not secreted by teh renal tubules
62
List the 3 instructions which should be given to a patient who is collecting a timed urine specimen
1. Void into toilet and note the time 2. Collect every urine thereafter until the collection period is over, refrigerating specimen in b/w voids 3. At the end of the collection period, void and include this specimen in collection 4. Do NOT include first AND last voids
63
GFR equation
?
64
Calculate a corrected creatinine clearance in mL/min
[(U/V)/P] x (1/t) x (1.73/SA)
65
Calculate a creatinine excretion ("check") in g/volume
[(UCR x TV x (1/1000) x (1/100)]
66
State the usefulness of calculating creatinine excretion ("check") in g/volume
- Calculated to assess the "completeness" of a 24-hr urine collection, since creatinine production is fairly constant - If < 0.5, it's probably an incomplete collection
67
List 2 compounds that may be used instead of creatinine when a more precise assessment of glomerular function is required
- Inulin clearance | - Cystatin C

Liz's Clinical Chemistry Module 3 (7 decks)

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