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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
Q

Normal ratio of BUN: creatinine

A

12:1-20:1

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26
Q

Specific cause for a constant ratio of 10:1-15:1 in the BUN:creatinine ratio

A

Patient probably has intrinsic renal disease

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27
Q

Uric acid

- One specific pathologic source

A

Catabolism of the purine base nucleosides, adenoside, and guanosine (= purine base metabolism)

28
Q

Uric acid

- Two specific normal sources

A
  • Food

- Conditions of increased nucleic acid turnover (cancer patients)

29
Q

Uric acid

- Four sequential steps in its renal handling

A
  • Free glomerular filtration
  • Reabsorption of >90% in PCT
  • Tubular secretion in the distal portion of the PCT
  • Reabsorption in the DCT
30
Q

Uric acid

- Two primary causes of hyperuricemia associated w/ increased formation

A
  • Idiopathic

- Inherited metabolic disorders

31
Q

Uric acid

- Five secondary causes of hyperuricemia associated w/ increased formation

A
  • Excess dietary purine intake
  • Increased nucleic acid turnover (chemotherapy, radiotherapy, myeloma, leukemia, trauma)
  • Altered ATP metabolism (alcohol toxicity, tissue hypoxia)
  • Preeclampsia
  • Down Syndrome
32
Q

Uric acid

- One primary cause associated w/ decreased excretion

A

Idiopathic

33
Q

Uric acid

- Causes of primary gout

A
  • Overproduction of purines
  • Decreased renal secretion of uric acid
  • Increased dietary intake of purines (problem handling uric acid)
34
Q

Uric acid

- Causes of secondary gout

A
  • Consumption of alcohol
  • Fructose drinks
  • Meat and seafood (dietary gout, acute/chronic renal disease)
35
Q

Uric acid

- Reference range for men and women

A
  • Men: 4.0-8.5 mg/dL

- Women: 2.7-7.3 mg/dL

36
Q

Reagents used and scientist’s name associated w/ the chemical method for uric acid

A

Caraway method

- Oxidation of uric acid w/ reduction of phosphotungstic acid to tungsten blue

37
Q

Reagents used in the enzymatic method for uric acid

A

Uricase method → uricase oxidizes urate to allantoin

38
Q

Ammonia

- Three specific sources

A
  • 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
Q

Ammonia

- One primary cause of increased ammonia

A

Inherited urea cycle deficiencies

40
Q

Ammonia

-Three secondary causes of increased ammonia

A
  • Advanced liver disease and renal failure
  • Reye’s syndrome
  • Hepatic encephalopathy in individuals w/ cirrhosis
41
Q

Ammonia

- Four special collection and handling procedures

A
  • 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
Q

Ammonia

- Reference range

A

14-45 umol/L

43
Q

Uric acid

- Two general causes of hyperuricemia

A
  • Increased formation

- Decreased excretion

44
Q

Uric acid

- Five secondary causes of hyperuricemia associated w/ decreased excretion

A
  • 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
Q

Ammonia

- Reagents used in the enzymatic method

A

?

46
Q

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

A
  • Filtered: freely
  • Reabsorbed: PCT
  • Secretion: DCT
47
Q

The major nitrogen-containing byproduct of protien catabolism; ~75% of all NPNs excreted

A

BUN

48
Q

Higher-than-normal blood level of urea or other nitrogen-containing compounds; caused by inability of the kidneys to excrete NPNs

A

Azotemia

49
Q

What causes ↓ blood flow to the kidney, ↓ urea filtration, and subsequently ↑ urea levels in teh blood

A

Prerenal causes of azotemia

50
Q

What causes obstruction of urine flow in the urinary tract; ↓ excretion causes ↑ urea in the blood

A

Postrenal causes of azotemia

51
Q

Analytical methods for urea

A
  • Enzymatic

- Chemical

52
Q

Reagents used in the enzymatic methods for urea

A
  • (Berthelot rxn): phenol and hypochlorite

- Coupled enzymatic rxn of ammonium ion w/ glutamate dehydrogenase

53
Q

Reagent used in the chemical method for urea

A

Diazine

54
Q

Describe the metabolism of creatine and its importance in muscle contraction

A
  • 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
Q

A condition caused by hyperuricemia and deposition of uric acid crystals in joint and body fluids

A

Gout

56
Q

Describe primary gout

A
  • 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
Q

Consumption of coffee, vitamin C, and dairy products, as well as physical fitness appears to ____ risk of ____, probably due to decreasing insulin resistance

A

Decrease; gout

58
Q

Rate at which the kidneys are able to remove a filterable substance from the blood per unit of time

A

Clearance

59
Q

Clearance depends on what 2 things?

A
  • Plasma concentration of that substance

- Ability of kidneys to remove it

60
Q

3 reasons why creatinine is used, rather than urea, for glomerular function assessment

A
  • 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
Q

2 reasons why creatinine clearance calculation is used to assess glomerular function

A
  • Its production is faily constant day-to-day

- It’s freely filtered at the glomerulus and not secreted by teh renal tubules

62
Q

List the 3 instructions which should be given to a patient who is collecting a timed urine specimen

A
  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
Q

GFR equation

A

?

64
Q

Calculate a corrected creatinine clearance in mL/min

A

[(U/V)/P] x (1/t) x (1.73/SA)

65
Q

Calculate a creatinine excretion (“check”) in g/volume

A

[(UCR x TV x (1/1000) x (1/100)]

66
Q

State the usefulness of calculating creatinine excretion (“check”) in g/volume

A
  • 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
Q

List 2 compounds that may be used instead of creatinine when a more precise assessment of glomerular function is required

A
  • Inulin clearance

- Cystatin C

Liz's Clinical Chemistry Module 3 (7 decks)

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