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Diagnostic Studies, Unit III > BUN, Creatinine, Uric Acid > Flashcards

BUN, Creatinine, Uric Acid Flashcards

1
Q

Indications, BUN Testing

(3)

A

Evaluate the following:

  1. Kidney excretory function (esp in conjunction c creatinine)
  2. Liver function
  3. Hydration status
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2
Q

Test Explaination, BUN

A

**Measures the amount of urea nitrogen in the blood **

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3
Q

Blood Urea Formation

(6 steps)

A
  1. Protein metabolism to amino acids (from gut, working muscles, or kidney)
  2. Amino acid catabolism in liver
  3. Liver produce ammonia (toxic)
  4. Ammonia conversion to urea
  5. Urea transport thru bloodstream to kidneys
  6. Excretion in urine
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4
Q

Azotemia

A

The state of elevated BUN levels

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5
Q

Clinical Significance, Elevated BUN

A

Consider the following conditions:

  1. Liver disease
  2. Renal disease
    • ​pre-renal
    • intra-renal/parenchymal-renal
    • post-renal
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6
Q

Renal Parenchymal Disease

(cause)

A
  • Ultimately results from damage to kidney’s filtering structures
  • Nephrotoxicity/inflammation damages delicate nephron epithelial cells
  • Nephrotoxins also damage renal cortex, leading to acute renal failure

Major nephrotoxicity source - drugs that are cleared thru kidney

  • vancomycin
  • NSAIDs
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7
Q

Contributing Factors to Renal Parenchymal Disease

(6)

A
  1. Blood vessel disease
  2. Blood clot/injury in vessel in kidneys
  3. Injury to renal tissue and cells
  4. Glomerulonephritis
  5. Acute interstitial nephritis
  6. Acute tublar necrosis
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8
Q

Prerenal Azotemia

(definition, cause, 2 results)

A

Definition: increased BUN due to decreased flow to the kidneys

Cause: hypoperfusion → renal hypoxemia → decreased urea nitrogen clearance → increased BUN

Results:

  1. Decrased glomerular filtration rate
  2. Increased tubular reabsorption of Na and water
  3. Ultimately, electrolyte imbalance and metabolic acidosis
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9
Q

Conditions Causing Prerenal Azotemia

(3)

A
  1. Shock
  2. Dehydration
  3. CHF
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10
Q

Postrenal Azotemia

(definition, 3 causative categories, 1/2/3 specifics)

A

Definition: Azotemia from block in urine elmination from kidneys

Causes:

  1. Obstructed urethra
    • ​BPH
  2. Uni/bilateral ureter obstruction
    • ​Kidney stone
    • GU cancer
  3. Bladder obstruction
    • ​Bladder stone
    • Blood clot
    • Neurologic disorders of bladder contraction (ex: MS)
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11
Q

Relationship, Liver and BUN

A

Urea synthesis is liver-dependent

  • damination generates ammonia ion
  • hepatocyte enzymes convert ammonia ions into urea
  • remember, BUN = urea nitrogen

Liver disease decreases BUN levels

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12
Q

Deamination

A

Removal of amino group and hydrogen atom from proteins to create ammonia

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13
Q

Concomitant Liver and Renal Diseases

(effect on BUN)

A

In patients who have both liver and renal disease, BUN levels can be normal:

  • Poor hepatic function results in decreased formation of urea
  • Normal BUN levels in these patients are not an indicator of normal renal excretory function
    • ​Use creatinine to positively identify kidney dysfunction
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14
Q

Pathophysiology, Dehydration Increasing BUN levels

A
  1. General hypovolemia
  2. Decreased renal perfusion/pressure
  3. Decreased glomerular filtration rate
  4. Decreased renal urea excretion
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15
Q

Pathophysiology, CHF increasing BUN Levels

A
  1. Decreased cardiac ouput
  2. Decreased renal perfussion/pressure
  3. Decreased glomerular filtration rate
  4. Decreased renal urea excretion
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16
Q

Pathopysiology, GI Bleed/Excessive PRO Ingestions/Starvation Increasing BUN Levels

A
  1. Increased protein (and blood) catabolism
  2. Increased urea
  3. Kidney cannot keep up c excess material to excrete
17
Q

Pathophysiology, Sepsis Increasing BUN Levels

A
  1. Decreased renal perfusion/pressure
  2. Decreased glomerular filtration rate
  3. Decreased renal excretion of urea
  4. Increased blood urea nitrogen
18
Q

Indication, Creatine Testing

A

Dx or monitor impaired renal fctn

19
Q

Creatinine

A
  • Catabolic prdct of creatine phosphate
    • CP - high energy compound used in muscle contraction
  • Dependent on msucle mass
  • Excreted by kidneys
  • Directly proportional to renal excretory function
20
Q

Clinical Significance, Creatinine

A

If Cr is elevated, consider:

  • Renal parenchymal disease
  • Prerenal disease
  • Postrenal disease

Serum creatinine rises much LATER than BUN

  • Elevated Cr indicates CHRONIC disease or severe injury
21
Q

Serum Creatinine, Clinical Pearls

(2)

A
  1. Serum Cr is used in conjunction c BUN to estimate renal fctn
    • ​these two tests are always ordered together
  2. **Doubling serum Cr suggests a 50% glomerular filtration rate reduction **​​
    • ​s/sx may not be present at this time
22
Q

Increased Serum Creatinine

(3 causative categories, 1/4/1 specifics)

A
  1. Renal parenchymal disease
    • ​dysfunctional renal tissue
  2. Prerenal/postrenal disease
    • ​shock
    • dehydration
    • CHF
    • obstruction
  3. Rhabomyolysis
    • ​skeletal muscle injury
23
Q

Creatine Clerance

(definition, function, calculation)

A

Definition: mL filtrate made my kidneys/minute

Function: evaluate glomerular filtration rate (GFR)

Calculation: involves urine and serum creatinine

  • Often times labs will supply estimate
  • Calculation is usually limited to nephrologists
  • CrCl = Urine Cr (mg/dl) / Plasma Cr (mg/d)l x Ur volume (ml) / Collection period (mins)​
24
Q

Creatinine Value Variables

(5)

A
  1. Amount of blood flow to kidney
  2. Filtering capacity of glomerulous
  3. Age
    • ​CrCl decreases 6/5ml/min each c each decate post age 20
  4. Muscle mass
  5. Amt PRO in diet
25
Q

Abnormal Creatinine Explaination

(2 categories, 2/2)

A

**Incraesed Creatinine **(not always pathologic)

  • Exercise
  • Pregnancy

Decreased Creatinine

  • Impaired renal function
  • Prerenal etology
    • decraesed blood flow
    • decreased renal perfusion
    • decreased GFR
26
Q

Indications, Uric Acid

(2)

A
  1. Dx gout
  2. Evaluate pts c recurrent kidney stones (determine stone composition)
27
Q

Uric Acid

(definition, clearence, balance)

A

Definition: Waste product formed in liver during RNA purine recycling

Clearance: 75% excreted by kidney, 25% recycled to make new purine bases

Balance: level determiend by

  • liver synthesis rate
  • kidney excretion rate
28
Q

Clinical Significance, Increased Uric Acid

A

Causes of inc uric acid include

  1. Overproduction in **congenital enzyme deficiency **(rare)
  2. Increased purine/DNA turnover in cancer (most common)
  3. Increased muscle ATP during rhabdomyolysis
  4. Idiopathic (majority of cases)
29
Q

Decraesed Uric Acid Excretion

(3 causes)

A
  1. Gout (idiopathic)
  2. Chronic renal disease
  3. Alcoholism
    • ​accelerates ATP breakdown from liver → inc uric acid

Diagnostic Studies, Unit III (6 decks)

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