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BUN (Blood Urea Nitrogen)
- Product of protein catabolism
- Filtered by the glomerulus but also reabsorbed by renal tubules
- Some is lost through the skin and the GI tract
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Plasma BUN is affected:
- Renal function
- Dietary protein
- Protein catabolism
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What are the most important NPN's?
- BUN (Blood Urea Nitrogen)
- Creatinine
- Uric acid
- Ammonia
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Azotemia
Elevated plasma BUN
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Disease correlations Prerenal increased BUN
- (Not related to renal function)
- Low Blood Pressure (CHF, Shock, hemorrhage, dehydration)
- Decreased blood flow to kidney (No filtration)
- Increased dietary protein
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Disease correlations Prerenal decreased BUN
- (Not related to renal function)
- Decreased dietary protein
- Increased protein synthesis (Pregnant women, children)
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Renal causes of increased BUN
- Renal disease with decreased glomerular filtration
- -Glmerular nephritis
- -Renal failure from Diabetes Mellitus
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Post renal causes of increased BUN
- (Not related to renal function)
- Obstruction of urine flow
- -Kidney stones
- -Bladder or prostate tumors
- -UTIs
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Normal BUN/Creatinine ratio
10 - 20 to 1
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Increased BUN
Normal Creatinine
- Pre-renal increased BUN/Creat ratio
- BUN is more susceptible to non-renal factors
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Increased BUN
Increased Creatinine
- Post-renal increased ratio BUN/Creat ratio
- Both BUN and Creat are elevated
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Decreased BUN
Normal Creatinine
- Renal decreased BUN/Creat ratio
- Low dietary protein or severe liver disease
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BUN analytical methods
- Specimen: plasma or serum
- To convert BUN to Urea: BUN x 2.14=Urea(mg/dl)
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Creatinine
- Plasma creatine is a function of glomerular filtration
- Unaffected by other factors
- It's a very good test to evaluate renal function
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Creatinine disease correlations
- Increased: decreased glomerular filtration (renal function)
- Plasma creatinine is unaffected by diet
- Very stable from day to day
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Jaffee Method
- Creatinin analytical technique
- Creatinine + Picrate Acid ---> Colored chromogen
- Specimen: Plasma or serum
- Elevated bilirubin and hemolysis causes falsely decreased results
- Reference range: 0.5 - 1.5 mg/dl
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Uric Acid
- Breakdown product of purines (nucleic acid/DNA)
- Purines from cellular breakdown are converted to uric acid by the liver
- Uric acid is filtered by the glomerulus
- Elevated plasma uric acid promote formation of solid uric acid crystals in joints and urine
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Uric acid diseases
- Increased plasma uric acid:
- Gout
- Leukemias and lymphomas (Increased DNA catabolism)
- Megaloblastic anemias (Increased DNA catabolism)
- Renal disease (but not very specific
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