BUN, Creatinine, Uric Acid Flashcards
Indications, BUN Testing
(3)
Evaluate the following:
- Kidney excretory function (esp in conjunction c creatinine)
- Liver function
- Hydration status
Test Explaination, BUN
**Measures the amount of urea nitrogen in the blood **
Blood Urea Formation
(6 steps)
- Protein metabolism to amino acids (from gut, working muscles, or kidney)
- Amino acid catabolism in liver
- Liver produce ammonia (toxic)
- Ammonia conversion to urea
- Urea transport thru bloodstream to kidneys
- Excretion in urine
Azotemia
The state of elevated BUN levels
Clinical Significance, Elevated BUN
Consider the following conditions:
- Liver disease
- Renal disease
- pre-renal
- intra-renal/parenchymal-renal
- post-renal
Renal Parenchymal Disease
(cause)
- 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
Contributing Factors to Renal Parenchymal Disease
(6)
- Blood vessel disease
- Blood clot/injury in vessel in kidneys
- Injury to renal tissue and cells
- Glomerulonephritis
- Acute interstitial nephritis
- Acute tublar necrosis
Prerenal Azotemia
(definition, cause, 2 results)
Definition: increased BUN due to decreased flow to the kidneys
Cause: hypoperfusion → renal hypoxemia → decreased urea nitrogen clearance → increased BUN
Results:
- Decrased glomerular filtration rate
- Increased tubular reabsorption of Na and water
- Ultimately, electrolyte imbalance and metabolic acidosis
Conditions Causing Prerenal Azotemia
(3)
- Shock
- Dehydration
- CHF
Postrenal Azotemia
(definition, 3 causative categories, 1/2/3 specifics)
Definition: Azotemia from block in urine elmination from kidneys
Causes:
- Obstructed urethra
- BPH
- Uni/bilateral ureter obstruction
- Kidney stone
- GU cancer
- Bladder obstruction
- Bladder stone
- Blood clot
- Neurologic disorders of bladder contraction (ex: MS)
Relationship, Liver and BUN
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
Deamination
Removal of amino group and hydrogen atom from proteins to create ammonia
Concomitant Liver and Renal Diseases
(effect on BUN)
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
Pathophysiology, Dehydration Increasing BUN levels
- General hypovolemia
- Decreased renal perfusion/pressure
- Decreased glomerular filtration rate
- Decreased renal urea excretion
Pathophysiology, CHF increasing BUN Levels
- Decreased cardiac ouput
- Decreased renal perfussion/pressure
- Decreased glomerular filtration rate
- Decreased renal urea excretion
Pathopysiology, GI Bleed/Excessive PRO Ingestions/Starvation Increasing BUN Levels
- Increased protein (and blood) catabolism
- Increased urea
- Kidney cannot keep up c excess material to excrete
Pathophysiology, Sepsis Increasing BUN Levels
- Decreased renal perfusion/pressure
- Decreased glomerular filtration rate
- Decreased renal excretion of urea
- Increased blood urea nitrogen
Indication, Creatine Testing
Dx or monitor impaired renal fctn
Creatinine
- 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
Clinical Significance, Creatinine
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
Serum Creatinine, Clinical Pearls
(2)
- Serum Cr is used in conjunction c BUN to estimate renal fctn
- these two tests are always ordered together
- **Doubling serum Cr suggests a 50% glomerular filtration rate reduction **
- s/sx may not be present at this time
Increased Serum Creatinine
(3 causative categories, 1/4/1 specifics)
- Renal parenchymal disease
- dysfunctional renal tissue
- Prerenal/postrenal disease
- shock
- dehydration
- CHF
- obstruction
- Rhabomyolysis
- skeletal muscle injury
Creatine Clerance
(definition, function, calculation)
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)
Creatinine Value Variables
(5)
- Amount of blood flow to kidney
- Filtering capacity of glomerulous
- Age
- CrCl decreases 6/5ml/min each c each decate post age 20
- Muscle mass
- Amt PRO in diet
