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Interpretation of the BUN-to-creatinine Ratio
The principle behind this ratio is the fact that both urea (BUN) and creatinine are freely filtered by the glomerulus; however, urea reabsorbed by the tubules can be regulated (increased or decreased) whereas creatinine reabsorption remains the same (minimal reabsorption)
Increased ratio with normal creatinine level:
- prerenal uremia
- high protein intake
- GIT bleeding
Increased ratio with increased creatinine level:
- postrenal obstruction
Deacreased ratio:
- acute tubular necrosis
- low protein intake
- starvation
- severe liver disease
Classify renal function tests
Tests for screening kidney disease
- complete urine analysis
- plasma urea and creatinine
- plasma electrolytes
Tests to assess renal function:
- glomerular function:
GFR - clearance rate
glomerular permeability - proteinuria
- to assess tubular function:
reabsorption studies
secretion tests
concentration and dilution tests
renal acidification
Differentiate typical laboratory results of renal failure versus nephrotic syndrome
In nephrotic syndrome, urine protein excretion exceeds 3.5 g per day and is associated with edema, hypoalbuminemia, and hypercholesterolemia.
The presence of albuminuria on two occasions with the exclusion of a urinary tract infection indicates glomerular dysfunction. The presence of albuminuria for three or more months is indicative of chronic kidney disease.
GFR finding to classifly renal disease. Lower GFR -> worse case
What considerations should be made for specimen collection and handling of
creatinine and urine creatinine
testing?
Generally, for serum creatinine and blood urea nitrogen (BUN) levels, no additional patient preparation is required, and a random blood sample suffices.
However, the effect of recent high protein ingestion may increase serum creatinine and urea levels to a significant extent.
Hydration status can have a considerable impact on BUN measurement.
For timed urine collections such as the 24-hour urine creatinine clearance, it is essential that urine be collected accurately over the required period as under or over collection will affect final results. Hence, a 5 to 8-hour timed collection is preferable to a 24-hour collection.
The collection of midstream urine for urine analysis is required as this sample is less likely to be contaminated by epithelial cells and commensal bacteria.
- What is considered non-protein nitrogen (NPN), what analytes are measured under this term
catabolites of protein and nucleic acid metabolism, including urea, ammonia, creatinine, creatine, and uric acid, aas
- What are two preanalytical sources of error that need to be avoided in order
to provide accurate creatinine values?
Preanalytical issues such as high-protein intake and increased muscle bulk may lead to elevated creatinine levels, but it is not representative of the actual renal function in an individual.
Likewise, serum creatinine as a marker of renal function is often unreliable in those with decreased muscle bulk such as the elderly, amputees, and individuals affected by muscular dystrophy.
Serum, plasma, and urine may be measured enzymatically. Fluoride and ammonium
heparin should not be used as anticoagulants in enzymatic methods
Urine: used preservative if not assessed immediately
- What are the key reagents that react with urea, forming a measurable product?
water and enzyme urease? (for enzymatic method)
What are two preanalytical sources of error that need to be avoided in order
to provide accurate urea values?
Generally, for serum creatinine and blood urea nitrogen (BUN) levels, no additional patient preparation is required, and a random blood sample suffices. However, the effect of recent high protein ingestion may increase serum creatinine and urea levels to a significant extent. Also, hydration status can have a considerable impact on BUN measurement.
