Lecture 5-8 Flashcards
(29 cards)
GFR
What is it
decreased rate means?
how its measured
-measures volume of filtrate formed per minute
-decreased GFR= renal impairment
measured by creatinine clearance
Urea
where is it produced
preanalytical considerations
produced in the liver as nitrogenous waste product on protein catabolism
for blood urea use serum or plasma (LiHep)
-avoid fluoride and critate since they inhibit urease
for urine urea - preserve 24 hours with thymol and put in fridge to avoid bacterial degradation
Increased urea causes
pre renal
renal
post renal
decreased urea
Increased urea causes AZOTEMIA
-pre renal - hypovalemia, cardiac impairment , shock
-renal- glomerunep, tubular necrosis, diabetic nephropathy
-post renal-obstruction like renal calculi or tumors
decreased urea - in severe liver disease where ammonia conversion to urea is impaired
how to analyze urea and sources of error
Enzymatic method
-urease converts urea to ammonia
nadh/nad enzymatic reaction (670nm abs)
-ion selective electrodes for NH4+ detection
-vitros
sources of error
ammonia contamination (falsely increased) , improper storage causing urea degradation
ammonia in urine has to be removed first
-urease inhibited by Hg
-use clean glassware
why is creatinine of clinical importance
- more specific marker of renal function than urea but less sensitive for early dysfunction
What is the Jaffe reaction
measurement of creatinine
-measures endpoint reaction
-lacks specificity
-measures creatinine picrate complex at 510 nm
-needs alkaline pH
-constant temp ; increase temp increase reaction rate of non creatinine chromogen
-time to be constant ; increase in time increase reaction rate of non creatinine chromogen
sources of error in the Jaffe reaction
Hemolysis – falsely increases result.
Icteremia – falsely decreases result.
Lipemia – falsely decreases result.
Ammonium heparin – falsely increases result.
Non-specific chromogens such as protein, glucose, acetoacetate, ascorbic acid, cephalosporins, ammonium – falsely increase results
What type of enzymatic reaction is used for creatinie
coupled enzymatic reaction
-measuring reflectance at 2 points at 670nm
-uses creatinine amidohydrolase
-measures colored end product
Creatinine Clearance is calculated using
o : Urine creatine
o : Urine flw rate (mL/s)
o : Serum creatinine
o : Body surface area (m)
o Assess GFR and renal function.
o Correct for body size using the BSA factor.
Hyperuricemia: causes
associated conditions
Overproduction: High purine diet, genetic disorders
Treat with Salicylates, Allopurinol, diuretics,
Underexcretion: Renal impairment, lactic acidosis
▪ Gout: Diagnosed by identifying urate crystals in synovial flid.
▪ Uric acid nephrolithiasis
Hypouricemia seen in
Fanconi syndrome or with medications such as allopurinol.
how to measure uric acid with coupled enzymatic reactions
- Uricase catalyzes uric acid to allantoin to produce a colored dye , reflectance measured at 670nm.
sources of error
high bilirubin causes falsely decreased UA
hemolysis can falsely elevate creatinine or UA
Specimen type for uric acid
serum, hep plasma, urine
- remove plasma from cells asap
crystals in fluid are diagnostic
Types of samples to collect for urine
o Random: Convenient but subject to variability.
o First morning: Preferred for concentration and stability.
o Clean-catch midstream: Minimizes contamination
Leakproof , clean, sterile
put in fridge to reduce bacterial growth , can precipitate crystals
- chemical preservatives cannot interfere will tests
What does a turbid urine suggest
presence of cells, crystals, or bacteria.
Glucose and ketones in urine suggest
- Glucose: Indicates hyperglycemia (e.g., DM).
- Ketones: Elevated in Type 1 DM, starvation, or malabsorption
What does protein in urine suggest
o Most indicative of renal disease.
o False positives: Highly alkaline urine.
o Confirmatory Test: Sulfosalicylic acid (SSA).
What does pH , blood, Leukocyte Esterase and Nitrite in urine suggest
.
* pH: Reflcts acid-base balance; range 4.5-8.0.
- Blood: Detects hematuria (intact RBCs) or hemoglobinuria (free hemoglobin).
- Leukocyte Esterase: Detects WBCs, indicating inflammation or infection.
- Nitrites: Suggests bacterial UTI due to nitrate-reducing organisms.
What does Bilirubin , and specific gravity in urine suggest
- Bilirubin: Indicates liver dysfunction or bile duct obstruction.
- Specific Gravity:
o Normal Range: 1.003-1.035.
o High SG: Dehydration or presence of glucose/protein.
o Low SG: Diabetes insipidus.
What is the instrument method to reading the urine dipstick
Reflectance spectrophotometry improves precision in reagent strip readings.
What are RBCS, wbcs, and epithelial cells suggestive of
▪ RBCs: Hematuria from trauma, malignancy, or glomerulonephritis
▪ WBCs: Indicative of UTI or pyelonephritis.
▪ Epithelial Cells: Squamous (contaminants), transitional (catheterized), renal tubular (acute tubular necrosis).
What type of casts would you see
▪ Hyaline: Normal in small numbers; increased with dehydration.
▪ RBC Casts: Pathologic, indicative of glomerulonephritis.
▪ WBC Casts: Seen in pyelonephritis.
▪ Waxy Casts: Advanced renal failure.
▪ Fatty Casts: Nephrotic syndrome, confirmed with polarizing microscopy.
How are bacteria graded
and what type of yeast would you see
▪ Bacteria: Graded as 1+, 2+, etc.; differentiate contamination from infection.
▪ Yeast: Seen in diabetes or immunosuppression.
▪ Trichomonas: Flagellated protozoa indicating infection
what types of normal crystals would you see
▪ Acidic: Uric acid, calcium oxalate.
▪ Alkaline: Triple phosphate, calcium carbonate
