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Questions and Answers
What is the relationship between plasma concentration and clearance for substances in renal function?
In advanced renal failure, urea clearance approaches which value in relation to GFR?
What happens to the fraction of urea reabsorbed as renal function declines?
What is an indirect estimate of GFR based on tubular damage?
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Which method for urea measurement converts urea to ammonia and carbon dioxide?
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What indicates that tubular secretion of creatinine is occurring at increased levels?
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What is a key advantage of measuring Cystatin C?
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Which of the following patients may require IVGTT?
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What could be a sign of damage to renal tubules based on the urea metabolic pathway?
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What method is involved in the Hagedorn Jensen/Ferric Reduction principle?
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Which of the following methods is not recommended for routine use?
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What is the life span of a red blood cell (RBC)?
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Which reagent is used in the Ortho-Toluidine method?
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What occurs during the condensation method in glucose analysis?
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What is a major interfering substance in the Ortho-Toluidine method?
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Which of the following methods is a sensitive indicator of cellular metabolic activity?
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What is the primary purpose of the colorimetric method described?
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What colored product is produced through the colorimetric method for TAG analysis?
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Which method produces yellow fluorescence as an end product?
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What is the major interference when using enzymatic methods for TAG analysis?
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What is the preferred choice for TAG analysis due to its accuracy and reliability?
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Which enzymes are involved in the glycerol kinase method for TAG measurement?
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What does the new CDC reference method utilize for TAG analysis?
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What is the main advantage of using enzymatic methods directly in plasma or serum?
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What would be expected in the lab results of a patient with severe renal dysfunction indicated by a BUN greater than 100 mg/dL and a creatinine level of 20?
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Which condition is characterized by the failure of kidneys to eliminate waste products of metabolism and can result in uremic frost?
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What is the primary cause of high plasma uric acid in newborns?
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Why should potassium oxalate not be used as an anticoagulant when measuring uric acid?
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What primarily determines the osmolality of urine?
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In chemical methods for measuring uric acid, what is the lag phase?
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Which of the following laboratory test results would likely suggest Fanconi's syndrome?
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Which of the following compounds primarily contributes to serum osmolality?
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What does the Para-Amino Hippurate Test measure?
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What is the reference value for renal plasma flow during the Para-Amino Hippurate Test?
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What does an SG of 1.010 indicate?
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Which of the following tests can detect renal damage that is not yet severe?
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Which method is considered a direct method for measuring osmolality?
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What is the significance of hypersthenuria in urine analysis?
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To calculate serum osmolality using glucose or urea, what must be considered?
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What does a reference serum osmolality of 275-295 mOsm/kg represent?
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Study Notes
Non-protein Nitrogenous (NPN) Substances
-
Urea
- Concentration and clearance are inversely proportional
- Increased concentration indicates kidney disease progression or response to therapy
- Good predictor of GFR in advanced renal failure
- Tubular reabsorption decreases as renal function declines
Cystatin C
- Produced constantly by all nucleated cells
- Freely filtered at glomerulus
- Not secreted by renal tubules but reabsorbed
- Serum levels indicative of GFR
Blood Uric Acid
- Fasting not required for routine testing, but preferred for diagnostic purposes
- May be high in newborns but eventually decreases
- Potassium oxalate anticoagulant should not be used because it interferes with the assay
Tests for Measuring Tubular Function
-
Para-Amino Hippurate Test (Diodrast Test)
- Measures renal blood flow
- Requires clearance of the dye
- Reference value: 600-700mL/minute
-
Phenolsulfonthalein Dye Test
- Measures excretion of dye in proportion to renal tubular mass
- 6mg PSP administered intravenously
- Reference value: 1200mL blood flow/ minute
Concentration Test
- Reflects function of collecting tubules and loops of Henle
- Detects renal damage before elevated plasma urea and creatinine levels
- Specimen: first morning urine
Specific Gravity (SG)
- Simplest test of renal concentrating ability
- SG fixation at 1.010 indicates severe loss of concentrating ability
- Reference value: 1.005-1.030
- Why can't we consider 1.000 a normal SG of urine?
Uremia
- Kidneys fail to eliminate waste products of metabolism
- Characterized by: anemia, uremic frost, generalized edema, foul breath and sweat odor resembling urine
Osmolality
- Serum osmolality is primarily due to sodium and chloride
- urine osmolality is primarily due to urea
- Normal ratio of urine:serum osmolality is 1:1
- Reference values:
- Serum: 275-295 mOsm/kg
- Urine: 300-900 mOsm/kg
- Direct Method: Freezing point osmometry
- Vapor pressure Osmometry (Seebeck Effect) : Increase in osmolality decreases freezing point and vapor pressure
- Indirect Method: Formula for Computing Serum Osmolality: To use glucose or urea in osmolality, calculations must be converted to molar units
Conversion Factors
- BUN
- Conventional unit: 8-23 mg/dL
- SI unit: 2.9-8.2 mmol/L
- Conversion factor: 0.357
- Serum or Plasma Creatinine
- Adult:
- Conventional unit: 0.6-1.2 mg/dL
- SI unit: 27-53 umol/L
- Conversion factor: 88.40
- Adult:
Post Renal
- Urinary tract obstruction
- Urea is higher than creatinine due to back-diffusion of urea into circulation
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Description
This quiz covers key concepts related to non-protein nitrogenous (NPN) substances, including urea, cystatin C, and blood uric acid, as well as various tests for measuring tubular function. It highlights important markers for assessing kidney health and function. Prepare to test your knowledge on renal diagnostics!