Kidney Function Testing Overview
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Questions and Answers

What is the relationship between plasma concentration and clearance for substances in renal function?

  • There is no significant relationship.
  • They fluctuate independently.
  • They are directly proportional.
  • They are inversely proportional. (correct)

    • In advanced renal failure, urea clearance approaches which value in relation to GFR?

  • Unity with GFR (correct)
  • Twice the GFR
  • Infinity
  • Zero

    • What happens to the fraction of urea reabsorbed as renal function declines?

  • It remains constant.
  • It increases progressively.
  • It decreases progressively. (correct)
  • It fluctuates randomly.

    • What is an indirect estimate of GFR based on tubular damage?

    <p>Urea concentration in urine</p> Signup and view all the answers

    Which method for urea measurement converts urea to ammonia and carbon dioxide?

    <p>Hydrolysis by Ureases</p> Signup and view all the answers

    What indicates that tubular secretion of creatinine is occurring at increased levels?

    <p>Higher plasma creatinine concentration.</p> Signup and view all the answers

    What is a key advantage of measuring Cystatin C?

    <p>Assess GFR among pediatric and elderly patients.</p> Signup and view all the answers

    Which of the following patients may require IVGTT?

    <p>Patients with altered gastric physiology or GI disorders</p> Signup and view all the answers

    What could be a sign of damage to renal tubules based on the urea metabolic pathway?

    <p>Increase in urea concentrations in urine.</p> Signup and view all the answers

    What method is involved in the Hagedorn Jensen/Ferric Reduction principle?

    <p>Reduction of yellow ferricyanide to colorless ferrocyanide</p> Signup and view all the answers

    Which of the following methods is not recommended for routine use?

    <p>HPLC</p> Signup and view all the answers

    What is the life span of a red blood cell (RBC)?

    <p>120 days</p> Signup and view all the answers

    Which reagent is used in the Ortho-Toluidine method?

    <p>Glacial acetic acid</p> Signup and view all the answers

    What occurs during the condensation method in glucose analysis?

    <p>Color develops by protein precipitation</p> Signup and view all the answers

    What is a major interfering substance in the Ortho-Toluidine method?

    <p>Mannose</p> Signup and view all the answers

    Which of the following methods is a sensitive indicator of cellular metabolic activity?

    <p>MTT method</p> Signup and view all the answers

    What is the primary purpose of the colorimetric method described?

    <p>To determine the concentration of TAG</p> Signup and view all the answers

    What colored product is produced through the colorimetric method for TAG analysis?

    <p>Blue</p> Signup and view all the answers

    Which method produces yellow fluorescence as an end product?

    <p>Fluorometric method</p> Signup and view all the answers

    What is the major interference when using enzymatic methods for TAG analysis?

    <p>Endogenous glycerol</p> Signup and view all the answers

    What is the preferred choice for TAG analysis due to its accuracy and reliability?

    <p>Enzymatic methods</p> Signup and view all the answers

    Which enzymes are involved in the glycerol kinase method for TAG measurement?

    <p>Glycerol kinase and lipase</p> Signup and view all the answers

    What does the new CDC reference method utilize for TAG analysis?

    <p>Gas chromatography/Mass Spectrometry (GC-MS)</p> Signup and view all the answers

    What is the main advantage of using enzymatic methods directly in plasma or serum?

    <p>Higher measurement accuracy</p> Signup and view all the answers

    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?

    <p>High BUN and high creatinine</p> Signup and view all the answers

    Which condition is characterized by the failure of kidneys to eliminate waste products of metabolism and can result in uremic frost?

    <p>Uremia</p> Signup and view all the answers

    What is the primary cause of high plasma uric acid in newborns?

    <p>Transient physiological phenomena</p> Signup and view all the answers

    Why should potassium oxalate not be used as an anticoagulant when measuring uric acid?

    <p>It interferes with ascorbic acid measurements</p> Signup and view all the answers

    What primarily determines the osmolality of urine?

    <p>Urea</p> Signup and view all the answers

    In chemical methods for measuring uric acid, what is the lag phase?

    <p>Incubation to inactivate non-uric acid reactants</p> Signup and view all the answers

    Which of the following laboratory test results would likely suggest Fanconi's syndrome?

    <p>Increased amino acids in urine</p> Signup and view all the answers

    Which of the following compounds primarily contributes to serum osmolality?

    <p>Sodium and chloride</p> Signup and view all the answers

    What does the Para-Amino Hippurate Test measure?

    <p>The renal plasma flow</p> Signup and view all the answers

    What is the reference value for renal plasma flow during the Para-Amino Hippurate Test?

    <p>600-700 mL/minute</p> Signup and view all the answers

    What does an SG of 1.010 indicate?

    <p>Severe loss of concentrating ability</p> Signup and view all the answers

    Which of the following tests can detect renal damage that is not yet severe?

    <p>Phenolsulfonthalein Dye Test</p> Signup and view all the answers

    Which method is considered a direct method for measuring osmolality?

    <p>Freezing point osmometry</p> Signup and view all the answers

    What is the significance of hypersthenuria in urine analysis?

    <p>Suggests dehydration or high solute load</p> Signup and view all the answers

    To calculate serum osmolality using glucose or urea, what must be considered?

    <p>Convert from mg to molar units</p> Signup and view all the answers

    What does a reference serum osmolality of 275-295 mOsm/kg represent?

    <p>Normal plasma osmolality levels</p> Signup and view all the answers

    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

    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!

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