Core Area One: Renal

1
Core Area One Renal

• Group A
• Analgesic Nephropathy
• The Jaffe Method
• Enzymatic Assays

2
Analgesic Nephropathy

• A chronic kidney disease that gradually leads to
  end-stage renal disease (ESRD) and the need for
  permanent dialysis or a kidney transplant to
  restore renal function.
• Its likely cause is the habitual use of compound
  analgesics such as acetaminophen and aspirin.
• Predominates in women peak incidence at age 50-55
  years.
• Symptoms usually develop after a cumulative
  analgesic dose of 2-3 Kg.

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Manifestations of Analgesic Nephropathy

• Acute renal failure sudden loss of the ability
  of the kidneys to remove wastes, concentrate
  urine and conserve electrolytes
• -Urinalysis may be normal.
• -Serum Cr may increase.
• -Blood Urea Nitrogen (BUN) may increase.
• -Serum K may increase.
• - Metabolic acidosis may develop.

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Manifestations of Analgesic Nephropathy

• Chronic Renal failure Gradual and progressive
  loss of the ability of the kidneys to excrete
  wastes, concentrate urine and conserve
  electrolytes
• -Urinalysis may show protein or other
  abnormalities.
• -Serum Cr progressively increases.
• -BUN progressively increases.
• - Serum K levels increase.
• -Metabolic acidosis develops.

5
Manifestations of Analgesic Nephropathy

• Interstitial Nephritis Inflammation of the
  tubules and the spaces between the tubules and
  the glomeruli
• -Small amounts of protein and sometimes
  red blood cells.
• -WBCs, WBC casts, RBCs may appear in urine.
• -Urine pH raised and metabolic acidosis.
• -BUN and serum Cr increase.

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Manifestations of Analgesic Neohropathy

• Renal papillary necrosis.
• Urinary tract infections.
• Hypertension.

7
The Jaffe Method Principle of Operation

• Jaffe reaction
• CreatininePicrate----gt Complex
• (Alkaline conditions)
• Complex is red-orange, easily detected and
  quantified.

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The Jaffe MethodPositive Interference

• Positive interference in normal subjects of up to
  20 caused by non-creatinine chromogens
• -glucose, ascorbate, uric acid etc.
  that slowly reduce alkaline picrate.
• -Acetoacetate, pyruvate and other
  ketoacids and proteins that form colored
  complexes with alkaline picrate.
• This leads to the GFR being underestimated.
  However these interferences are accounted for in
  normal subjects BUT become significant in
  diseased individuals with ketoacidosis and
  cephalosporin treatment.

9
The Jaffe Method Negative Interference

• Caused by high bilirubin levels as well as other
  compounds in the serum of jaundiced patients.The
  mechanism of action is not fully understood.
• GFR is overestimated as the measured creatinine
  concentration is reduced.

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The Kinetic Jaffe Method

• Rate of color development of creatinine is
  different to that of non-creatinine chromogens.
• Creatinine can now be seperated from interfering
  substances as reactions are rate-dependent.
• Positive interference is significantly reduced
  however it is not eliminated. (This reduces the
  reference range for this method by 20 cf the
  standard Jaffe Method which is a problem when
  comparing results from different labs)
• Negative interference is still significant.

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Enzymatic Assays Principle of Operation

• A series of sequential enzyme mediated steps.
• Initial step degradation of creatinine.
• Final step Enzymatic production of a
  quantifiable product.
• Can be a one step assay.

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Enzymatic Assays Principle of Operation

• A Few Examples
• Cratinine PAP Method
• Creatinine----gtCreatine (Creatininase)
• Creatine----gtUreaSarcosine (Creatinase)
• Sarcosine----gtFormaldehydeGlycine Hydrogen
  Peroxide (Sarcosine Oxidase)
• Hydrogen PeroxideIndicator----gtRed
  Benzoquinone-imine dye (A substance that absorbs
  at a maximum ? of 510 nm)

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Enzymatic Assays Principle of Operation

• The Ektachem Method
• Creatinine----gtN-methyldantoin Ammonia
• (Ammonia is quantified via a reaction with
  Bromophenol)

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Enzymatic Assays Advantages

• Precise
• Accurate
• Practical
• Easily adaptable
• Use a small sample size
• Rapid
• Show Clinical specificity

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Enzymatic Assays Disadvantages

• Expensive
• Interference
• Variation in reference ranges
• Imprecise at lower serum creatinine concentrations

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Jaffe Method Comparison to the Enzymatic Assay
Method

• Relative Accuracy
• Same accuracy in normal individuals
• More accurate in diseased individuals
• allowing -No no interference from
  increased glucose levels
• -No interference from
  increased ketone bodies
• -No interference from
  cephalosporins
• -Reduced interference
  from increased bilirubin levels

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Jaffe Method comparison to the Enzymatic Assay
Method

• (Applies to the PAP method, as other assays
  differ in level of intrference or type of
  interfering substance)

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Clinical Implications of Discrepancies Between
the two Protocols

• The enzyme assay method, due to no or reduced
  interference, becomes a more diagnostic
  laboratory tool for the measurement of serum
  creatinine levels in patients with diabetes
  mellitus, neonates, and patients receiving
  cephalosporins.

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Conclusion

• The Jaffe Method has both positive and negative
  interference issues especially problematic in
  diseased patients suffering from ketoacidodsis,
  jaundice or undergoing cephalosporin treatment.
• The kinetic Jaffe Method overcomes the positive
  interference issues but not the negative
  interference issues and cant be used in
  jaundiced patients..
• The Enzyme Assay Method overcomes both the
  positive and the negative interference issues and
  is a better diagnostic tool to use in diseased
  patients.
• Standardization is required for reference ranges
  of the different assays.