Group A Analgesic Nephropathy The Jaffe Method Enzymatic Assays Core Area One: Renal Group A Analgesic Nephropathy The Jaffe Method Enzymatic Assays

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.

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.

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.

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.

Manifestations of Analgesic Neohropathy Renal papillary necrosis. Urinary tract infections. Hypertension.

The Jaffe Method: Principle of Operation Jaffe reaction: Creatinine+Picrate----> Complex (Alkaline conditions) Complex is red-orange, easily detected and quantified.

The Jaffe Method:Positive 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.

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.

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.

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.

Enzymatic Assays: Principle of Operation A Few Examples: Cratinine PAP Method: Creatinine---->Creatine (Creatininase) Creatine---->Urea+Sarcosine (Creatinase) Sarcosine---->Formaldehyde+Glycine +Hydrogen Peroxide (Sarcosine Oxidase) Hydrogen Peroxide+Indicator---->Red Benzoquinone-imine dye (A substance that absorbs at a maximum  of 510 nm)

Enzymatic Assays: Principle of Operation The Ektachem Method: Creatinine---->N-methyldantoin +Ammonia (Ammonia is quantified via a reaction with Bromophenol)

Enzymatic Assays: Advantages Precise Accurate Practical Easily adaptable Use a small sample size Rapid Show Clinical specificity

Enzymatic Assays: Disadvantages Expensive Interference Variation in reference ranges Imprecise at lower serum creatinine concentrations

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

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)

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.

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 can’t 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.