Objectives Mention the normal serum creatinine level Enumerate the methods of estimation of creatinine Discuss the clinical significance for increased and decreased serum creatinine What is Creatinine? Creatinine (from the Greek ''kreas'', flesh) is a break-down product of creatine phosphate in muscle, and is usually produced at a fairly constant rate by the body (depending on muscle mass). Creatinine is a metabolic product of creatine and phosphocreatine, which are both found almost exclusively in muscle. Thus, creatinine production is proportional to muscle mass and varies little from day to day. However, production can change over periods of time if there is changes in muscle mass. Age-and gender-associated differences in creatinine production are also largely attributable to differences in muscle mass. Although diet ordinarily accounts for only a relatively small proportion of overall creatinine excretion, it is another source of variability in serum creatinine levels. Creatine from ingested meat is converted to creatinine and can be source of up to 30% of total creatinine excretion. Thus, variability in meat intake can also contribute to variability in serum creatinine levels. The conversion of creatine to creatinine can occur with cooking. Since creatinine is readily absorbed from the gastrointestinal tract, ingesting cooked meat can lead to a rapid increase in serum creatinine levels. Serum creatinine test used to diagnose impaired renal function. It is more specific and sensitive indicator of kidney disease than BUN, although in chronic renal disease, both BUN and creatinine are ordered to evaluate renal problems, because BUN/creatinine ratio provides more information. A- Increased Serum Creatinine: – Impaired renal function. – Chronic nephritis. – Muscle disease B- Decreased Serum Creatinine – Decreased muscle mass. – Advanced and severe liver disease. – Inadequate dietary protein. Determination of serum Creatinine Types of Samples: Serum or plasma with heparin and urine. Serum or plasma samples are stable for 24 hours at 2-8o C. To assay urinary creatinine, dilute the sample 1/20 in deionized water. Multiply the final result by 20. Requirements Requirements: Automatic pipettes Tips Cuvettes Spectrophotometer Reagent Specimen: Serum or plasma Working Reagent Mix equal parts of each reagent (A and B) prior to assay. The concentration in the working reagent are: Picric acid 55 mM Sodium carbonate 50 mM NaOH 0.40 M Preservative and stabilizers Preparation of Cuvettes Blank (only Reagent) Standard (Reagent+ St. sample) Sample (Reagent+Serum) At alkaline pH values, creatinine reacts with picric acid to produce a coloured compound, creatinine alkaline picrate, which is photometrically measured. Reagents Creatinine Standard (μl) Serum Sample (μl) Creatinine Reagent (ml) 1 2 3 200 - - - 200 - 2.0 2.0 2.0 Mix well. Read the absorbance at 546 nm (510 546). Zero the spectrophotometer against blank. Read the absorbance after 20 second (A1) and after 80 second (A2). Calculate the absorbance change (Δ A). Calculations: For Serum: Serum Creatinine (mg/dl) = Absorbance of the sample (A2 - A1 ) X Con. Of std Absorbance of the standard ( A2 - A1 ) Serum creatinine (mg/dl) Males Females 0.6 - 1.1 0.5 – 0.9