Determination of pseudocholinesterase phenotype with the Kodak Ektachem DT-60

✍ Scribed by L. Dallaire; M. Guitard

• Publisher: Elsevier Science
• Year: 1993
• Tongue: English
• Weight: 100 KB
• Volume: 26
• Category: Article
• ISSN: 0009-9120
• DOI: 10.1016/0009-9120(93)90094-m

✦ Synopsis

Due to the limited range (0-1.8 mmol/L) of serum creatinine, urine creatinine has traditionally been determined by pre-diluting the sample, performing a serum assay, and multiplying the result by the dilution factor. We modified the kinetic Jaff6 procedure for direct measurement of urine creatinine on the Hitachi 717. We determined assay linearity, precision, interferences and clinical equivalency.

Using kinetic measurement and dual wavelength (570/505 rim), the method minimizes creatinine interferences. Assay reagents are 200 mmol/L sodium hydroxide and 28.2 mmol/L picric acid with volumes of 350 laL and 70 I~L, respectively. The final concentrations of sodium hydroxide and picric acid are 165 mmol/L and 4.7 mmol/L, respectively. Sample volume is 3 pL. The assay is linear from 0.9 to 17.7 mmol/L. Automatic instrument dilution can extend this to 53.1 mmol/L. Common urine preservatives at 10 times recommended concentrations showed less than 3% negative interference. Elevated levels of L-ascorbic acid, urea, glucose and albumin did not interfere. Cefazolin at concentrations 3 and 10 times therapeutic levels falsely elevated creatinine 2% and 13%, respectively. Imprecision studies exhibited within-run CV of 1.1% at 1.8 mmol/L and 1.2% at 12.1 mmol/L; between-run CV of 3.5% at 1.8 mmol/L and 3.2% at 5.9 mmol/L. Two split sample studies with an in-house pre-dilution assay using samples ranging from 1.0-23.0 mmol/L and CAP proficiency samples, had slopes of 1.02 (r=0.997, n=78) and 0.993 (r=0.999, n= 14), respectively.

We conclude that this method is acceptable for measuring urine creatinine. Interferences will be similar to other kinetic Jaffd methods, but eliminating the dilution step saves time and improves precision.