Results of a multicenter evaluation of automated assays for measurement of apolipoproteins (apo) A-I and B with the Paramax analytical system are reported. Apo A-I and apo B response surface models were used to optimize concentrations of critical assay variables. Overall imprecision for apo A-I controls at concentrations of 1.01-1.61 g/L was 3.7-6.6%; overall imprecision for apo B controls at 1.00-1.61 g/L was 2.8-6.9%. There was no interference in apo A-I measurements. Albumin concentrations > 59 g/L resulted in a negative interference, and collection in sodium heparin caused a positive interference in apo B results. Apo A-I and apo B assays demonstrated acceptable agreement with comparative methods, although the Paramax apo B assays had a negative bias with respect to comparison methods. In 116 healthy individuals, serum apo A-I ranged from 0.97 to 2.05 g/L and serum apo B ranged from 0.51 to 1.32 g/L.
The accurate measurement of low serum creatinine levels is necessary for estimating clinically useful creatinine clearances in the pediatric population. This study compares two routine clinical methods: the kinetic Jaffé with the newer Kodak enzymatic method against our reference method, high-pressure liquid chromatography, for the measurement of serum and urine creatinine levels in neonates. One hundred and twenty-five serum and 59 urine creatinines and 56 absolute creatinine clearances were measured in neonates ranging from 23 to 46 weeks (mean 32 weeks) post-conceptional age and weighing 480-4398 g (mean 1650 g). Urine creatinine levels, and serum creatinine levels greater than 0.8 mg/dl were equivalent for both clinical methods. However, the enzymatic method was much more accurate (P less than 0.001) than the kinetic Jaffé method for serum creatinine measurements of less than or equal to 0.8 mg/dl. We conclude that the enzymatic methodology is a better clinical choice for the accurate measurement of serum creatinine levels when using these values for the determination of neonatal renal function.
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