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R S Schifreen

Publications and source records attributed to R S Schifreen.

12 recordsLinked to original sources
PubMed1988

Development and performance of a fully automated method for assay of C-reactive protein in the aca discrete clinical analyzer.

A quantitative immunoassay for C-reactive protein (CRP) has been developed for use in the Du Pont aca discrete clinical analyzer. Particle-enhanced turbidimetric immunoassay (PE-TIA) technology is used. The method has a CV of less than 10% in the range 2 to 120 mg/L. Neither hemolyzed samples (Hb less than 5 g/L), icteric samples (total bilirubin less than 300 mg/L), lipemic samples (triglyceride less than 15 g/L), nor some commonly used drugs interfere. Dithioerythritol is used to eliminate interference from rheumatoid factor. Good correlation was seen when the Du Pont CRP method was compared with the Beckman ICS, Syva EMIT, TDx, and Behring methods for CRP. The normal reference interval is 0 to 9 mg/L. The method, which is fully automated, is fast, requires only a few microliters of serum, and is well suited to emergency-room requirements.

Autoanalysis↗
PubMed1987

Prototype quantitative assay for fibrinogen/fibrin degradation products. Clinical evaluation.

A new quantitative assay for fibrinogen/fibrin degradation products (FDPs) was clinically evaluated in 123 tertiary-care patients for whom the standard semiquantitative FDP assay had previously been ordered. On the basis of a comprehensive chart review, 24 patients were categorized as having disseminated intravascular coagulation (DIC), 84 were considered not to have had DIC, ten had fibrinolysis (nine of ten streptokinase induced), and five had a complicated coagulopathy whose exact nature could not be determined. The quantitative and semiquantitative FDP values were significantly correlated. However, the FDP level indicative of DIC was lower by the quantitative assay than by the semiquantitative assay, approximately 18 mg/L vs 40 mg/L, respectively. The advantages of the quantitative over the semiquantitative assay included improved precision and ability to closely monitor changes in the severity of the coagulopathy.

Disseminated Intravascular Coagulation↗
PubMed1986

Controlling the cost of quality control.

In the present era of expanding technology coexisting with economic constraint, appropriate quality control criteria to monitor laboratory performance must take into consideration not only analytic precision and medical utility, but also cost effectiveness. In this review, the effect of existing criteria on the clinical laboratory, the regulator, and the vendor is explored. Factors that contribute to excessive quality control cost are delineated. Strategies for developing a cost-effective quality control program are proposed.

Costs and Cost Analysis↗
PubMed1985

A quantitative automated immunoassay for fibrinogen/fibrin degradation products.

We describe a prototype quantitative automated assay for fibrin and fibrinogen degradation products, a particle-enhanced turbidimetric inhibition immunoassay (PETINIA) in the Du Pont aca discrete clinical analyzer. This assay involves a latex particle reagent with covalently bound fibrinogen and a polyclonal antiserum raised in rabbits against human fibrinogen. A special secondary sample-collection tube quantitatively removes fibrinogen from citrated plasma and inhibits further fibrinolysis, independent of heparin concentration. The assay range is 0-100 mg/L, in fibrinogen equivalents. The CV for the assay is less than 10% when performed with the aca. Nonclottable fibrin and fibrinogen fragments are measured by the assay, the greatest sensitivity being directed at the E domain of the fibrinogen molecule. We illustrate with case studies the potential of this assay for providing clinical information not obtainable with currently available qualitative and semi-quantitative assays.

Adult↗
PubMed1981

Spectrophotometric and liquid-chromatographic studies of thymolphthalein monophosphate. Specifications for high-quality substrate for the measurement of prostatic acid phosphatase activity.

Fourteen lots of thymolphthalein monophosphate (TMP), disodium salt, obtained from 10 commercial suppliers were compared spectrophotometrically at 445 and 595 nm, liquid-chromatographically with monitoring at 254 nm, and enzymically by measurements of activity of prostatic acid phosphatase in human serum. Eight lots were classified as "unacceptable," six as "acceptable." Spectrophotometric testing revealed four lots with excessive thymolphthalein and three lots with grossly deficient amounts of TMP. In general, the chromatographic results paralleled those obtained by spectrophotometry, and both results correlated well with enzymic activity. Changing water content in this hygroscopic salt was a major problem, which resulted in great uncertainty as to the formula weight and therefore as to the moles of TMP actually taken. From these studies, specifications for high-quality TMP were determined. The critical importance of simultaneous enzymic activity measurements in comparisons with other "acceptable" lots in defining an adequate TMP substrate is stressed. Use of these specifications for selecting TMP for acid phosphatase activity measurements should improve intra- and inter-laboratory analytical performance.

Acid Phosphatase↗
PubMed1980

Accuracy, precision, and stability in measurement of hemoglobin A1C by "high-performance" cation-exchange chromatography.

We present a "high-performance" liquid-chromatographic method for determination of HbA1c with use of a carboxylate cation-exchange column, ethanolic mobile phases, and a hemolysate-storage reagent that stabilizes a sample for up to five weeks at 4 degrees C. Temperature control and the addition of ethanol to the phosphate step-gradient increase precision by stabilizing peak shape and column activity. Lengthy equilibration of the column between samples is not necessary, because the pKa of the cation-exchange resin is decreased from 6.10 in aqueous media to 5.59 in ethanol/water (5/95 by vol) at 25 degrees C. We identified interfering heme compounds, distinct from HbA1d or HbA1e, that elute with the glycosylated hemoglobins and developed a method of correcting for their presence. The day-to-day coefficient of variation was 3.5%, and the reference interval for a mixed group of 20 healthy adults between the ages of 20 and 56 was 3.2--5.2% HbA1c.

Chromatography, High Pressure Liquid↗
PubMed1979

Effects of wavelength error and spectral band width on measurement of alkaline phosphatase activity.

We re-examined the effects of wavelength error and spectral band width on the measurement of alkaline phosphatase activity. The methods we studied is relatively insensitive to these two factors, a conclusion we base on both experimental results and theoretical analysis. These findings are in conflict with a recently published report [Lott et al., Clin. Chem. 24, 938 (1978)], and we suggest a possible explanation for this.

Alkaline Phosphatase↗