engleski

COMPARISON OF DIFFERENT SPECIMENS FOR FT4 AND FT3 VERIFICATION: COMMERCIAL CONTROL VS. PATIENT SAMPLE

Background: Precision is the most important component of the quality of laboratory results and precision check is one of the requirements for quality control and accreditation of laboratory. Guidelines for method verification recommend the use of control samples, calibrators or previously analyzed patient samples for precision check. The aim of this study was to compare parameters of precision for free thyroxine (FT4) and free triiodothyronine (FT3) obtained by analyzing internal quality control samples and pool of previously analyzed patient specimens on Unicel DxI600 (Beckman Coulter, Tokyo, Japan). Materials and Methods: The methods verification was done using control samples BioRad Lypocheck Immunoassay Plus Control (Biorad Laboratories, Marnes-la- Coquette, France) and pool of previously analyzed patient serums, both with high and low levels of analyzed hormones. Samples were tested 10 times in the series (within-run imprecision) and every day in duplicate during 10 days (between-run imprecision). The results are expressed as coefficients of variations (CV) and compared with values provided by manufacturer and by Westgard desirable specifications for imprecision. CV was calculated using Microsoft office Excel 2007 software while the comparison of CV values between control samples and patient samples was performed using MedCalc 12.4.0.0. software (MedCalc, Mariakerke, Belgium). P < 0.05 was set as level of significance. Results: The results of within- run imprecision and between-run imprecision analyzed by commercial control samples and by patient samples for both tests were in accordance with specifications provided by manufacturer but not within desirable range according to Westgard. We did not found statistically significant difference in CV values between control samples and patient specimens (t-test: P = 0.827). Conclusions: Patient samples and commercial control samples are equally suitable for imprecision testing of FT3 and FT4. Although simpler and safer procedure is provided by using control materials, using of patient samples is a cheaper way for precision checking.

within-run imprecision, between-run imprecision, commercial controls, patient samples

nije evidentirano