Precision and long-term stability of different estradiol immunoassays assessed in a multi-center quality control study

BACKGROUND

Because of the vast range of physiological relevant estradiol concentrations the requirements to be met by an estradiol assay are high. In the present study the performance of various commercially available estradiol assays was evaluated with regard to imprecision and long-term stability.

METHODS

Precision and long-term stability of 7 commercially available estradiol immunoassays were assessed in a multi-centre quality control study based on the repeated measurement of liquid BIOREF estradiol control sera by 18 laboratories during a 14-month study period.

RESULTS

The mean estradiol concentrations determined in 594 runs performed for each control level were 71 pg/ml, 349 pg/ml and 676 pg/ml. A high variation was found for the method specific mean values calculated from all results measured with the same method, which ranged between 32 - 90 pg/ml, 187 - 392 pg/ml and 373 - 790 pg/ml, resulting in a similar high inter-laboratory variation with coefficients of variation (CVs) of 25.0%, 16.7% and 17.5%. In contrast, the intra-laboratory variation of estradiol values as well as the variation of values measured with the same method were found to be considerably lower with coefficients of variation < 10% for most laboratories and methods; only the low control level was measured with CV values > 10% by the majority of laboratories and methods. For none of the laboratories a tendency was observed in the results from beginning to end of the 14 month study period indicating a high uniformity in assay production and a good long-term stability of the control material used.

CONCLUSIONS

The present data demonstrate that also with the currently available estradiol immunoassays the comparability of results measured with different methods is limited. With most assays very low estradiol concentrations, as observed in postmenopausal women, can be determined only with a precision which is not adequate for clinical assessment.

Results of the multicentre evaluation of an electrochemiluminescence immunoassay for HCG on Elecsys 2010

This study evaluated the performance of the HCG STAT Elecsys assay in 8 European laboratories using the Elecsys 2010 system. Analytical sensitivity was < 0.5 mlU/mL. The analysis of concentration series prepared by mixing serum pools with high and low HCG concentrations proved linearity up to 10.000 mIU/mL. A high-dose hook effect was not seen up to HCG concentrations of 430.000 mIU/mL. The medians of the within-run CVs (n = 21, 3 series) were 3.0% (2.1-5.8% CV; 10.4-14.4 mIU/mL), 2.4% (1.7-6.1% CV; 35.6-88.6 mIU/mL) and 2.3% (1.7-6.1% CV; 282.3-643.8 mIU/mL). The medians of the between-day imprecisions (n = 10-21) were 7.0% CV (5.2-12.0% CV; 4.0-14.0 mIU/mL), 5.5% CV (3.1-7.2% CV; 35.4-92.7% mIU/mL) and 4.1% CV (2.8-5.1% CV; 270.8-658.0 mIU/mL). The median recovery of two external quality control samples with assigned values of 9.39 and 10.40 mIU/mL) were 101.2 and 104.3% (ranges: 94.8-116.1%, 98.6-117.8%, n = 10). The assay was compared with five non-isotopic automated routine immunoassay systems (x). Slopes ranged from 0.87 to 1.15 and intercepts from-0.53 to 12.50 mIU/mL. The coefficients of correlation were with one exception (0.898) > or = 0.960. The distribution of HCG in samples from non-pregnant women and healthy men was very similar to that observed with other automated routine methods. The HCG Elecsys assay is very specific for the intact holo-hormone. Nicked HCG dimer, nicked and non-nicked beta-subunits are weakly recognised or not detected. Hemoglobin, bilirubin and lipemia (tested up to: Hb, 3.7 g/L; bilirubin, 500 mumol/L; triglyceride, 37.6 mmol/L) did not interfere the assay. The HCG Elecsys assay is well suited for the early and fast diagnosis of normal pregnancy and the detection of tubal pregnancy.

Elecsys TSH, FT4, T4, T-uptake, FT3 and T3. Clinical results of a multicentre study

6 assays for the assessment of thyroid function (TSH, FT4, T4, T-uptake, FT3 and T3) were targets of the International Multicenter Study on the random access analyzer Elecsys 2010. The aim of the study was to characterize the clinical performance of the assay in method comparison and reference range studies. The assays under evaluation were compared to a broad variety of radio isotopic and non-radio isotopic assays. They are suitable for serum and plasma samples. In case of TSH the study include 2nd and 3rd generation TSH procedures. In general, good to excellent correlations were found between the Elecsys and the respective routine methods. Systematic deviations were extraordinary low in case of TSH, FT4 and T4. Regarding the analysis of T3 and FT3 some systematic deviations in terms of standardization have been observed. Results of Elecsys T4 and Elecsys FT4 were independent of the serum total protein or serum albumin concentrations. In T3 and FT3 Elecsys the results of samples from NTI (non-thyroidal-illness) patients were decreased, reflecting the physiological situation in these patients. Studies using samples from healthy euthyroid as well as untreated hypo- and hyperthyroid individuals enabled us to assess the assays reference ranges.