Endocrine Abstracts

Introduction: The limit of quantification (LOQ) is defined as the lowest analyte concentration that can be reproducibly measured with defined imprecision expressed as CV (coefficient of variation). Low concentrations of hormones estradiol, LH, FSH and testosterone are essential in diagnosis and monitoring of various endocrine disorders. Automated immunoassays have well known advantages, but still limited in achieving necessary analytical sensitivity. The major concern is to produce low values with low imprecision. Our aim was to determine the lowest concentration of the listed hormones with CV <20%.

Aterials and Method: According to LOD (limit of detection) and LOQ declared by the manufacturer we selected similar estradiol, LH, FSH and testosterone concentrations. Serum pools were prepared from patients residual samples. Final pool concentrations were: (i) estradiol 88,9 pmol/l, 50,7 pmol/l and 27,4 pmol/l; (ii) LH and FSH 0,3 IU/l; (iii) testosterone 0,5 nmol/l and 0,17 nmol/l. Pools were analyzed over five days in triplicates on Roche Cobas e801 and CV was calculated. Inter-assay variation (bias) was eliminated by analyzing all specimens in a single batch using a single instrument, one analyst, one set of calibrators with the same lot of reagents.

Results: The determined CV for estradiol at 88,9 pmol/l, 50,7 pmol/l and 27,4 pmol/l was 6,0%, 9,3% and 19%, respectively. The remaining pools obtained CVs as follows: 4% for LH at 0,3 IU/l; 2,3% for FSH at 0,3 IU/l; 4,9% and 7,8% for testosterone at 0,5 nmol/l and 0,17 nmol/l.

Conclusion: All selected estradiol, LH, FSH and testosterone concentrations met the defined criteria of CV <20%. Therefore, they represent the reliably measured low concentrations on analytical system Roche Cobas e801 and could be defined as LOQ.