Assay Precision & Accuracy

Trueness and Accuracy
The trueness of measurement can be defined as the closeness of agreement of between the average value obtained from large series of results of measurement and a true (actual) value. The difference between the average value and the true value is called the bias, which is inversely related to the trueness. Trueness can be evaluated by comparison of measurements by given method and a reference method. Such an evaluation may be carried out by parallel measurements of a set of test samples or by measurement of reference materials. The ISO has introduced the trueness expression as a replacement for the term “accuracy”. Accuracy is the closeness of the agreement between the result of measurement and a true concentration of the analyte. Accuracy is thus influenced by both bias and imprecision and in this way reflects the total error.

Precision
Precision may be defined as the clones of agreement between independent results of measurement obtained under specified conditions. The degree of precision is usually expressed on the basis of statistical measures of impression such as the SD or CV( CV= SD/mean), which thus is inversely related to precision. The imprecision of measurement is to random error and it is independent of trueness (accuracy) of measurements. Precision often depends on the concentration of the analyte being considered.

Repeatability:
The closeness of agreement between results of successive measurements carried out under the same condition (i.e. corresponding to within-run precision).

Reproducibility:
The closeness of agreement between results of measurement performed under a changed condition of measurements (e.g. time, operator, calibrations and reagent lots). The precision can be used as intra-assay (within-run) and inter-assay (between-run) precision. To estimate the variation or imprecision, a common approach is to measure duplicate samples in a series of runs. And the estimate of the imprecision improves the more observations are available.

Model of Precision and Accuracy. Precision and Accuracy are independent parameters for given assay

Additional Concepts
Recovery: Recovery is the fraction or percentage increase of concentration that is measured in relation to the amount added. A recovery close to 100% is a prerequisite for a high degree of trueness, but it does not ensure unbiased results because possible non-specificity against matrix components is not detected in a recovery experiment.

Drift is caused by instrument instability over time, so that calibration becomes biased.

Comments

MCQs on Neisseria gonorrhoeae and Neisseria meningitidis: Medical microbiology

Multiple Choice Questions on Neisseria species (Gram-negative cocci) 1) A 19-year-old female college freshman, presented to the university health center with a severe headache, fever, and a stiff neck. She lived in a dormitory and was active in various social activities. She had received all her childhood vaccinations but had not received a booster for the meningococcal vaccine recommended before college entry. Clinical Presentation: On day 1, the patient experienced a sudden onset of fever (39.5°C or 103.1°F), severe headache, nausea, and vomiting. She also noticed a rash on her trunk and legs. Over the next two days, her symptoms deteriorated further, leading to photophobia and altered mental status. Concerned, her roommates brought her to the university health center. Physical Examinati...

Multiple Choice Questions (MCQs) on Diabetes Mellitus: Pathogenesis, Diagnosis and Treatment

MCQs on Diabetes mellitus 1) Diabetes mellitus is a disorder characterized by hyperglycemia. Which of the following is not the common characteristic features of type 2 diabetes mellitus ? a) Impaired insulin secretion b) Increased Insulin resistance c) Diabetic ketoacidosis d) Excessive hepatic glucose production 2) Which of the following are the characteristic features of type 1 diabetes mellitus? a) Type 1 diabetes is caused by an absolute deficiency of insulin. b) Type 1 diabetes is associated with the autoimmune destruction of beta cells. c) Patients with uncontrolled type 1 diabetes present with diabetic ketoacidosis d) All of the above 3) Which of the following serum measurements are not used for the diagnosis of diabetes mellitus? a) Fasting blood glucose d) Postprandial blood glucose c) Insulin ...

Pentose Phosphate Pathway: Source of NADPH for Reductive Biosynthesis (Biochemistry)

Introduction to Pentose Phosphate Pathway The pentose phosphate pathway ( Hexose monophosphate pathway ) is the metabolic pathway that occurs in the cytosol and generates NADPH (nicotinamide adenine dinucleotide phosphate) which is utilized in various biosynthetic pathways. This pathway can be broadly classified into two phases i.e oxidative phase and non-oxidative phase. In the oxidative stage of the pentose phosphate pathway, the glucose-6-phosphate is converted to five carbon ribulose-5 phosphate with generation of NADPH. During the non-oxidative stage, the interconversion of pentose sugars and hexose sugars is catalyzed by isomerases and aldolases. The fate of these reversible steps depends on the anabolic and energy status of the cells. The two primary functions of the pentose phosphate pathway are ; a) Provide NADPH (a coenzyme) for biosynthetic pathways b) Provide pentose sugars for nucleotides (DNA and RNA) synthesis Two phases of Pentose phosphat...

BIOCHEMISTRY, BIOMEDICINE & PHARMACEUTICS

Search This Blog