It is a mandated part of quality management system of a lab as per ISO. This has to be an ongoing process and should include monitoring of accuracy and precision. Only accurate, precise results are meaningful for diagnosis and prognosis. The two salient parts of Quality Assurance are Internal Quality Controls and External Quality Assurance.

Internal quality control material is usually run at the beginning of each shift, after an instrument is serviced, when reagent lots are changed, and whenever patient results seem inappropriate. The number of QC levels run and the number of runs per day and the location of the QC runs is as per the labs protocol and quality specifications of the labs as per each analyte’s performance.

** Quantitative examinations** measure the quantity of an analyte present in the sample, and measurements need to be accurate and precise. The measurement produces a numeric value as an end-point, expressed in a particular unit of measurement. Such tests can use controls that produce numerical results and can be monitored through statistical processes to understand the stability of the analytical system.

** Qualitative examinations** are those that measure the presence or absence of a substance, or evaluate cellular characteristics such as morphology. The results are not expressed in numerical terms, but in qualitative terms such as “positive” or “negative”; “reactive” or “non-reactive”; “normal” or “abnormal”; and “growth” or “no growth”. Controls of such tests do not yield numerical and hence cannot be monitored through statistical processes.

Semi-quantitative examinations are similar to qualitative examinations, in that the results are not expressed in quantitative terms. The difference is that results of these tests are expressed as an estimate of how much of the measured substance is present. Results might be expressed in terms such as “trace amount”, “moderate amount”, or “1+, 2+, or 3+”. Controls of such tests do not yield numerical and hence cannot be monitored through statistical processes.

1. The IQC should be cost effective.

2. In the case of IQCs with numerical values;

4. Controls should have long expiry.

5. The shelf life and open vial stability of the control should be good, with minimal vial to vial variability.

Dehydration process is typically used to preserve a material or make the material more convenient for transport. Freeze-drying works by freezing the material and then reducing the surrounding pressure to allow the frozen water in the material to sublimate directly from the solid phase to the gas phase. Such lyophilized material require careful reconstitution before use

** Matrix effect –** the influence of the control material’s matrix, other than the concentration of the analytes, on the measurement procedure that produce differing results, while still producing consistent results on patient samples, is called the matrix effect

The normal distributions are a very important class of statistical distributions. All normal distributions are symmetric and have bell-shaped density curves with a single peak. Here, all the measures of central tendency –mean, median and mode – are at the same point. The normal distribution is also called the Gaussian distribution. Some details about normal distribution are as follows.

S.No | Rule Violation | Systemic error | Random error |

1 |
1:2_{s} |
√ (beginning) | √ |

2 |
2:2_{s} |
√ | |

3 |
2 of 3_{2}S |
√ | |

4 |
R_{4s} |
√ | |

5 |
1:3S |
√ (beginning) | √ |

6 |
4_{1}S |
√ | |

7 |
6x,8x,9x,10x,12x |
√ (beginning) | √ |

8 |
7 _{T} |
√ (beginning) | √ |

For the new QC, at least 20 data points must be collected over a 10-20 day period. When collecting this data, be sure to include any procedural variation that occurs in the daily runs; for example, if different testing personnel normally do the analysis, all of them should collect part of the data. Once the data is collected, the laboratory will need to calculate the mean and standard deviation of the results and assign these for further monitoring of the system.

In case of QCs short expiry QCs, the mean may be gathered by doing 4-6 runs in 2 days. To this the CV% of the running/ current lot may be applied to derive the SD.

**Repeatability**is a condition of measurement, out of a set of conditions that includes the same measurement procedure, same operators, same measuring system, same operating conditions and same location, and replicate measurements on the same or similar objects over a short period of time. Repeatability may be expressed in terms of multiples of the standard deviation. Within-run/ Intra-serial/Intra-run precision condition is synonyms.**Reproducibility**is precision under reproducibility conditions, i.e. conditions where test results are obtained with the same method in different laboratories, by different operators, using different equipment, in different laboratories, in different locations, or on different days. Reproducibility may be expressed in terms of multiples of the standard deviation. Between Laboratories/ Inter Laboratory/Among Laboratories are synonyms**Intermediate**Precision Is something between the 2 states, generally meaning with one lab, but with changes of reagent and calibrator lots, operators, operating conditions. All acceptable laboratory variables will be captured if at least 100 measurements are included. The**Uncertainly of Measurement (MU)**uses intermediate precision as the basis for its calculation

Where SE = Inaccuracy (Accuracy is the closeness of a measurement to its target/ true value. SE or Bias = Lab Mean – Target Value).

RE = Computed Imprecision (Precision is the amount of variation in the measurements, a deviation away from an expected result, expressed in the unit of dispersion, the SD. SD is then multiplied by a coverage factor usually, 1.65)

18. What is Total Allowable Error? How does it help if you know the total error you make in the lab?

Total Error enables the lab to understand where it stands in terms of quality. The lab can compare its error to the quality specifications available for each analyte. This specification is called Total Allowable Error or TEA

Total Allowable Error (TEA) is the amount of error that can be tolerated without invalidating the medical usefulness of the analytic result. A commonly used quality requirement is Total Allowable Error (TEA), which is derived from medically important analyte concentrations or clinical decision thresholds.

A hierarchy of quality requirements has been proposed

1. Medical Requirements

2. Biological Variation

3. Proficiency testing guidelines

4. Using Proficiency Testing results (past survey report)

5. Tonk’s Rule

6. Current Lab (Observed) CV *3

SEc= {(TEa- Absolute Bias) / SD} – 1.65

**Standard Deviation Index **)-Peer-based measure of bias Describes how far our mean is from the peer or all lab methods’ mean Has direction, + or - . It is an indicator of accuracy.

CVI (**Coefficient of Variation Index**) Peer-based measure of imprecision Comparison of our laboratory's CV to the peer or all-lab CV It is also known as Coefficient of Variation Ratio (CVR). It is an indicator of precision.

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