3. Establishing internal quality control

#### 3.1. Preparation of in-house internal quality control (IQC)

IQC samples are used to verify the validity of laboratory results. Correct results for IQC obtained in an assay give the confidence that the patients' results are correct. The IQC samples are assayed as part of the analysis, together with the standards and patients' samples. The matrix of the IQC samples should be the same as the patients' samples; in the case of urinary iodine, the matrix is human urine. We use the pooled patient samples since there is no commercial IQC for urinary iodine yet in the market.

Pooled patient samples are usually mixed, aliquoted and kept frozen until use. The advantages of pooled patient samples are:


The disadvantages are:


Every time we prepare a new batch of IQC, the same procedures ought to be followed:


b. Instrument print-outs

d. IQC performance reports (Levey-Jennings chart)

b. External quality assurance/proficiency testing reports

In management review meeting, the performance of the laboratory is discussed. Source of problems is identified and corrective actions suggestions from staff are noted for further actions.

IQC samples are used to verify the validity of laboratory results. Correct results for IQC obtained in an assay give the confidence that the patients' results are correct. The IQC samples are assayed as part of the analysis, together with the standards and patients' samples. The matrix of the IQC samples should be the same as the patients' samples; in the case of urinary iodine, the matrix is human urine. We use the pooled patient samples since there is no commercial IQC for urinary

Pooled patient samples are usually mixed, aliquoted and kept frozen until use. The advantages

• The determination of the concentration ranges is flexible since it can be adjusted accordingly

• They are often unreliable since there are no preservatives added as stabilizers and their

• The material is inexpensive since they are usually leftovers from the previous assays

• The IQC materials can be infectious since there is no screening prior to pooling

Every time we prepare a new batch of IQC, the same procedures ought to be followed:

d. Management review meeting (MRM) minutes

3.1. Preparation of in-house internal quality control (IQC)

c. Non-conformance reports (NCR)

3. Establishing internal quality control

c. Test results

78 Quality Control in Laboratory

iii. Post-analytical stage a. Test reports

iodine yet in the market.

The disadvantages are:

of pooled patient samples are:

• Same matrix as human sample

• The preparation of the IQC is time consuming

shelf life is often short (around 6 months)


The records of the IQC concentration range determination ought to be kept and referred to every time after assay. The IQC values obtained in an assay are compared to the mean 2SD values. Then, the IQC plotter charts are drawn (Levey-Jennings chart). Example is as depicted in Figure 7. The results should be checked; if the IQC values are within the ranges, the respondents' results are considered acceptable and could be reported. If the IQC values are out of range, the respondents' results are unacceptable for reporting and analytical problems need to be identified and solved. Daily IQC performance is very important in laboratories. It is very crucial to use fresh IQC samples in every assay. The IQC samples should be treated the same as treating the respondent samples.

#### 3.2. Procedural steps in IQC preparation

	- Low pool (L): 30–90 μg/l (e.g. target to get mean around 60 μg/l)
	- Medium pool (M): 110–130 μg/l (e.g. target to get mean around 120 μg/l)
	- High pool (H): 200–300 μg/l (e.g. target to get mean around 250 μg/l)

10. Spike of urine samples with potassium iodate ought to be avoided since it is more unstable as compared to using the endogenous iodine in the urine matrix.

#### 3.3. Monitoring QC performance through Levey-Jennings chart

QC results should be checked every time after an assay. There are some rules to refer to when deciding to accept an assay:

Accept assay when QCs are within 2 SD

Reject assay when any QC exceeds �3SD

Reject assay when 2 consecutive QCs exceed �2 to 3 SD

Reject assay when difference between 2 QCs exceeds �4 SD

QC performance should be reviewed regularly to check the precision and accuracy of the assay. Both the acceptable and unacceptable results should be recorded. Corrective actions taken when QC results are unacceptable should also be recorded. Example of Levey-Jennings chart is as depicted in Figure 7.

3.4. Non-conformance troubleshooting

Figure 7. Example of Levey-Jennings chart to monitor IQC performance.

step from the problem to occur again in future.

4. Participation in External Quality Assurance program

If the mean value of the IQC samples is outside the range, the results for respondents in the same range cannot be reported yet and testing should be repeated. The QC charts (Levey-Jennings charts) trends should be checked and the drift in accuracy should be monitored. The cause of drifts should be investigated, e.g. faulty instruments (may cause systematic errors), expired reagents or IQC samples (may cause systematic errors), unclean glassware (may cause random errors) or changes in the laboratory environment (any contamination from iodized salt or elevated temperature may cause systematic errors), or human error (e.g. new operator assigned for the test may cause random errors). The investigation outcome is then comprehended among laboratory personnel and relevant trouble-shooting is taken. The trouble-shooting is recorded as corrective action and it is not a one-time solution to the current problem but also as a preventive

Understanding Quality Control with Urinary Iodine Estimation

http://dx.doi.org/10.5772/intechopen.74442

81

External Quality Assurance (EQA) is an ISO requirement, to confirm the quality of analysis. It shows the bias and precision of our assay and the position of our laboratory within the same

#### Example:

```
Target volume = V3 = 250 μl � 500 aliquots = 125,000 μl = 125 ml
Initial H pool concentration = M1 = 400 μg/l
Initial L pool concentration = M2 = 70 μg/l
Target concentration = M3 = 250 μg/l
Volume L pool to be added = V1 = X
Volume H pool to be added = V2 = Y
Target volume = V3 = 125
Formula 1: X + Y = 125; Y = 125 � X
Formula 2: M1V1 + M2V2 = M3V3; M1X+M2Y=M3V3
M1(X) + M2(Y) = M3(125)
M1(X) + M2(125 � X) = M3 (125)
M1 (X) + M2 (125) � M2 (X) = M3 (125)
M1 (X) � M2 (X) = M3 (125) � M2 (125)
(X) (M1 � M2) = 125 (M3 � M2)
X ¼ 125 Mð Þ 3�M2
     ð Þ M1�M2
X ¼ 125 250 ð Þ �70
     ð Þ 400�70
¼ 125 180 ð Þ
    330
¼ 22, 500
   330
= 68.18 ml
Y = 125 � X
= 125 � 68.18
= 56.82 ml
```
Table 2. Calculation to obtain the target values of control samples.

#### Understanding Quality Control with Urinary Iodine Estimation http://dx.doi.org/10.5772/intechopen.74442 81

Figure 7. Example of Levey-Jennings chart to monitor IQC performance.

#### 3.4. Non-conformance troubleshooting

10. Spike of urine samples with potassium iodate ought to be avoided since it is more unstable

QC results should be checked every time after an assay. There are some rules to refer to when

QC performance should be reviewed regularly to check the precision and accuracy of the assay. Both the acceptable and unacceptable results should be recorded. Corrective actions taken when QC results are unacceptable should also be recorded. Example of Levey-Jennings

as compared to using the endogenous iodine in the urine matrix.

3.3. Monitoring QC performance through Levey-Jennings chart

deciding to accept an assay:

80 Quality Control in Laboratory

chart is as depicted in Figure 7.

Initial H pool concentration = M1 = 400 μg/l Initial L pool concentration = M2 = 70 μg/l Target concentration = M3 = 250 μg/l Volume L pool to be added = V1 = X Volume H pool to be added = V2 = Y

Target volume = V3 = 125

M1(X) + M2(Y) = M3(125) M1(X) + M2(125 � X) = M3 (125) M1 (X) + M2 (125) � M2 (X) = M3 (125) M1 (X) � M2 (X) = M3 (125) � M2 (125) (X) (M1 � M2) = 125 (M3 � M2)

<sup>X</sup> <sup>¼</sup> 125 Mð Þ <sup>3</sup>�M2 ð Þ M1�M2 <sup>X</sup> <sup>¼</sup> 125 250 ð Þ �<sup>70</sup> ð Þ 400�70 <sup>¼</sup> 125 180 ð Þ 330 <sup>¼</sup> <sup>22</sup>, <sup>500</sup> 330 = 68.18 ml Y = 125 � X = 125 � 68.18 = 56.82 ml

Formula 1: X + Y = 125; Y = 125 � X

Formula 2: M1V1 + M2V2 = M3V3; M1X+M2Y=M3V3

Table 2. Calculation to obtain the target values of control samples.

Example:

Accept assay when QCs are within 2 SD

Reject assay when any QC exceeds �3SD

Reject assay when 2 consecutive QCs exceed �2 to 3 SD

Target volume = V3 = 250 μl � 500 aliquots = 125,000 μl = 125 ml

Reject assay when difference between 2 QCs exceeds �4 SD

If the mean value of the IQC samples is outside the range, the results for respondents in the same range cannot be reported yet and testing should be repeated. The QC charts (Levey-Jennings charts) trends should be checked and the drift in accuracy should be monitored. The cause of drifts should be investigated, e.g. faulty instruments (may cause systematic errors), expired reagents or IQC samples (may cause systematic errors), unclean glassware (may cause random errors) or changes in the laboratory environment (any contamination from iodized salt or elevated temperature may cause systematic errors), or human error (e.g. new operator assigned for the test may cause random errors). The investigation outcome is then comprehended among laboratory personnel and relevant trouble-shooting is taken. The trouble-shooting is recorded as corrective action and it is not a one-time solution to the current problem but also as a preventive step from the problem to occur again in future.
