Tritium/Carbon-14 Urinalysis Intercomparison - May 2002

Results

Samples were distributed to nine laboratories. Eight returned results as requested. These results are presented in Table 1.

The equations used to evaluate the bias and precision of results are given in the appendix. The terms used in the equations and the attached tables and figures are defined as follows:

y_jkl =   the result obtained by correcting the measurement for a spiked sample by the value obtained for the appropriate urine blank.

b_jkl =   the relative bias of the result obtained for each aliquot of a particular spiked sample. It represents the difference between the measurement and the true value, normalized by the true value.

b_jk =   the mean relative bias, i.e. the mean of the bjkl values for a particular spiked sample.

s_jk =   relative precision, calculated as the standard deviation of the relative bias of measurements of aliquots of the same spiked sample.

MDA =   Minimum detectable activity. This is an indication of the detection capability of a participant's analytical method.

MTL =   Minimum testing level. The minimum amount of radioactive material at which a dosimetry service should be tested for it to be in compliance with the Canadian Nuclear Safety Commission (formally the Atomic Energy Control Board) license requirements for performance in an independent testing exercise.

The CNSC has set its performance criteria for bioassay measurements in Regulatory Standard S-106, "Technical and Quality Assurance Standards for Dosimetry Services in Canada"[3]. At levels equal to or greater than the MTL, the limits for acceptable bias and precision are:

| -0.25 <= Mean relative bias <= +0.50 |

| Relative precision <= 0.40 |

Note that the MTL is set at five or more times the MDA. In S-106, the MDA for urinalysis has been set at 70 Bq/L for carbon-14 and at 400 Bq/L for tritium. The known performance of Canadian bioassay laboratories has been taken into consideration in setting these specifications [3].

Relative Bias:

The y_jkl values and their means are listed in Table 2. The y_jkl values are also presented graphically in Figures 1 and 2.

The b_jkl values are presented in Table 3. All values were within the acceptable relative bias limits.

Table 4 lists the b_jk values which are also shown in Figures 3 and 4. All values satisfied the performance criteria for mean relative bias.

Relative Precision:

The s_jk values are presented in Table 5 and Figures 5 and 6. All values were within the acceptable limit for relative precision.

For the participants that followed the recommended protocol (all laboratories in this intercomparison) of only one analyst performing measurements for all the blank and spiked samples, the s_jk values indicate day-to-day within-analyst variability in addition to intra-laboratory precision.