Here's another study where the same samples were not only sent to different labs. but resubmitted later.
To evaluate intra- and inter-laboratory agreement concerning hair mineral analysis and interpretation of results, hair samples from 2 volunteers were sent to seven laboratories, which commercially offer hair mineral analysis in Germany. 6 weeks later, another identical part from the hair sample of volunteer 1 was sent to all seven labs. Altogether, 50 elements were analyzed, 23 by all seven labs. For comparability, only the results for these 23 elements were assessed. The intra-laboratory reproducibility was evaluated by the 2 identical hair samples from volunteer 1. On the average, the reproducibility seems to be sufficient (median +/- 9.48% to +/- 20.59%), but for individual elements there were unacceptable out-rulers up to 100%. Only one lab classified all elements of the first and the second analysis of the identical hair sample in the same category (below, within, or above normal range). The others grouped 4 to 7 elements different. This is not tolerable. The inter-laboratory comparability was assessed by the results of the hair samples of both volunteers. For the sample of volunteer 1 at least the results of 6 (out of 23) elements were within an acceptable range of +/- 30% from the consensus value (= mean of all seven labs). For volunteer 2 this was only the case for 2 (!) elements. Differences of more than 100% were found for most other elements. Moreover, in the vast majority of the tested elements there was no comparability of the cLassification to the respective reference ranges of the different laboratories. For example, for volunteer 1 only 3 elements (our of 23!) were identically classified by all seven labs. As neither the analytical results nor the classification to the individual reference ranges by the laboratories correspond in tolerable borders, conclusions, drawn from these results, cannot be valid. Hair mineral analysis from these laboratories is unreliable. Therefore we must recommend to refrain from using such analysis to assess individual nutritional status or suspected environmental exposure.