Cobo Athlete Biological Passport Visualization and Discussion

Its blood data, so you know I have to take a look. The UCI broke its long biopassport sanction drought by going after a retired rider on a minor team best know for blowing things up at the Vuelta. The upshot is they handed the red (formerly gold) jersey to Froome who rode said Vuelta, after a failed sale to Bruyneel, and got shuffled into the starting roster when Sky ran out of other riders to slot in the race.

Above are my recreations of what the ABP would look like based on using the rolling mean and 2.3 SDs (99th percentile cuts) up to but excluding the plotted time point, ie what the ABP software would have pinged/not pinged at the time of the sample. See my work here: https://drive.google.com/file/d/1DHANbgQbOv3tbTsEOmh4uxKzAjiVK0vJ/view?usp=sharing

For the rationale of how a z-score model (the plotted thing above) effectively replicates the ABP once you get more than a handful of points see our paper:

This assumption is supported by previous work showing that z-score thresholds generated from an individual athlete’s data alone converge with the ABP model thresholds and demonstrate comparable classification performance once both models are trained on sufficient baseline data (Sottas et al., 2007).  https://www.frontiersin.org/articles/10.3389/fphys.2018.00643/full

Also, note that the plot for reticulocytes shows the square root values. This transformation is necessary to normalize the distribution so that the SD gives the same percentiles above and below the mean. And sub-note that the ABP software use Hgb and Off-score but not the reticulocyte percentage. The reticulocytes however are a go to for the experts reviewing the data as they are not affected by the plasma volume swings that occur with thing like a grand tour.

Disclaimer: I am not making promises that I didn’t make any transcription errors, but I did my best.

The UCI/WADA summed up its position as:

The ABP in the case at hand is based on the Expert Panel’s initial evaluation of 38 valid samples,12 the documentation of which was included as evidence in the UCI’s submissions. As reported by the Expert Panel, the main important abnormalities in the Rider’s profile are (i) the significant variability of haemoglobin concentration (HGB) with a 95% sequence abnormality, (ii) the variability of reticulocytes (0.28-1.43%), which, according to the Expert Panel, is “above the physiological range, with 99% sequence abnormality” and (iii) the 92% sequence abnormality of the OFF-score values, including several high values (122 in sample 46, 121 in sample 17, 120 in sample 18, 117 in samples 16, 31, 38, 42 and 47). see: https://www.uci.org/docs/default-source/clean-sport-documents/anti-doping-tribunal/uci-adt-03.2018-uci-v.-mr-juan-jos–cobo-acebo.pdf

So what I find interesting, assuming that I didn’t screw things up, is that the software, in real time would not have pinged a beyond threshold value until the low Hgb on July 16, 2012 which doesn’t seem to feature in the decision. Instead, their only sanction-able finding was:

… wait for it

… wait for it

they didn’t actually have one as far as I can tell according to WADA rules, which are kindly summarized for ABP data in the “Factual Background” section:

Haematological data is considered atypical if 1) a haemoglobin (HGB) and/or OFF-score (OFFS) marker value falls outside the expected intra-individual ranges, with outliers corresponding to values out of the 99%-range (0,5 – 99,5 percentiles) (1:100 chance or less that this result is due to normal physiological variation) or 2) when sequence deviations (a longitudinal profile or marker values) are present at specificity of 99,9% (1:1000 chance or less that this is due to normal physiological variation).

See the issue is that the most wildly abnormal thing in Cobo’s passport is the 0.28 reticulocyte percentage value on 9/26/2019. To get that low you are talking about coming off of old-school doses of EPO or a full bag or two of packed red blood cells. However, according to my most recent readings of WADA code, the reticulocyte values can only be used as supporting evidence. The main line of evidence from the ABP must either be the Hgb or Off-score with values or sequence outside of 99% or 99.9% respectively. Cobo only got to 95% and 92% sequence abnormality on the Hgb and Off-score respectively.

This case then raises two questions:

  1. Is “expert (gestalt) opinion” now good enough to sanction a rider.
  2. How the does Cobo full-tilt doping not flag the passport.

Question 1, hopefully someone with legal side knowledge can chime in on.

Question 2, the answer is this:

If you dope, dope consistently. Why? The model only knows what you teach it, again from the frontiers paper:

Interestingly, neither the performances (Figure 3C) nor the parameter estimates (Figures 3D,E) for “doped” 2008 fell outside the prediction intervals. This result highlights a limitation in “passport-type” detection methods in which the “doped” 2007 data were included in the model training and biased the means and increased the variance such that the “doped” 2008 performances and parameter estimates were not statistically detected.

(Image reproduced for educational purposes only.)

Its a problem that I’ve wondered about quite publicly for a while without much response from the official anti-doping community, and more formally illustrated it with the easter egg line/figure in the Frontiers paper. Now, we have a real live in the flesh illustration. Satisfying, to be proven right by a GT winner, but sad for cycling/sports etc.