
New study casts doubt on some fingerprick blood tests - pavornyoh
http://arstechnica.com/science/2015/11/new-study-spills-doubt-on-some-fingerprick-blood-tests/
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Fede_V
If this study is correct, and blood drops have a high variability in certain
important clinical features, then, no matter how accurate the instruments are,
it's impossible to actually get a clean measurement from low volumes of blood.

This is one of the most obvious tests that should come to mind for anyone who
wishes to create a blood diagnostic company. How could Theranos not know about
this?

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danieltillett
More importantly how did their sophisticated investors not know this? This
issue has been known in the industry for years.

The whole Theranos fiasco would not matter except for the damage it does to
other biotech startups - when sentiment turns it does not matter if what you
are doing is real or not, everyone is frozen out.

~~~
FireBeyond
I highly doubt their sophisticated investors are any more clued in than their
board / executive management, which included prominent military figures,
industrial complex powerbrokers, politicos, but zero or nearly zero medical
expertise.

~~~
danieltillett
I need to be a little less subtle with my snark I think. If there ever was a
company you could have avoid investing in by looking at their board it is
Theranos [1].

1\. [https://www.theranos.com/leadership](https://www.theranos.com/leadership)

~~~
mkehrt
_Kissinger?!_

~~~
FireBeyond
Go figure, right? "Awarded the Nobel Peace Prize" \- and also generally
considered guilty of war crimes if we're to use the rules of Nuremberg.

Oh, and Bechtel (nuclear, defense), Cargill (hedge funds on the back of
deforesting rain forests to grow more soy), antitrust lawyers, Marine Corps
General, ex-Armed Services Committee Senators, a Secretary of Defense, a Navy
admiral - oh, and an epidemiologist and surgeon. Very unusual leadership.

~~~
danieltillett
The surgeon was the ex-leader of the senate. We are just left with a war
cabinet and epidemiologist.

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moultano
I've found even glucose meters to be wildly inaccurate. There is often a 20%
difference in readings between two meters moments apart, and thats enough to
have consequences for how your care is managed.

~~~
RA_Fisher
It's pretty heteroskedastic, which practically makes the errors not tooo bad.
For example, say my wife is low (< 70), in that case the error rate will be
small. That's where precision matters. Now suppose she's 200+, in that case
the errors will be large but it doesn't really impact how to take care of it.
In terms of error, What worries me much more is a server at a restaurant
giving my wife a regular coke rather than a diet coke or vice versa.

Where smaller blood is really beneficial is that it requires a less painful
finger prick.

~~~
Fede_V
If the error is proportional to the measurement - can't you just take the log
to make it additive again?

~~~
RA_Fisher
Hmm, it's not clear to me what the benefit of that would be in terms of
information (a transformation). It's univariate data, it's been a bit since I
looked at it but a histogram showed readings were lognormal / weibull / gamma
distributed (point is asymmetric, right-skewed), I believe.

In terms of inference, it's kind of mind-bending to think of a "population" of
blood and each person having a specific variation.

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cant_kant
Fingerpricks provide capillary blood mixed with tissue fluid.

A venupuncture provides venous blood.

The normal ranges and the error bars are different for finger prick
blood.Virtually data and research on the normal ranges and ranges in various
diseases has been done on venous blood.

The thousands of journal articles that come out each week are done using
results of venous blood.For instance, see this article from this week's NEJM
[http://www.nejm.org/doi/full/10.1056/NEJMoa1504720?query=fea...](http://www.nejm.org/doi/full/10.1056/NEJMoa1504720?query=featured_home#t=articleMethods)
The glycated Hb readings referred to in this article are automatically taken
to be on venous blood samples, as are the fasting glucose levels.

Your physician relies on readings from venous blood. His training in medical
school was on normal and pathological ranges in venous blood samples.

Physicians are thrown a bit when given pathology readings from other countries
( mmol versus the old fashioned American mgs/litre are confusing. if the
pathology printout is in German or Arabic, it adds even to the fun ). It
breaks the flow of rapid data analysis while the physician breaks out bc
[https://www.gnu.org/software/bc/](https://www.gnu.org/software/bc/) or some
other calculator to convert units.

Add in the confusion and inaccuracy of fingerprick samples, and the potential
for even more error, increases a bit.

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m0rganic
My wife's a nurse and she said if the test comes out high or low they always
do a blood draw to double check. So this doesn't seem that ground breaking of
a study.

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tedunangst
What do they do if the test erroneously comes out normal?

