Rounding error blood glucose?

Question

Hi

For FDA compliance we are checking the data that is uploaded to HealthVault and the actual reading on the device. I noticed some rounding errors in blood glucose readings. The weird thing is that when i edit the blood glucose reading in HealthVault it shows the correct value!

For example: i have a reading showing 100 mg/dL in the overview but when i edit this reading in HealthVault it shows 99 mg/dL in the edit field! And 99 mg/dL is the correct conversion from mmol.

Can someone explain what is going on with the rounding?

This is a crucial issue for FDA compliance and it should be correct.

Peter 

Answer 1

What do you mean by when you mention overview?  Are you referring to this page:

The value displayed on the overview is dependent on a few things.  It's the value that was stored in the type during the add/edit as the "DisplayValue" for the measurement. If that "DisplayValue" is missing, then it'll show the stored value/units.

If you are seeing the overview above as mg/dL, then that is the value that was stored as the DisplayValue since HealthVault stores all BloodGlucose measurements as mmol and we do not do any rounding on the overview page shown above.

How was the data uploaded to HealthVault?

Answer 2

Yes i was referring to the image you show above. This is how i upload it to HealthVault

<blood-glucose><when><date><y>2012</y><m>4</m><d>5</d></date><time><h>15</h><m>9</m><s>55</s></time></when><value><mmolPerL>5.5</mmolPerL><display units="mg/dL" units-code="mg/dL">100.0</display></value><glucose-measurement-type><text>Whole blood</text></glucose-measurement-type><measurement-context><text>Before meal</text><code><value>16</value><family>wc</family><type>glucose-measurement-context</type><version>1</version></code></measurement-context></blood-glucose>

So it displays 100 mg/dL on the overview page but when I edit the entry it shows 99 and not 100. I have the feeling it is a rounding error in the conversion of 5.5 mmol to mg (5.5 * 18.0182 = 99.1) which is shown in the edit field. I will change the mmol to more decimals after the dot!

Answer 3

Update: It gets better if i do this. HealthVault edit shows now 99.9. Close enough to 100

<blood-glucose><when><date><y>2012</y><m>4</m><d>5</d></date><time><h>15</h><m>31</m><s>31</s></time></when><value><mmolPerL>5.55</mmolPerL><display units="mg/dL" units-code="mg/dL">100.0</display></value><glucose-measurement-type><text>Whole blood</text></glucose-measurement-type><measurement-context><text>None</text><code><value>0</value><family>wc</family><type>glucose-measurement-context</type><version>1</version></code></measurement-context></blood-glucose><common><note></note><tags>Category: None

Answer 4

If you want it displayed as 99 mg/DL, why do you have 

<display units="mg/dL" units-code="mg/dL">100.0</display>

If you want it 99, put 99 there.  The overview page will show whatever is saved in this <display units> xml.  The edit will always accurately use what is stored in the <mmolPerL> field and do any proper conversion.  This for example allows someone to put like 14 stones for the display value for weight, even though we don't support stones, it could be displayed in stones, but our editor would use the kilograms.