I've been doing some work with the i2b2 unit conversions. Note we are on 1.7,
so I can speak to earlier versions - it might work, it might not. Some of you
may already be using this capability.... I2b2 supports client side units
conversion but also has server side units conversion capability. I'll attempt
to explain below...
H2
_____________________________________
.
A normal numeric query with the default project setting (the above not set or
set to OFF) Yields the following SQL when searching for patients with a weight
<= 1600 ounces (we are storing weights in ounces):
insert into BlueHeronData.QUERY_GLOBAL_TEMP (patient_num, panel_count)
with t as (
select /*+ index(observation_fact fact_cnpt_pat_enct_idx) */ f.patient_num
from BlueHeronData.observation_fact f
where
f.concept_cd IN (select concept_cd from BlueHeronData.concept_dimension
where concept_path LIKE '\i2b2\PCORI\Vitals\Weight\%')
AND ( modifier_cd = '@' AND (( valtype_cd = 'N' AND nval_num < 1600
AND tval_char IN ('E','LE')) OR ( valtype_cd = 'N' AND nval_num <= 1600 AND
tval_char = 'L' )) )
group by f.patient_num
)
In the project parameters, add the parameter CRC_ENABLE_UNITCD_CONVERSION and
set it to ON
Enabling this server side unit conversion for i2b2 with no other change yields
the following SQL generated:
insert into BlueHeronData.QUERY_GLOBAL_TEMP (patient_num, panel_count)
with t as (
select /*+ index(observation_fact fact_cnpt_pat_enct_idx) */ f.patient_num
from BlueHeronData.observation_fact f
where
f.concept_cd IN (select concept_cd from BlueHeronData.concept_dimension
where concept_path LIKE '\i2b2\PCORI\Vitals\Weight\%')
AND ( modifier_cd = '@' AND (( valtype_cd = 'N' AND case
when units_cd = 'OUNCES' then nval_num end < 1600 AND tval_char IN
when units_cd = 'OUNCES' then nval_num end <= 1600 AND tval_char = 'L' ))
)
group by f.patient_num
)
Note that the units_cd now appear in the query by default, as specified in the
c_metadataxml field
Adding in the conversion units to the metadata xml, and searching for patients
with a weight < 100 lbs yields:
insert into BlueHeronData.QUERY_GLOBAL_TEMP (patient_num, panel_count)
with t as (
select /*+ index(observation_fact fact_cnpt_pat_enct_idx) */ f.patient_num
from BlueHeronData.observation_fact f
where
f.concept_cd IN (select concept_cd from BlueHeronData.concept_dimension
where concept_path LIKE '\i2b2\PCORI\Vitals\Weight\%')
AND ( modifier_cd = '@' AND (( valtype_cd = 'N' AND case
when units_cd = 'POUNDS' then nval_num * 16
when units_cd = 'GRAMS' then nval_num * 0.035274
when units_cd = 'KILOGRAMS' then nval_num * 35.274
when units_cd = 'OUNCES' then nval_num end < 1600 AND tval_char IN
('E','LE')) OR ( valtype_cd = 'N' AND case
when units_cd = 'POUNDS' then nval_num * 16
when units_cd = 'GRAMS' then nval_num * 0.035274
when units_cd = 'KILOGRAMS' then nval_num * 35.274
when units_cd = 'OUNCES' then nval_num end <= 1600 AND tval_char = 'L' ))
)
group by f.patient_num
)
Note that in the i2b2 web client, the query shows up at < 1600 ounces even
though I specified <100 pounds in the dialog box for specifying weight.
If one now turns off CRC_ENABLE_UNITCD_CONVERSION then the webclient will
again ignore the units, and convert whatever ever units you specify to the
'normal units'.
My conclusions are :
* The server side flag that turns on the unit conversion machinery in i2b2
should be used if one has values in the fact table for findings or results with
heterogeneous units - e.g. some weights in pounds, some in kilograms, etc.
Note it is a global flag. If one turns it on, then all queries for numeric
results follow the pattern with specified units.
* If the units are always going to be homogenous, then no need to flip the
switch on the server side unit conversion - the i2b2 client will convert the
query to normal units if one uses one of the convertible units per the
metadataxml file
* Hence, in the case of weights there is no harm done in storing weights as
ounces (as Clarity does). That gives the best granularity for converting to
pounds/grams/kilos.
The metadata xml which contains the unit conversions used in the above testing
is :
<?xml version="1.0"?>
<ValueMetadata>
<Version>3.02</Version>
<CreationDateTime>06/11/2014 07:00:00</CreationDateTime>
<Loinc>3141-9</Loinc>
<TestID>LOINC:3141-9</TestID>
<TestName>Weight</TestName>
<DataType>PosFloat</DataType>
<Flagstouse>H</Flagstouse>
<Oktousevalues>Y</Oktousevalues>
<EnumValues></EnumValues>
<UnitValues>
<NormalUnits>OUNCES</NormalUnits>
<ConvertingUnits>
<Units>POUNDS</Units>
<MultiplyingFactor> 16 </MultiplyingFactor>
</ConvertingUnits>
<ConvertingUnits>
<Units>GRAMS</Units>
<MultiplyingFactor>0.035274 </MultiplyingFactor>
</ConvertingUnits>
<ConvertingUnits>
<Units>KILOGRAMS</Units>
<MultiplyingFactor>35.274 </MultiplyingFactor>
</ConvertingUnits>
</UnitValues>
<LowofLowValue>0</LowofLowValue>
<HighofLowValue></HighofLowValue>
<HighofHighValue>64000</HighofHighValue>
<LowofHighValue>64000</LowofHighValue>
</ValueMetadata>
From: Campbell, James R [mailto:[email protected]]
Sent: Tuesday, July 01, 2014 9:20 AM
To: Hickman, Hubert B; McClay, James C; Beard, Phillip; Phillip Reeder;
[email protected]
Cc: [email protected]
Subject: RE: Weight units
I am sure that the reason for Epic decision relates to newborn weights although
even there I think grams would be better. Phillip proposed a smallest common
denominator for measures and I am inclined to keep the ounces and add
conversion units for
grams to weight 3 kg
pounds for three kg and above with (kg appended). (175lb (79.9 kg)
I know metadataxml can convert the units but the question is do we need to
write any code to get a uniform display and query engine
________________________________
From: Hickman, Hubert B [[email protected]]
Sent: Tuesday, July 01, 2014 12:01 AM
To: Campbell, James R; McClay, James C
Subject: Weight units
Weight being stored in ounces (which seems to be its native form in Epic, sigh,
ugh) seems to be of little use to our target audience.
Our end users are not thinking in ounces, for sure. I would propose we convert
these to pounds or kilograms when we move them into the fact table (otherwise,
the unit conversion machinery in i2b2 will be used ALL the time, and my fear it
is going to be slow).
Unless somebody is a "YE OLDE ENGLISH PEDIATRICIAN" no medical person I know of
really thinks in ounces...
The heron code converts weights from ounces to pounds. Shall we follow suit?
Hubert Hickman
P/A III
The Nebraska Medical Center, Zip 5030
[email protected]<mailto:[email protected]>
(402) 559-4838
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