Personal Health Device Implementation Guide
1.0.0 - STU 1

This page is part of the Personal Health Device FHIR IG (v1.0.0: STU 1) based on FHIR R4. This is the current published version in its permanent home (it will always be available at this URL). For a full list of available versions, see the Directory of published versions

PHD Numeric Observation Profile

The Numeric Observation Profile is used when the PHD metric measurement is a scalar that may be dimensionless. Examples would be weight, body temperature, glucose concentration, pulse rate, oxygen saturation, steps take, calories burned, etc. Scalar measurements are the most common type of PHD measurement.

The measurement is a scalar when the PHD metric contains one of the following attributes:

Attribute Value Additional Information
Basic-Nu-Observed-Value 16-bit Mder SFLOAT 12-bit mantissa
Simple-Nu-Observed-Value 32-bit Mder FLOAT 24-bit mantissa
Nu-Observed-Value 32-bit Mder FLOAT Complex attribute. Also contains
metric-id
measurement status
unit-code

These attributes contain a measurement value that is a single number. The Mder SFLOAT and FLOAT encodings indicate both precision and the number of significant figures. The Observation.valueQuantity.value element is required to honor the reported precision. See the section Mder FLOATs and SFLOATs for instructions on handling Mder S/FLOATs and their encoding to the valueQuantity .

The structure definition for this profile is given here

Mapping Numerics to FHIR

The following table shows how the numeric attributes are mapped to FHIR. Since the FHIR Quantity also contains the units the Unit-Code attribute value is required to complete the picture. The MDC unit code needs to be mapped to UCUM. In most cases this mapping is straight forward, but there can be some examples which are tricky. The MDC_DIM_TICK for the RR interval is just the number of ticks. However, the tick unit is given by the MDS attribute MDC_ATTR_TICK_RES which is the number of ticks per second. So if MDC_ATTR_TICK_RES is 2048 and the RR measurement is 3092, that means the RR interval is 1.5 seconds. One could also express the measurement in Hertz. When the units are converted in this manner, the value must be converted appropriately.

Attribute FHIR coding
Basic-Nu-Observed-Value.value
Unit-Code.code		 Observation.valueQuantity.value
Observation.valueQuantity.code (as UCUM)
Observation.valueQuantity.system=”http://unitsofmeasure.org”
Simple-Nu-Observed-Value.value
Unit-Code.code		 Observation.valueQuantity.value
Observation.valueQuantity.code (as UCUM)
Observation.valueQuantity.system=”http://unitsofmeasure.org”
Nu-Observed-Value.value
Nu-Observed-Value.unit
Nu-Observed-Value.metric-id
Nu-Observed-Value.status		 Observation.valueQuantity.value
Observation.valueQuantity.system=”http://unitsofmeasure.org”
Observation.valueQuantity.code
effects Observation.code see Obtaining the Observation.code
handle measurement status see PHD Base Observation Profile

Meta Data Profile

The uploader shall populate the Observation.meta.profile with http://hl7.org/fhir/uv/phd/StructureDefinition/PhdNumericObservation indicating this resource is generated following the PHD Implementation Guide.

Conditional Create Identifier Generation

For a general description of the PHD Observation Identifier see the “PHD Observation Identifier” section in PHD Base Observation Profile. The table below lists the items that make up the identifier.

Entry value Additional information
device “PhdDevice.identifier.value” This value is the PHD IEEE EUI-64 system identifier
patient “Patient.identifier.value-Patient.identifier.system” or
provided logical id		 The dashes are part of the identifier.
When the service provider gives the PHG a pre-determined patient logical id the PHG creates no Patient resource and has no patient information. In that special case the provided logical id is used
type “Observation.code.coding.code” See Obtaining the Observation Code
value “Observation.valueQuantity.value” or
“Observation.dataAbsentReason.coding.code		 The numerical value of the measurement or
the data absent reason if the value is not present
units “Observation.valueQuantity.code” The UCUM code for the units
reported PHD timestamp “timestamp” See Generating the PHD Reported Time Stamp
supplemental types “Supplemental-Types.N-“ A sequence of 32-bit MDC codes separated by a dash

The final identifier is made by concatenating the entries above as follows:

  • “device-patient-type-value-units-reported PHD timestamp-supplemental types”

Additional Numerical Measurement Information

11073 20601 numeric metric measurements have some additional optional attributes that are used only for numerics. When they occur, these additional attributes provide further information about the measurement. An example of such a numeric-only additional attribute is one that describes the accuracy of the measurement. The accuracy is a measure of the deviation of the actual measurement from the reported measurement. Consequently, ‘accuracy’ is not a concept that makes any sense in the context of a measurement which is one or more of a finite set of enumerated codes such as a glucose-monitor meal association (breakfast, snack, fasting, etc.), and thus the attribute is not used in Enumeration metrics.

As in the PhdBaseObservation profile, an Observation.component element is used to contain the additional information. There are five metric attributes that give extra information about numeric-only measurements.

Accuracy

The Accuracy attribute gives the maximum deviation as an absolute value of the reported measurement from the actual measurement over the entire range of the measurement. The reported accuracy is, thus, static and does not vary over the range of the measurement. It shall be reported if the PHD provides it and it is not corrupted. It is in the units of the measurement itself. The entries are as populated as follows:

Observation.component element entry Additional Information
code.coding.code 67914 This is the MDC code for the Accuracy attribute
code.coding.system urn:iso:std:iso:11073:10101 Indicates the MDC coding system
code.text optional but Should contain the reference id MDC_ATTR_NU_ACCUR_MSMT along with any other additional text
valueQuantity.value the value This is accuracy value
valueQuantity.system http://unitsofmeasure.org Indicates the UCUM coding system
valueQuantity.code shall be the code of the primary measurement The code shall be the UCUM unit code

Alert Operational State

The Alert Operational State is currently only used in the Pulse Oximeter specialization. This attribute uses an ASN1-BITs field to indicate whether the alerts on a given limit (upper or lower) are on or off. When SET, the alerts are off. This is a state-type measurement and when this attribute is present, both the set and cleared states are reported. Three bits are defined thus there will be three component entries for each of the bits.

Observation.component element entry Additional Information
code.coding.code 68746.n 68746 is the MDC code for the Alert Operational State. ‘n’ is 0, 1, or 2 depending upon which bit is being reported.
code.coding.system http://hl7.org/fhir/uv/phd/CodeSystem/ASN1ToHL7 Indicates the ASN-1 coding system
code.text optional but Should contain the ASN1 name ‘lim-alert-off’, ‘lim-low-off’, or ‘lim-high-off’ for bits 0-2, respectively, along with any other additional text
valueCodeableConcept.coding.code ‘Y’ or ‘N’ ‘Y’ for bit set, ‘N’ for bit cleared
valueCodeableConcept.coding.system http://terminology.hl7.org/CodeSystem/v2-0203 Indicates the V2 binary coding system

Alert Operational Text String

This attributes provides a human readable string describing the lower and upper threshold limits. It is currently used only in the Pulse Oximeter specialization.

Observation.component element entry Additional Information
code.coding.code 68104 This is the MDC code for the Alert-Operational-Text_string attribute
code.coding.system urn:iso:std:iso:11073:10101 Indicates the MDC coding system
code.text optional but Should contain the reference id MDC_ATTR_AL_OP_TEXT_STRING along with any other additional text
valueString the strings These are the lower and upper limit strings

Current Limits

The Current-Limits attribute is currently only used in the Pulse Oximeter specialization. It gives the lower and upper threshold limits of whatever measurement is being monitored.

Observation.component element entry Additional Information
code.coding.code 67892 This is the MDC code for the Current-Limits attribute
code.coding.system urn:iso:std:iso:11073:10101 Indicates the MDC coding system
code.text optional but Should contain the reference id MDC_ATTR_LIMIT_CURR along with any other additional text
valueRange.low.value the value This is the lower limit
valueRange.low.unit optional  
valueRange.low.system http://unitsofmeasure.org Indicates the UCUM coding system
valueRange.low.code shall be the code of the primary measurement The code shall be the MDC unit code
valueRange.high.value the value This is the upper limit
valueRange.high.unit optional  
valueRange.high.system http://unitsofmeasure.org Indicates the UCUM coding system
valueRange.high.code shall be the code of the primary measurement The code shall be the UCUM unit code

Measurement Confidence 95

The Measurement-Confidence-95 attribute is currently used only in the Continuous Glucose specialization. The attribute gives a lower and upper bound with which the manufacturer is 95%confident that the actual reported measurement is within that bounds.

Observation.component element entry Additional Information
code.coding.code 68236 This is the MDC code for the Measurement-Confidence-95 attribute
code.coding.system urn:iso:std:iso:11073:10101 Indicates the MDC coding system
code.text optional but Should contain the reference id MDC_ATTR_MSMT_CONFIDENCE_95 along with any other additional text
valueRange.low.value the value This is the lower limit
valueRange.low.unit optional  
valueRange.low.system http://unitsofmeasure.org Indicates the UCUM coding system
valueRange.low.code shall be the code of the primary measurement The code shall be the UCUM unit code
valueRange.high.value the value This is the upper limit
valueRange.high.unit optional  
valueRange.high.system http://unitsofmeasure.org Indicates the UCUM coding system
valueRange.high.code shall be the code of the primary measurement The code shall be the UCUM unit code

Threshold Notification Text String

The Threshold-Notification-Text-String attribute is currently used only in the Continuous Glucose specialization. It provides a human readable string describing the thresholds. There are separate measurement objects that actually give the thresholds.

Observation.component element entry Additional Information
code.coding.code 68232 This is the MDC code for the Alert-Operational-Text_string attribute
code.coding.system urn:iso:std:iso:11073:10101 Indicates the MDC coding system
code.text optional but Should contain the reference id MDC_ATTR_THRES_NOTIF_TEXT_STRING along with any other additional text
valueString the string This is a textual description of the thresholds for the given measurement

Examples:

A basic simple numeric observation with a time stamp and a supplemental types attribute is shown in Pulse Rate Spot Measurement. Simple numeric measurements are common in PHDs.

An example of a NaN (not a number) measurement is shown in NaN Example. Note that the value element is absent and replaced by a dataAbsentReason element.

Consumer of the PHD Numeric Observation Profile

The consumer of this profile does not need to concern itself with the mapping complexities or the PHD-related entry for the Observation.identifier which is used by the uploader to prevent data duplication. There are no extensions introduced by this profile except for the HL7 gateway extension so the resource is consumable by any reader that understands the Observation resource. The following table summarizes the elements used describing the measurement:

Measurement item element Additional Information
measurement type Observation.code.coding.code There shall be one coding element using the MDC coding system
If a vital sign, there will be an additional coding element using one of the LOINC ‘magic’ codes.
measurement value Observation.valueQuantity.value Value has precision of original measurement
measurement units Observation.valueQuantity.code Uses UCUM coding system.
error Observation.dataAbsentReason Contains error code. If present no Observation.valueQuantity is present
time stamp Observation.dateTimeEffective

Observation.period		 If the measurement is a point in time.

If the measurement has a duration.
coincident time stamp Observation.derivedFrom Points to Observation following the Coincident Time Stamp Observation profile. For time quality auditing purposes. Not present if the sensor provides NO time stamp
related measurement Observation.derivedFrom Points to a PHD Observation that is related to this Observation such as a cardio session. Not present if the device did not reference an additional measurement.
additional descriptions Observation.component If a component element exists it contains additional information about the measurement
patient Observation.subject Points to the Patient resource
sensor device Observation.device Points to the Device resource

The Other Profiles