4 - Clinical observations and measures

4.1 Introduction

For most of the measures we include separate observations for summary data, e.g., shift and 24-hour urine output totals. We also provide varying degrees of pre-coordination for the observation, the body site at which it was obtained, and the method. For example, a cardiac output based on the Fick method is distinguished from a cardiac output computed from 2D cardiac echo data.

Physiologic measures are often monitored continuously over time and the instrument reports summary “statistics” over that reporting period. For vital signs, these can include minimum, maximum, and mean value over a time period. For intake and output, the total is the summary statistic usually reported. When we address measures taken over time, we usually include 1-hour, 8-hour, 10-hour, 12-hour, and 24-hour intervals to cover the varying lengths of work shifts within and across institutions. The LOINC names of these correspond to the form of a 24-hour urine specimen. The times are recorded in the duration (third part) of the name.

The parts of clinical measurement names are largely the same as for laboratory measures, with some subtle differences that are detailed below.

  • Parts 2, 3, 5 and 6 (type of Property, Time Aspect, Scale, and Method) correspond exactly in meaning between laboratory and clinical LOINC codes.
  • System: Part 4, body System, has the same general meaning for clinical and laboratory measures, but whereas in the case of laboratory tests the System usually identifies a fluid and a body compartment by implication (e.g., serum, cerebral spinal fluid), for clinical terms, the System is usually a body part (e.g., chest), organ (e.g., heart), or part of an organ (e.g., heart.ventricle). In some cases the System may be an instrument or device attached to the system (e.g., OB ultrasound imaging device).
  • Component: In the case of laboratory test observations, the Component (part 1) usually identifies some chemical moiety that is distributed in the System (Glucose, or HIV 1 Ab). In the case of clinical terms, the Component usually identifies a particular projection of a three- or four-dimensional space to a measure of a particular feature (e.g., QRS interval, Intrachamber.systolic) of a time changing measure (Heart.ventricle.left.outflow tract). In addition, the Component is used to distinguish the various ranges or inflections of a physiologic tracing, or to define precisely the section in three-dimensional space in which an area or range is being measured. The Component includes such things as the special kinds of length (e.g., circumference, diameter, or radius) when length is the Property, and the specific level and axis on which a measurement of a body part is taken, e.g., circumference taken at the nipple line. The Component should remove all ambiguity as to what projection or axis or specific sub-time frame is being measured. So if one is measuring the diameter of the kidney, the System would have to specify kidney.right (or kidney.left), and the Component would identify the axis and level at which the diameter was measured (e.g., cross-sectional at level of pelvis). For a measure of chest circumference the System is chest, the Component is circumference at nipple line, and the Property is length. Areas, lengths, and volumes of organs all have to be specified enough in the Component to distinguish a particular area or length that is being measured. When a measure changes over some cycle (e.g., inspiration, expiration, diastole, and systole), then that should also be specified in the Component. (Duration is used to identify the duration of an overall study.)

For most clinical measurements, the Component is an attribute of a patient or an organ system within a patient. However, attributes of non-patient systems are also often of interest. For example, we might want to know the class of instrument used to obtain the measurement: i.e., the vendor model number or institutional inventory number of an endoscopy. Such identification numbers have a Property of ID. Infection control might want the latter reported in order to track nosocomial infections.

When attributes of an instrument or device are being reported, the System is the name of the instrument. The same is true when we report characteristics of tubes used to move fluid in and out of body cavities. For example, we might want to report the size and type of a nasogastric tube.

Table 20: Example subjects covered in clinical LOINC

Blood pressure (systolic, diastolic, and mean)
Body measurements
Body weight (and measures used to estimate ideal body weight)
Cardiac ultrasound
Cardiac output, resistance, stroke work, ejection, fraction, etc.
Circumference of chest, thighs, legs
Critical care measures
Electrocardiographic measures
Emergency department case reports (CDC DEEDS)
Gastroenterology endoscopy
Heart rate (and character of the pulse wave)
Intake and output
Major headings in operative note
Major headings in discharge summary
Major headings of history and physical
Obstetric ultrasound imaging
Ophthalmology measurements
Pathology protocols
Pulmonary ventilator management
Radiology reports
Respiratory rate
Standardized survey instruments
Urology ultrasound imaging

To accommodate the special dimensions of clinical observations we have introduced new options for the kind of Property. The new kinds of Property are what you might expect from the new kinds of dimensions being measured (e.g., resistance, voltage, work per beat). However, we have also introduced three important new properties:

  • Anat: Anatomic is a special case of Prid that identifies anatomic sites.
  • Imp: Impression is a diagnostic statement, always an interpretation or abstraction of some other observation (a series of test results, an image, or a total patient), and almost always generated by a professional. (We could also consider the EKG cart's automated diagnoses as impressions.) Impressions are used in laboratory medicine as well as clinical medicine, so you will see them appearing there as well.
  • Find: Finding is an atomic clinical observation, not a summary statement as an impression. Physical review of systems and other such observations have a Property of Find. These may have a Scale of Nom for coded findings, Nar for findings reported in narrative text or Ord for ordinal findings.
  • Hx: Terms representing patient or family history concepts originally had Components that began with “History of” and were assigned the Find Property. As of LOINC version 2.56, these terms were updated to remove “History of” from the Component and change the Property to Hx, which is exactly what this Property represents.

In clinical measures, super systems (the second subpart of the System component) may be required. For example, we distinguish head measures of a patient versus a fetus as follows:


4.2 Atomic versus molecular (pre-coordinated names)

With clinical terms we almost always have two ways of reporting. Using the first, we can report an observation by reporting a number of atomic variables which together fully describe the observation. For example, we have the following atomic observations for circumference measures. These variables let us deal with all of the unique kinds of circumferences for which we have not yet defined a pre-coordinated term. The following table shows examples of pre-coordinated names.

Table 21: Examples of Pre-Coordinated Names

Code Description
Circumference:Len:Pt:XXX:Qn The actual measure of some circumference
Circumference site:Anat:Pt:*:Nom Identifies the body part measured (specifies the System)
Circumference method:Type:Pt:XXX:Nom:* Identifies the measuring technique used to obtain the circumference (answers = tape measure, derived, imaging)

We also provide pre-coordinated terms that combine some of the atomic variables into one LOINC code. For example, we have:

8279-2 Circumference.at nipple line:Len:Pt:Chest:Qn


8293-3 Circumference^inspiration:Len:Pt:Chest:Qn

which provide more specificity and permit the key components of the measure to be expressed as one variable as is the convention in many clinical systems. We call these pre-coordinated codes “molecular” variables.

Within the LOINC database molecular variables will vary with respect to how many atomic components are aggregated. As is true in some laboratory areas, methods often are not included as part of a name, nor are they always reported. The most common molecular aggregation is between functional measure and a particular site of measurement (e.g., the many different intravascular sites for blood pressure measurements). But in some cases, the molecular variables represent combinations of specific measures and particular methods (e.g., the cardiac output measures). Please note that most molecular variables could also be accompanied by one or more atomic measures to provide special information about the measure, e.g., special circumstances of the measure, or the vendor model number or institutional inventory number of the measuring instrument.

When we have a variable that really reports what would have been contained in the name in a fully pre-coordinated term, we will place an asterisk in the part that will be reported as a value. For example, a variable that is used to report the anatomic site as an atomic variable, would have an asterisk (*) in the System part of the name. The variable used to report the method of a particular measure would have an asterisk (*) in the Method part of the name.

4.3 Radiology reports

As of the December 2017 LOINC release, we have completed updating all of our radiology content according to the LOINC/RadLex Unified Model, which was developed through our collaboration with the Radiological Society of North America (RSNA).

You can find information about the unified model at the end of this document, in the LOINC/RSNA Radiology Playbook User Guide.

The following table provides a reference for how the attributes in the Unified Model correspond to the primary LOINC Parts.

Table 22: Relationship of primary LOINC Parts to Radiology attributes

Primary Part Radiology Attribute
Component 1st part (Analyte) View, Guidance, Reason for Exam
Component 2nd part (Challenge) Timing, Maneuver, Pharmaceutical
System Anatomy, Subject
Method Modality

4.4 Tumor registry

In collaboration with North American Association of Central Cancer Registries, Inc (NAACCR, Inc), we have developed a set of LOINC codes that can be used to communicate tumor registry variables from clinical institutions to tumor registries and among tumor registries. These LOINC terms map to the content of NAACCR data set, and include variables for such things as the hospital at which the tumor was first diagnosed, the primary anatomic site of the tumor, it size, its degree of spread at the time of diagnoses, and a host of other variables of interest to the tumor registries. The NAACCR data set and other cancer-related demographics are identified by the Class TUMRRGT.

The NAACCR standards and an implementation guide for transmitting these LOINC tumor registry variables within HL7 messages are available from the NAACCR website (http://naaccr.org).

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