2.2 Component/Analyte

The first main part consists of three subparts: (1) the principal name (e.g., the name of the Analyte or the measurement); (2) the Challenge or provocation, if relevant, including the time delay, substance of challenge, amount administered, and route of administration; and (3) any standardization or Adjustment.

The three subparts of the first part follow this syntax:

<[analyte].[subclass].[sub-subclass]> ^
<[time delay] post [amount] [substance] [route])> ^
<adjustment>

In the above syntax, the carat (^) is a required delimiter and the “dot” (.) separates the Analyte name from its subspecies.

This convention also implies that dots (.) and carats (^) cannot be a formal part of any of the words that are connected by these delimiters.

These subparts are described in greater detail below, Sections 2.2.1 through 2.2.3.

2.2.1 Analyte name (1st subpart)

The first subpart names the Analyte, including any relevant sub-classifications, separated from the main Analyte name by dots.

2.2.1.1 Analyte/subclass

The principal name (the first subpart) can be divided further by subclass (e.g., Calcium by itself is one Component, Calcium.ionized names another test that measures a subclass of calcium). Subclasses are separated by dots. Examples of common subclasses include: bound, free, and bioavailable; ionized and non-ionized; glycated; glucuronidated and non-glucuronidated; IgA, IgD, IgE, IgG, and IgM as modifiers indicating the subspecies of antibodies. Note that bioavailable is distinguished from free by including both free and partially bound moieties.

If the antibody is from a particular subclass of antibodies, specify the type of immunoglobulin (IgM, IgG, IgA, or IgD), e.g., Hepatitis A virus Ab.IgG, Hepatitis A virus Ab.IgM. If more than one subclass of immunoglobulin is included in the measurement, all are listed in the subclass, e.g., Mumps virus Ab.IgG+IgM with a plus sign (+) to separate the subspecies. There should be no spaces between the plus sign and the words it connects.

If two or more constituents are measured as one quantity, each constituent should be named in the Component separated by a plus sign, e.g., Cyclosporine+metabolites or Human papilloma virus 16+18+31+33+35+45+51+52+56 DNA.

If multiple Analytes are measured separately, the Analytes are separated by an ampersand (&) surrounded by spaces. Two cases that use the ampersand convention are the names of panel terms and impression terms.

The naming of panel terms is described more completely in Section 8, but here we describe its use of ampersand. The enumerated child elements of a panel are each measured individually, so we often use ampersand in the name of the parent term (the panel term), e.g., ABO & Rh group panel. This particular example of ABO & Rh group also illustrates how panel terms using ampersand are different than an observation term with ampersand. The ABO & Rh group panel is linked to two separate observation codes, one for ABO and another for Rh group, that each carries its own result. An ABO & Rh group observation term would carry a combined (but separately measured) result (e.g. A positive). Either term could be used in ordering, depending on the reporting approach.

Impression terms may also use ampersand, for example, Hepatitis A virus Ab.IgM & total impression. In the case of the Hepatitis antibody impression, both the IgM antibody and the total impression are described separately.

In some cases, panel or impression Components contain both a plus sign (+) and an ampersand (&), for example, Human papilloma virus 16 & 18 & 31+33+35+39+45+51+52+56+58+59+66+68 DNA impression. In this example, the HPV 16 and HPV 18 impressions are both described separately, as is the impression for the group HPV 31+33+35+39+45+51+52+56+58+59+66+68, which is measured as a single quantity.

2.2.1.2 Divisor

Some Analytes contain a Divisor, which represents the denominator of a result that is expressed as a fraction or ratio. The numerator does not have a separate name because by default the Analyte is the numerator for all terms. In Analytes that do have a Divisor, the numerator is separated from the Divisor by a slash (/). For example, in the Analyte Albumin/Protein.total, the numerator is Albumin and the Divisor is Protein.total, so that the overall Analyte represents albumin as a fraction of the total protein. Similarly, Albumin/Creatinine represents the ratio of albumin to creatinine. Note that in the former case, the Property would be a type of Fraction, since albumin is a type of protein (i.e., albumin represents a fraction of total protein), whereas in the latter, the Property would be a type of Ratio, because the amount of albumin is being compared to the amount of creatinine, but neither of them is a parent compound of the other.

2.2.2 Challenge test (2nd subpart)

The second subpart contains information necessary to interpret “challenge” (or loading or tolerance) tests. Variables that report the result of a measurement taken a certain amount of time post challenge (e.g., glucose after an oral glucose tolerance test) must be distinguished according to the challenge and the time post challenge. Thus, the Challenge subpart has a substructure that identifies the time interval or time difference and the challenge, using the following syntax, where the word “post” (or base line) is required.

<time delay> “post” <challenge>

where the challenge can be further characterized as

<amount given> <substance/treatment given> <route given>

An example of a Challenge that used all parts would be: Aldosterone^1H post 25 mg captopril PO

The time difference follows the syntax: n\<S|M|H|D|W> where n is a number (possibly a decimal); S denotes seconds; M denotes minutes; H denotes hours; D denotes days; and W denotes weeks. The time delay can be preceded by a ‘greater than’ (>) sign, e.g., >4H. Table 4 lists some possible values for time difference, but any time specification that follows the above syntax would be legal.

In addition to specifying a time elapsed since challenge, the time delay slot can be used to name a clock time when the measurement was taken, e.g., Glucose^10 AM specimen, or to specify the ordering of specimens, e.g., ^1st specimen, ^2nd specimen. Use this syntax to indicate pre- and post-immunization specimens, acute and convalescent specimens, or a series of specimens for which no more detailed information is available.

Table 4a: Example Time Delay Post Challenge

Table 4b: N minutes/hours/days/weeks/months/etc. after challenge begun

The second subpart is also used to describe measurements taken at a specified point after the beginning of an ongoing treatment, such as peritoneal dialysis, e.g., Creatinine^12H post peritoneal dialysis. More generally, this syntax can be used to indicate that observations were recorded, e.g., ^post partum, ^postoperative, or ^post EDTA therapy.

The syntax of the second subpart can be specified in various ways to indicate Challenges of greater or lesser specificity, corresponding to the amount of detail that the laboratory knows about the challenge specimen.

Examples of the range of possibilities include:

Table 5: Example Challenge Subparts

We denote the route of the challenge by HL7 Version 2.3 “abbreviations for medication routes” (Table 6). An oral route of administration would be denoted by PO,[[^20]] an intravenous route by IV.

Table 6: Example Route Abbreviations for Challenge Part (from HL7 v.2.3, Chapter 4)

Examples:

Glucose^30M post 100 g glucose PO:MCnc:Pt:Ser/Plas:Qn:

Gentamicin^trough:MCnc:Pt:Ser/Plas:Qn:

For drug peak (obtained at a time presumed to reflect the highest concentration) and trough (obtained at a time presumed to reflect the lowest concentration) measures, the nature of the substance loaded is the same as the Analyte name, and need not be included.

2.2.2.1 Reporting the baseline measure as part of a Challenge test

Through LOINC release 2.52, we have defined one baseline term for different Challenge batteries when the Challenge is given by the same dose and route. For example, we define one baseline serum glucose for the 100 gm oral glucose tolerance test regardless of the number of separate measurements defined in the battery:

Glucose^pre 100 g glucose PO

A laboratory could use this same test identifier to identify the baseline result of a two-hour glucose tolerance and a three-hour glucose tolerance, for example.

However, the number and variety of challenge terms users have been requesting are growing rapidly. It now appears impractical to create a baseline term for every dose and route combination. Furthermore, baseline measurements are not affected by the subsequent challenge and could in principle be reported simply as the “unadorned” measurement with no named relation to a coming Challenge. Therefore, we have created generic baseline “pre challenge” terms, for example, Glucose^pre XXX challenge. For these terms, the specifics of the challenge would be reported elsewhere.

2.2.2.2 Physiologic challenges

Some challenges are defined in terms of a physiologic stress, not a dose of a chemical substance. The LOINC names currently cover calorie fasts (no calorie intake), exercise, and fluid restrictions. These Challenges are denoted by codes given in Table 7.

In the case of such Challenges, the syntax also includes the duration of the Challenge. For example:

post <duration><physiologic challenge>
Triglyceride^post 12H CFst

Table 7: Example Nature of Challenge

The naming structure is an exact analogous structure to that of chemical challenges. A test for glucose after 12 hours of an energy fast would be represented as:

Glucose^post 12H CFst:MCnc:Pt:Ser/Plas:Qn:

A test for osmolality after a 12-hour fluid restriction would be:

Osmolality^post 12H FFst:Osmol:Pt:Urine:Qn:

A test for triglyceride after 12-hour energy fast would be:

Triglyceride^post 12H CFst:MCnc:Pt:Ser/Plas:Qn:

Two durations can appear in one specification, for example:

Cortisol^1.5H post 0.05-0.15 U insulin/kg IV post 12H CFst:MCnc:Pt:Ser/Plas:Qn:

Our rules for naming challenge tests work well only when there is a single intervention followed by a test for one or more Components over time. Complex challenge tests involving more than one intervention or complicated sampling techniques need a unique name, but the name may not provide a complete description of all of the test parameters.

2.2.2.3 Reporting characteristics of challenge as separate observations

Because we cannot anticipate every type of challenge and route of administration, and because some challenge tests have no usual dose, some challenge tests will not contain a dose. Challenge observations that do not include a specific dose in the name have the word “dose” where a numeric dose would otherwise appear. The general form is:

<analyte>^<time> post dose <route>

Examples:

Glucose^1H post dose insulin IV:MCnc:Pt:Ser/Plas:Qn:

The actual dose might then be sent as a comment or as a separate “test” that carries the dose as its value. To accommodate laboratories that wish to transmit the relevant challenge dose as a separate observation, we also define separate test names (and codes) for reporting such doses. This dose could then be sent by the reporting service as a separate result in a separate OBX segment.

The name of the observation that identifies the value of the dose would have the form:

<drug or challenge substance>: <time> post dose <challenge substance>

Examples:

Glucose.PO:Mass:Pt:Dose:Qn:

Gentamicin:Mass:Pt:Dose:Qn:

Thus we distinguish a drug concentration from the drug dose by means of the System (sample), 4th part, of the test name (see Section 2.5). You can find the observations that carry the dose of drugs or challenges grouped in the class DRUGDOSE in the LOINC database. This approach has the advantages of parsimony and practicality. It also provides an observation ID for the piece of information that must be transmitted along with the request for the observation.

Another example would be:

Oxygen:PPres:Pt:BldA:Qn:

Oxygen inhaled:VRat:Pt:Inhl gas:Qn:

Example Units: liters/minute or milliliters/second

Oxygen inhaled mechanism:Type:Pt:Dose:Nom:

Comment: to report kind of delivery mechanism, e.g. nasal cannula

An analogous approach is used for reporting many kinds of associated variables when the variables are not conventionally embedded in the name. We take this approach in part because there are too many levels of the variables and it is not feasible to represent them all.

2.2.2.4 Generic Challenge specifications

We allow for a range of specificity regarding Challenges from fully specified to very generic.

Some Challenges will be specified fully as described above, e.g., ^30M post 100 g glucose PO. We will also include: challenges without the amount specified, e.g., ^30M post dose glucose; those that specify a time elapsed but not a particular challenge, e.g., ^1H post XXX challenge; those that do not specify the exact time but provide ordering information, e.g., ^2nd specimen post XXX challenge; or even more generic, ^post XXX challenge. These latter variants are needed to accommodate challenges that do not fit any common protocol, or referrals to reference laboratories where the study protocol is not reported.

2.2.2.5 Acute and convalescent, pre and post immunization

To assess the efficacy of immunizations, antibody levels are measured before and after the immunization; similarly, evidence for acute infection is obtained by assessing acute and convalescent screens. Both of these cases are reported with the 1st specimen, 2nd specimen syntax, for example:

Acute specimen, 1st specimen, pre-immunization specimen:

Streptococcus pneumoniae Ab.IgG^1st specimen:ACnc:Pt:Ser:Qn:

Convalescent specimen, 2nd specimen, post-immunization specimen:

Streptococcus pneumoniae Ab.IgG^2nd specimen:ACnc:Pt:Ser:Qn:

2.2.3 Adjustments/corrections (3rd subpart)

The third subpart of the data element contains calculations that adjust or correct some measured value. We use this subpart to distinguish corrected or adjusted values from the uncorrected measurement, e.g., corrected cell counts from the raw cell counts. Since these attributes are unique to each measurement, they will be short phrases of text rather than a controlled vocabulary to define the content of the third subpart. However when defined, such a test will have a unique LOINC code and the meaning will be fixed by the text in the third part.

Examples:

Calcium.ionized^^adjusted to pH 7.4:SCnc:Pt:Ser/Plas:Qn:

Leukocytes^^corrected for nucleated erythrocytes:NCnc:Pt:Bld:Qn:

2.2.4 Distinguishing multiple values for any test via the test name (4th subpart)

HL7 messaging allows for multiple results for one observation. However, some systems cannot distinguish separate answers per observation, so they made the test names like organism 1, organism 2 or substance 1, substance 2 to report multiple organisms or substances identified in samples. We do not encourage this type of reporting because that distinction can more clearly be accomplished by using one test name (e.g., organism identified) and the HL7 sub ID to distinguish the multiple organisms/substances. However, we have created a few terms to accommodate systems that bind the distinction into their test names. The fourth subpart of the Component name will allow reporting of repeat observations taken at the same time and/or on the same specimen.

Example:

Bacteria identified^^^2:Prid:Pt:Stool:Nom:Culture

[[^20]]: In the United States, PO (an abbreviation for per ora) is used to identify medications taken by mouth.