The Method by which the test was performed is the sixth part of the test name. Methods need only be expressed as part of the name when they provide a distinction between tests that measure the same Component (Analyte) but which have different clinical significance or have a different clinical reference ranges. For instance, whole blood glucose tested with a test strip might be distinguished in the Method field.
A non-exhaustive list of example Methods are listed in Table 13. The complete set of active LOINC Methods is available in the LOINC Part File and can be identified because they contain a PartTypeName of METHOD. Further, many Methods have descriptions that can be found on the Details Page for that Part. For example, see the details page for LP70657-9 RPR.
Laboratories do not include the Method as part of the name for most common chemical and hematological tests. They often need the freedom to choose the instrument according to time of day, urgency of the request for service, availability of the instruments and so on, even though the instruments may employ different methods. The laboratories then adjust each of the “interchangeable” instruments to produce equivalent results even though the instruments may use different methods. Therefore, we do not want to distinguish too finely on the basis of methods. When a LOINC term does include a Method, it usually describes a type or class of method and does not make fine-grained distinctions except in special cases.
Though Method is rarely significant for many chemical and hematological tests, it is often important to immunochemical/serology testing, because the sensitivity and specificity of some tests varies greatly with the Method. For this reason, you will commonly see Methods included in microbiology tests and coagulation tests within the LOINC database.
This does not mean that detailed information about the Method is irrelevant, but that it is not always useful or practical to bind it to the test name. It is an essential element of the internal quality assurance of laboratories and there are fields for reporting other details about the Method in HL7 and CEN TC251 test result messages.
Table 13: Laboratory Method Type Abbreviations
| Method* | Abbr. | Comment |
|---|---|---|
| Agglutination | Aggl | |
| Cell binding assay immunofluorescent assay | CBA IFA | Cell binding assays are performed using cells that are engineered to only express the antigen of interest, which increases their specificity compared to traditional immunofluorescent assays. |
| Coagulation Assay | Coag | To distinguish coagulation assays based on clotting methods that test function/activity from Immune methods that detect the presence of clotting factors and may or may not be functional assays. |
| Complement-dependent Cytotoxicity | CDC | |
| Complement Fixation | Comp fix | |
| Cytology Stain | Cyto stain | The staining method used for pap smears, fine needle aspirates and other cell stains. |
| DNA Nucleic Acid Probe | Probe | See Section 2.7.1 for more information about probes. |
| Chromogenic/Enzymatic Assay | Chromo | To distinguish coagulation assays based on chromogenic (enzymatic) activity. |
| Immunoassay | IA | Encompasses all immunoassays with a few exceptions, including Immune Blot and Immune Fluorescence, which were created based on historic usage. |
| Flocculation Assay | Floc | |
| Hemagglutination Inhibition | HAI | |
| Hemagglutination | HA | Encompasses direct and indirect |
| Immune Blot | IB | Applies to techniques that include electrophoretic or chromatographic separation such that position (size) of the band is part of the assessment |
| Immune Fluorescence | IF | Encompasses DFA, IFA, FA. Usually applies to cells and smears examined microscopically so that both the “where” and the “what” can be assessed, but can also be used on fluids in a way similar to ELISA. Does not include Cell binding assays (see CBA IFA above). |
| Latex Agglutination | LA | |
| Leukocyte Histamine Release | LHR | |
| Line blot | Line blot | A membrane strip pre-coated with a specific set of antigens in parallel lines that are incubated with antibodies in order to detect the targets of interest. |
| Minimum Inhibitory Concentration | MIC | Antibiotic susceptibilities |
| Minimum Lethal Concentration | MLC | Also called MBC (minimum bactericidal concentration) |
| Molecular Genetics | Molgen | General class of methods used to detect genetic attributes on a molecular basis including RFL, PCR and other methods. |
| Virus Neutralization | Neut | Virus neutralization tests, which traditionally relies on live-virus based assays. |
| Pseudovirus Neutralization | pVNT | Pseudovirus-based neutralization tests |
| Radioimmunoassay | RIA | |
| Rapid Plasma Reagin | RPR | Microscopic flocculation test, using cardiolipin-lecithin-cholesterol antigen with carbon particles. |
| Serum Bacterial Titer | SBT | Determines the serum dilution that is capable of killing microorganisms. |
| Rapid Plasma Reagin | RPR | Microscopic flocculation test, using cardiolipin-lecithin-cholesterol antigen with carbon particles. |
| Vertical Auto Profile | VAP | Developed by Atherotech, Inc. |
| Visual Count | VC | |
| Venereal Disease Research Laboratory | VDRL | Microscopic flocculation test |
2.7.1 Methods for identifying nucleic acids
We distinguish Methods that detect nucleic acid based on two aspects of the assay: whether or not the target nucleic acid is amplified (copied), and how it is detected. We are still working on determining what the most important distinctions are in the variety of nucleic acid detection methods that are used, and may update our Methods to reflect these distinctions in the future. As of the 2.63 release, however, we use the following Methods:
Probe-based detection without amplification (Probe)
Definition: A hybridization probe is a typically a short nucleic acid segment that binds to a complementary nucleic acid sequence that is specific to the target of interest. The probe is typically attached to signaling molecule in such a way that a signal is only generated when the probe binds to the target nucleic acid. In LOINC, the Probe method is used for assays that do not include either a nucleic acid amplification or a signal enhancement step.
Target amplification followed by probe-based detection (Probe.amp.tar)
Definition: The Probe.amp.tar Method in LOINC is used for assays that include a nucleic acid amplification step, in which many copies of the nucleic acid sequence(s) of interest are made, followed by detection of the target nucleic acid of interest using a hybridization probe. Nucleic acid amplification can be done using different techniques such as polymerase chain reaction (PCR). The primary difference between the Probe.amp.tar and Non-probe.amp.tar Methods is the technique used for target nucleic acid detection. Note that for historical reasons, this Method also includes older techniques for identifying PCR target amplification products, such as gel separation and staining to identify the fragments based on their expected sizes.
The Probe.amp.tar Method is represented as NAA+probe in the Short Name and NAA with probe detection in the Long Common Name.
Signal amplification followed by probe-based detection (Probe.amp.sig)
Definition: Probe with signal amplification is a lab method that uses a hybridization probe, which is a typically a short nucleic acid segment that binds to a complementary nucleic acid sequence that is specific to the target of interest, followed by a signal enhancement step, in which the signal that is generated when the probe binds to the target sequence is multiplied so that it is “brighter” and easier to detect. Signal amplification can be done using different techniques, including the branched-chain DNA (bDNA) method. In theory, signal amplification is more sensitive than a probe by itself because it generates a brighter signal per each copy of the target sequence that is present. In LOINC, the Probe.amp.sig method is assigned to codes for assays that do not include a nucleic acid amplification step.
The Probe.amp.sig Method is represented as Probe+sig amp in the Short Name and Probe with signal amplification in the Long Common Name.
Target amplification followed by non-probe based detection (Non-probe.amp.tar)
Definition: The LOINC Non-probe.amp.tar method is used for assays that include a nucleic acid amplification step, in which many copies of the nucleic acid sequence(s) of interest are made, followed by detection of the target nucleic acid of interest using a method other than a hybridization probe, such as melt curve analysis or turbidity measurement. The primary difference between the Probe.amp.tar and Non-probe.amp.tar Methods is the technique used for target nucleic acid detection.
The Non-probe.amp.tar Method is represented as NAA+non-probe in the Short Name and NAA with non-probe detection in the Long Common Name.
Historical information: In LOINC version 2.54, we added a new Method for target amplification with melt curve analysis (Melt.amp.tar) to distinguish assays that use melt curves rather than probes for analyte detection. For version 2.56, we replaced Melt.amp.tar with a more encompassing non-probe based Method (Non-probe.amp.tar) that is used for PCR assays with non-probe based detection technology, including melt curve analysis, and which still distinguishes from probe-based assays (Probe.amp.tar). The Method for the terms originally created with the Melt.amp.tar Method was updated to Non-probe.amp.tar for the 2.56 release, and Melt.amp.tar is no longer in use.
Examples of specific techniques and their corresponding Methods
The tables below describe specific techniques that are included in each of the four Methods described above.
Table 14a: Examples of methodologies that are included in the Probe Method
| Method Type | Description |
|---|---|
| DNA probe | A fragment of labeled DNA, usually 100–1000 bases long, which can be used to detect the presence of nucleotide sequences that are complementary to the sequence in the probe. |
| RNA probe | A fragment of labeled RNA, usually 100–1000 bases long, which can be used to detect the presence of nucleotide sequences that are complementary to the sequence in the probe. |
Table 14b: Examples of methodologies that are included in the Probe.amp.tar Method
| Method Type | Description |
|---|---|
| Polymerase chain reaction (PCR) with probe-based target detection (e.g., conventional PCR, real-time PCR) | A technique that requires repeated cycles of heating and cooling to double the targeted nucleic acid sequence with each cycle. In conventional PCR, after the amplification is complete, the target is detected using a labeled probe; in real-time PCR, the target is detected using probes during the amplification process. |
| PCR with target detection based on gel separation and staining of PCR products | PCR followed by gel separation and staining to identify the fragments based on their expected sizes. This older technique for identifying PCR amplification products is included in Probe.amp.tar for historical reasons. |
| Transcription mediated amplification (TMA) | An isothermal technique that uses RNA polymerase and reverse transcriptase enzymes to amplify the targeted nucleic acid sequence. |
| Nucleic acid sequence based analysis (NASBA) | An isothermal transcription-based amplification method specifically designed for the detection of RNA targets. |
| Strand displacement amplification (SDA) | An isothermal amplification technique that relies on a strand-displacing DNA polymerase. |
| Hybridization protection assay (HPA) | A chemiluminescent-based detection assay that uses specific oligonucleotide probes labeled with an acridinium ester (AE) enzyme that emits a chemiluminescent signal when the probe binds to the RNA target. |
Table 14c: Examples of methodologies that are included in the Probe.amp.sig Method
| Method Type | Description |
|---|---|
| Hybridization protection assay (HPA) | See description above. |
| Branched chain DNA (bDNA) | Involves a series of hybridization reactions for the detection of a nucleic acid sequence. bDNA is commonly used for the diagnosis and monitoring of viral and bacterial infections. |
| Hybrid capture | Involves nucleic acid hybridization and microplate chemiluminescent detection. A microplate is coated with tagged antibodies that bind nucleic acid hybrids, capturing the hybrid molecules to the microplate. |
Table 14d: Examples of methodologies that are included in the Non-probe.amp.tar Method
| Method Type | Description |
|---|---|
| Target amplification (e.g., using conventional PCR) with melt curve analysis | Amplification of a targeted nucleic acid sequence using a technique such as conventional PCR, followed by target detection by melt-curve analysis. DNA-binding dyes, such as SYBR Green I, are used to produce a melt-curve profile. The profile is based on the total fluorescence generated from the DNA-binding dye as it binds to melting double-stranded DNA as temperature changes. |
| Loop-mediated isothermal amplification (LAMP) | An isothermal nucleic acid amplification technique that uses 4-6 primers recognizing 6-8 distinct regions of target DNA. Synthesis is initiated by a strand-displacing DNA polymerase and two of the primers form loop structures to facilitate subsequent rounds of amplification. |
Note
The items in the first column of the above table are not meant to be used as Methods in LOINC terms.
2.7.2 Immune assays
Immune assays in the LOINC world include a large swath of tests. We have historically lumped together immune assays that detect the linking of antigens and antibodies via special signaling mechanisms, such as EIA, ELISA, chemiluminescence and other similar tests that produce one measure (quantitative or qualitative) of the analyte of interest. We thought of this class of tests as “EIA-like” and in the absence of an existing short acronym to describe their constituents, we borrowed EIA to provide this meaning in the Short Name and used Immunoassay in the Long Common Name to signal that this method type was not limited to pure EIA tests. In LOINC version 2.56, we changed the name of the EIA Method to IA (and EIA.rapid to IA.rapid), in order to mitigate some of the confusion regarding the EIA name. The Long Common Name will continue to use Immunoassay as it always has, and the Short Name will use IA rather than EIA.
Some immunologic tests have always had their own Method type and were never lumped in the category of EIA-Immune assays described above. Immune blot (IB) tests, immune diffusion and immune based flow cytometry (FC) tests have always had specific method names because they are different in that they usually yield multiple related observations.
Immune fluorescence tests (IFA, DFA and ACIF) also have had their own Method type, namely IF, because they can provide information about the presence or amount of a target analyte AND its location (or pattern) on a smear, tissue slice or cell. Immunofluorescent cell binding assays, which use cells that are engineered to express a single antigen of interest, use the Method CBA IFA. LOINC has also assigned distinct method types to some other immunologic tests including VDRL, Latex fixation, and other kinds of agglutination tests because these were their historic names or they had specialized uses or limits.
We classify peroxidase and all other non-IF immune stains of tissue under the Method category immune stain.
2.7.3 Immunoblot and Line blot Methods
LOINC has two different Methods for Immunoblot (IB) and Line blot. IB is used in cellular and molecular biology to identify a specific protein in a complex mixture extracted from cells. Gel electrophoresis separates polypeptide chains (subunits) into bands according to their molecular weight. The bands are transferred onto a membrane and incubated with a primary and secondary antibody to visualize the target subunits. The Line blot Method is similar in that it utilizes membrane strips that are pre-coated with a specific set of antigens in parallel lines that are incubated with antibodies in order to detect the targets of interest. However, LOINC distinguishes the two Methods based on when the electrophoretic/chromatographic separation occurs. In IB, the separation occurs in the testing laboratory, whereas in Line blot, it occurs during the manufacturing step and not in the testing laboratory.
2.7.4 Coagulation
We distinguish among three kinds of coagulation methods: those that measure the coagulation activity (Coag), those that measure the coagulation factor via enzyme rate (Chromo or enzymatic), and those that measure the amount of the coagulant protein, not its activity. The Method that measures the amount of protein was called Imm until the 2.58 release, for which it was renamed IA to be consistent across laboratory classes.
2.7.5 Stains
We provide very detailed distinctions among various tissue stains, naming them in full. Stain methods that are modifications of a basic method are named using a \
Methenamine silver stain.Jones2.7.6 Substrates used to measure enzyme activity
For tests that are measuring enzyme activity using various substrates, the name of the enzyme or enzyme group will be the Component and the substrate will be the Method:
Mitochondrial respiratory chain enzymes: CCnt: Pt: Fibroblasts: Qn: 1-14C-glutamate substrate2.7.7 “Detection limit” Methods
In specific instances, including viral load testing, urine albumin measurement and certain hormones (e.g., thyrotropin), we have LOINC codes where the Method value is the detection limit for the test. These were primarily created based on industry requests to differentiate tests that have at least an order of magnitude (10x) difference in detection thresholds, because this detection limit information was deemed more important than the specific laboratory method that was used. For example, we have codes for urine albumin with the Method Detection limit <= 20 mg/L and Detection limit <= 1 mg/L, and we also have thyrotropin terms with Method Detection limit <= 0.05 mIU/L and Detection limit <= 0.005 mIU/L. In some cases, the detection limit values are not round numbers, e.g., Detection limit <= 3.47 pmol/L. This seemingly odd value of 3.47 pmol/L is the molar equivalent of 1.0 ng/dL.
Based on discussion at the June 2018 Laboratory LOINC Committee meeting, LOINC terms that specify a detection limit in the Method are no longer recommended for use, except in a select number of use cases such as thyrotropin and urine albumin. In general, we will not create new terms with such Methods because the detection limit is not actually a Method but rather a measure of the sensitivity of the test. Instead, we recommend using a more generic code, such as a term with Probe.amp.tar as the Method for a viral load, and reporting the detection limit separately using LOINC 87706-8 Laboratory device Detection limit.
2.7.8 “Confirm” Method outside of Drug/Tox
In a few special cases outside of Drug/Tox, we have codes with the Method Confirm. In each of these instances, the fact that the specific instance of the result is a confirmatory result is deemed more important than the specific laboratory method used to obtain the result. Two such cases include ABO & Rh group typing, and Hepatitis B virus surface antigen testing in pregnant women.
2.7.9 Special issues with Methods for clinical measures
2.7.9.1 Estimated versus measured values
For some kinds of clinical measures we distinguish the Method Reported from Estimated and Measured. For example, reported body weight is the stated weight from a patient or surrogate. Estimated body weight is estimated by an observer, and measured would be the body weight as measured on a scale.
2.7.9.2 Oximetry
Use of oximetry as a Method can cause confusion. For details see the Oxygen Saturation Technical Brief at the end of this guide, but briefly, oximetry has several specific types, including pulse oximetry, co-oximetry and heme-oximetry. Unfortunately, at one time the word “oximetry” was used interchangeably with “pulse oximetry,” which created confusion in LOINC because we have one Method called oximetry and another called pulse oximetry. To avoid ambiguity, as of version 2.54 we deprecated most of the terms with oximetry as the Method, and moving forward we will continue to review the ones that are remaining and create new terms with the Method pulse oximetry as needed.
2.7.10 Imaging studies
We distinguish among the major imaging modalities for most measures derived from such imaging studies (e.g., cardiac outputs from a MUGA scan, angiography, 2D Echo, Doppler, etc.).
2.7.10.1 Methods that include imaging modality and calculation
In some cases, the Method includes two concepts: the imaging modality and the method of calculation for the specific measure. Through LOINC version 2.50 we used the pattern \
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