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LOINC Reference

Free reference guide: LOINC Reference

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About LOINC Reference

The LOINC Reference is a searchable guide for Logical Observation Identifiers Names and Codes (LOINC), the international standard for identifying clinical laboratory tests and observations. It covers the LOINC numbering format (e.g., 2345-7), the 6-part axis system (Component, Property, Time, System, Scale, Method), and provides detailed code interpretation examples showing how each axis maps to a specific lab test meaning.

Key clinical laboratory codes are organized by specialty: general chemistry (Glucose 2345-7, Creatinine 2160-0, BUN 3094-0, Sodium 2951-2, ALT 1742-6), hematology (WBC 6690-2, RBC 789-8, Hemoglobin 718-7, Platelets 777-3), urinalysis (specific gravity 5811-5, pH 5803-2, protein 5804-0), and clinical document codes (discharge summary 18842-5, progress note 11506-3). Panels (CBC 24323-8, CMP 24326-1, BMP 51990-0) and LOINC Groups for semantically related codes are also explained.

The reference also covers LOINC tools and integration: search.loinc.org for online code lookup, RELMA (Regenstrief LOINC Mapping Assistant) for local code mapping, FHIR Observation resource integration with LOINC coding system URI (http://loinc.org), UCUM standard units (mg/dL, mmol/L, IU/L), Answer Lists for ordinal/nominal results, and LOINC versioning/release cycles. Everything runs locally in your browser.

Key Features

  • LOINC 6-part axis system explained: Component, Property (MCnc, SCnc, MFr), Time (Pt, 24H), System (Ser, Bld, Urine), Scale (Qn, Ord, Nom), Method
  • Detailed code interpretation examples: 2345-7 (Glucose), 4548-4 (HbA1c), 718-7 (Hemoglobin) broken down axis by axis
  • Key lab codes organized by specialty: chemistry (Glucose, Creatinine, BUN, Na, K, Cl, ALT), hematology (WBC, RBC, Hgb, Plt), urinalysis, and clinical documents
  • LOINC panels: CBC (24323-8), Comprehensive Metabolic (24326-1), Basic Metabolic (51990-0), Urinalysis (24356-8)
  • FHIR Observation integration with LOINC code system URI, JSON coding examples, and UCUM unit codes
  • RELMA mapping tool overview for mapping local test codes to standard LOINC codes
  • LOINC Groups, Answer Lists (LL360-9 Positive/Negative), versioning (biannual releases), and file format fields
  • 100% browser-based with category filtering and dark mode — no account, no download, completely free

Frequently Asked Questions

What is the LOINC 6-part code system?

Every LOINC code is defined by six axes: 1) Component -- the substance being measured (e.g., Glucose, Hemoglobin). 2) Property -- the measurement type (MCnc = mass concentration, SCnc = substance concentration, MFr = mass fraction). 3) Time -- when the specimen was collected (Pt = point in time, 24H = 24-hour collection). 4) System -- the specimen type (Ser = serum, Bld = blood, Urine, CSF). 5) Scale -- the result type (Qn = quantitative, Ord = ordinal, Nom = nominal). 6) Method -- the test method, used only when it affects interpretation (IA = immunoassay, HPLC, Enzyme).

What does LOINC code 2345-7 mean?

LOINC 2345-7 represents Glucose [Mass/volume] in Serum or Plasma. Broken down: Component = Glucose, Property = MCnc (mass concentration), Time = Pt (point in time), System = Ser/Plas (serum or plasma), Scale = Qn (quantitative), Method = not specified. This is the standard code for a fasting or random blood glucose test reported in mg/dL or g/L. The check digit (7) validates the code number (2345).

What are the most commonly used LOINC codes for clinical chemistry?

Key clinical chemistry LOINC codes include: 2345-7 (Glucose in Serum/Plasma), 2160-0 (Creatinine in Serum/Plasma), 3094-0 (BUN/Urea nitrogen), 2951-2 (Sodium), 2823-3 (Potassium), 2075-0 (Chloride), 1742-6 (ALT/SGPT). These are among the most frequently ordered lab tests worldwide and are essential for any LOINC mapping project in a clinical laboratory information system (LIS).

How do LOINC panels work?

LOINC panels group related individual test codes into a single panel code. Common panels include: 24323-8 (CBC panel - Comprehensive), 24326-1 (Comprehensive Metabolic Panel), 51990-0 (Basic Metabolic Panel), and 24356-8 (Urinalysis Complete Panel). Each panel code contains member codes for individual tests. For example, CBC panel members include WBC (6690-2), RBC (789-8), Hemoglobin (718-7), and Platelets (777-3). Panels simplify ordering and result reporting in electronic health records.

How is LOINC used in FHIR Observation resources?

In HL7 FHIR, LOINC codes are used in the Observation.code element with the system URI "http://loinc.org". A typical Observation JSON includes a coding array with the LOINC code (e.g., "2345-7"), display name ("Glucose [Mass/volume] in Serum or Plasma"), and a valueQuantity with a UCUM unit code (e.g., "mg/dL"). This standardized approach enables semantic interoperability across different electronic health record systems.

What is RELMA and how does it help with LOINC mapping?

RELMA (Regenstrief LOINC Mapping Assistant) is a free desktop tool that helps laboratory professionals map their local test codes to standardized LOINC codes. It provides LOINC code search/browsing, automatic mapping suggestions based on test descriptions, and offline use capability. RELMA is essential for hospitals and labs transitioning to standardized coding for interoperability and regulatory compliance.

What UCUM units are used with LOINC?

LOINC uses UCUM (Unified Code for Units of Measure) for standardized unit representation. Common clinical lab units include: mg/dL (milligrams per deciliter), g/dL (grams per deciliter), mmol/L (millimoles per liter), 10*3/uL (thousands per microliter, for cell counts), % (percent, for HbA1c), and IU/L (international units per liter, for enzyme activity). UCUM codes ensure consistent unit interpretation across systems.

Is this LOINC reference free to use?

Yes, the LOINC Reference is completely free with no usage limits, no account registration, and no software download required. All lookups run locally in your browser, so no data is ever transmitted to any server. It is part of liminfo.com's collection of free online healthcare informatics and clinical laboratory tools.