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LOINC Code 4691-2: Viscosity (P) [Visc]

4691-2 is a LOINC code used to identify Viscosity (P) [Visc] in laboratory and clinical observation data. You may see this code in lab systems, lab reports, EHR exports, interoperability feeds, or other structured clinical data exchanges. LOINC codes identify tests, measurements, observations, survey items, and clinical questions in a standardized way. It is associated with the component Viscosity. It is commonly used with the system or sample type Plas.

Reviewed by HealthAssure Clinical TeamUpdated 25 May 2026

What is this code?

LOINC codes identify tests, measurements, observations, survey items, and clinical questions in a standardized way. It is associated with the component Viscosity. It is commonly used with the system or sample type Plas.

When is it used?

  • Used in lab systems, EHRs, and clinical data exchange.
  • May identify a test, observation, survey item, or clinical document request rather than a diagnosis.
  • Status: ACTIVE
  • Order vs observation: Both

What it does not mean

  • The code identifies the observation or test, not the actual result.

Key facts

Viscosity of Plasma
Viscosity
Plasma and serum viscosity measurements are used in the clinical management of patients with hyperviscosity syndrome, which is caused by a variety of clinical diagnoses, such as polycythemia, Waldenström macroglobulinemia, multiple myeloma, and occasional cases of rheumatoid arthritis, SLE, systemic lupus erythematosus, hyperfibrinogenemia and leukemia. Common symptoms of hyperviscosity are, bleeding, visual signs or symptoms, and neurologic deficits. The viscosity at which symptoms develop is variable, but they rarely appear below a serum or plasma viscosity of 3 cP. Viscosity is reported in units defined as "rel to H2O", and are expressed in centipoise (cP). [PMID16830959] Whole blood viscosity is increased in polycythemia, rouleau formation, and other conditions listed for serum and plasma, but may be of limited clinical value because of the differences in shear rates between the instrument and in vivo conditions.[Tietz]
Pl; Plasma; Plsm; Point in time; QNT; Quan; Quant; Quantitative; Random; SPEC; Vicos; Viscos; Viscosity

Where you may see this code

You may see this code in lab systems, lab reports, EHR exports, interoperability feeds, or other structured clinical data exchanges.

Common synonyms

Viscosity (P) [Visc]Viscosity of PlasmaVisc PlasViscositySPECViscosity, BloodVisc

Frequently asked questions

Code details

Code4691-2
SystemLOINC
Display nameViscosity (P) [Visc]
DescriptionViscosity
Short nameVisc Plas
ComponentViscosity
PropertyVisc
TimingPt
System (specimen)Plas
ScaleQn
ClassSPEC
Example unitscP
StatusACTIVE
Order/ObservationBoth

Flags

BillableNo
Valid clinical useNo

Source

SourceLOINC
Version2.82
Releasemain
First released1.0
Last changed2.73

Consumer names

Viscosity, Blood

Part names

ViscosityViscPtPlasQnPoint in time (spot)Plasma

About this content

This page is prepared by HealthAssure's clinical team using official coding standards from LOINC. AI tools assist with drafting explanations, which are then reviewed and verified by healthcare professionals for accuracy. This content is for informational purposes and does not replace professional medical advice. Meet our team.

LOINC Code 4691-2 | HealthAssure