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Test Code SFIGS IgG, Serum


Specimen Required


Only orderable as part of a profile. For more information see SFIG / Cerebrospinal Fluid (CSF) IgG Index Profile, Serum and Spinal Fluid.

 

Collection Container/Tube:

Preferred: Serum gel

Acceptable: Red top

Submission Container/Tube: Plastic vial

Specimen Volume: 1 mL

Collection Instructions: Centrifuge and aliquot serum into a plastic vial within 2 hours of collection.


Secondary ID

610784

Useful For

Aiding in the diagnosis of multiple sclerosis and other CNS inflammatory conditions

Method Name

Only orderable as part of a profile. For more information see SFIG / Cerebrospinal Fluid (CSF) IgG Index Profile, Serum and Spinal Fluid.

 

Nephelometry

Reporting Name

IgG, S

Specimen Type

Serum

Specimen Minimum Volume

0.5 mL

Specimen Stability Information

Specimen Type Temperature Time Special Container
Serum Refrigerated (preferred) 28 days
  Frozen  28 days
  Ambient  14 days

Reject Due To

Gross hemolysis OK
Gross lipemia Reject
Gross icterus OK

Clinical Information

Elevation of IgG in the cerebrospinal fluid (CSF) of patients with inflammatory diseases of the central nervous system (CNS) such as multiple sclerosis (MS), neurosyphilis, acute inflammatory polyradiculoneuropathy, subacute sclerosing panencephalitis may be due to local (intrathecal) synthesis of IgG. Elevations of CSF IgG or the CSF/serum IgG ratio may also occur as a result of permeability of the blood brain barrier, and hence, a correction using albumin measurements in CSF and serum is appropriate.

 

The CSF index is the CSF IgG to CSF albumin ratio compared to the serum IgG to serum albumin ratio. The CSF index is, therefore, an indicator of the relative amount of CSF IgG compared to serum. Any increase in the index is a reflection of IgG production in the CNS. The IgG synthesis rate is a mathematical manipulation of the CSF index data and can also be used as a marker for CNS inflammatory diseases. The test is commonly ordered with oligoclonal banding or immunoglobulin kappa free light chains in CSF to aid in the diagnosis of demyelinating conditions.

Reference Values

Only orderable as part of a profile. For more information see SFIG / Cerebrospinal Fluid (CSF) IgG Index Profile, Serum and Spinal Fluid.

 

0-4 months: 100-334 mg/dL

5-8 months: 164-588 mg/dL

9-14 months: 246-904 mg/dL

15-23 months: 313-1,170 mg/dL

2-3 years: 295-1,156 mg/dL

4-6 years: 386-1,470 mg/dL

7-9 years: 462-1,682 mg/dL

10-12 years: 503-1,719 mg/dL

13-15 years: 509-1,580 mg/dL

16-17 years: 487-1,327 mg/dL

≥18 years: 767-1,590 mg/dL

Interpretation

Cerebrospinal fluid (CSF) IgG synthesis rate indicates the rate of increase in the daily CSF production of IgG in milligrams per day. A result greater than 12 mg/24h is elevated.

 

A CSF index greater than 0.85 is elevated and indicative of increased synthesis of IgG.

Method Description

The test is performed by nephelometry. The light scattered onto the antigen-antibody complexes is measured. The intensity of the measured scattered light is proportional to the amount of antigen-antibody complexes in the sample under certain conditions. If the antibody volume is kept constant, the signal behaves proportionally to the antigen volume.

 

A reference curve is generated by a standard with a known antigen content on which the scattered light signals of the samples can be evaluated and calculated as an antigen concentration. Antigen-antibody complexes are formed when a sample containing antigen and the corresponding antiserum are put into a cuvette. A light beam is generated with a light emitting diode (LED), which is transmitted through the cuvette. The light is scattered onto the immuno-complexes that are present. Antigen and antibody are mixed in the initial measurement, but no complex is formed yet. An antigen-antibody complex is formed in the final measurement.

 

The result is calculated by subtracting value of the final measurement from the initial measurement. The distribution of intensity of the scattered light depends on the ratio of the particle size of the antigen-antibody complexes to the radiated wavelength.(Instruction manual: Siemens Nephelometer II Operations. Siemens, Inc; V 2.3, 2008; Addendum to the Instruction Manual 2.3, 08/2017)

Day(s) Performed

Monday through Friday

Performing Laboratory

Mayo Clinic Laboratories in Rochester

Test Classification

This test has been cleared, approved, or is exempt by the US Food and Drug Administration and is used per manufacturer's instructions. Performance characteristics were verified by Mayo Clinic in a manner consistent with CLIA requirements.

CPT Code Information

82784

LOINC Code Information

Test ID Test Order Name Order LOINC Value
SFIGS IgG, S 2465-3

 

Result ID Test Result Name Result LOINC Value
IGG_S IgG, S 2465-3
AIGAS IgG/Albumin, S 6782-7