IgG Blood Test: Total Immunoglobulin G Explained

IgG is one of the main immunoglobulin classes. The body makes many different IgG antibodies in response to different targets. A total serum measurement adds this class together as a concentration in blood; it is not an inventory of every past infection or vaccine response.^{See reference 1,See reference 2}

IgG is often reported alongside IgA and IgM in a quantitative immunoglobulin panel. Clinicians may order the panel when investigating repeated infections, immune deficiency or an abnormal blood-protein pattern. The reason for ordering and the pattern across tests matter.^{See reference 1,See reference 2}

IgG reference intervals vary by age. Mayo Clinic Laboratories publishes separate ranges from infancy through adulthood for its serum immunoglobulin panel. Use the interval supplied with your own result; an adult range can mislead when applied to a child.^{See reference 2}

Some reports use mg/dL and others g/L. The exact unit conversion is 1 mg/dL = 0.01 g/L, so 900 mg/dL equals 9 g/L. This arithmetic does not make two laboratories’ methods identical. Convert the reference interval as well if you compare units; retain the date and laboratory for any trend.

A made-up value of 900 mg/dL is only a unit example here. It is not an “optimal” IgG target or a personal interpretation. A report flag, if present, belongs to the interval and method used for that sample.^{See reference 2}

A low IgG concentration can occur when the body makes too little immunoglobulin or loses protein. Causes can include inherited or acquired immune problems, medicines and some other conditions. One measurement does not identify the cause or show how often a person will become ill.^{See reference 1,See reference 2}

If repeated infections or another concern prompted the test, a clinician may review previous results, the other immunoglobulin classes, medicines and additional immune tests. Do not change treatment or start a supplement based on a single online range.^{See reference 1,See reference 2}

IgG may rise with a broad immune response, including chronic infection or inflammatory conditions. A concentrated rise from one antibody-producing cell population is a different possibility. Total IgG alone cannot tell these patterns apart; a clinician may use protein electrophoresis and other tests when needed.^{See reference 1,See reference 2}

A high IgG result is not proof that immunity is stronger and is not a named diagnosis. The amount measured and the ability of antibodies to respond are different questions.^{See reference 1,See reference 2}