Globulins IgG

If you keep catching sinus infections, bronchitis, or pneumonia that never quite explains itself, this is one of the first numbers worth checking. It measures the main antibodies your body uses to fight infection, and when they run low, years of repeated illness often get blamed on bad luck instead.

The same number cuts the other way too. When it runs high, it can signal that your immune system is chronically switched on, a pattern that shows up in conditions ranging from liver disease to severe infection.

What This Number Reflects

IgG (immunoglobulin G) is the most common antibody in your blood, making up about 75% of all the antibodies circulating in your body. It is produced by immune cells called B cells and plasma cells after they meet a germ or a vaccine. Your level is the single most reliable everyday snapshot of whether this antibody-making system is working.

One caveat matters up front. A normal total level does not guarantee your antibodies actually work, because you can carry plenty of IgG that fails to target specific germs. That is why doctors sometimes pair the number with tests of how well you respond to vaccines.

When Your Level Runs Low

A low level means your body is not making enough antibodies, a state called hypogammaglobulinemia. The most important consequence is infection: recurrent chest, sinus, and gut infections are the classic sign. The catch is that this is easy to miss on a standard checkup.

In one Australian group of adults with antibody deficiency, symptoms typically started around age 20 but a diagnosis was not made until around age 35. Diagnostic delays have shortened in recent decades, with 5 to 8 years now common across many countries, though historically gaps of 15 years or more were reported. Any delay matters, because untreated deficiency can lead to permanent lung scarring (called bronchiectasis) and other lasting damage.

Even modestly low levels carry risk. In a study of about 1,500 people with or at risk for COPD (a chronic lung disease), those in the lowest third for IgG had roughly 28% more flare-ups than the rest. Low levels of two IgG building blocks, IgG1 and IgG2, were tied to about 39% and 50% higher rates of severe flares.

The most severe form of deficiency is common variable immunodeficiency (CVID), the most frequent serious antibody disorder. Beyond recurrent infection, it carries higher rates of autoimmune disease and sometimes liver and lymph-node complications.

When Your Level Runs High

A high level usually means your immune system has been stimulated over a long stretch, whether by chronic infection, autoimmune disease, or ongoing inflammation. In several conditions, a high value tracks worse outcomes rather than better protection.

In a study of 261 people with a fatty liver condition called non-alcoholic steatohepatitis, those with elevated IgG were about 7 times as likely to progress to liver failure and nearly 4 times as likely to die over follow-up.

The pattern shows up elsewhere too. In one large sepsis trial, higher IgG on the first day of illness was linked to roughly 80% higher 28-day mortality, though a later meta-analysis found no overall difference in IgG between sepsis survivors and non-survivors, so this link is not settled. In cystic fibrosis, an elevated level was tied to a much greater risk of progressing to severe lung disease.

Why Both High and Low Can Be Bad

This is not a simple higher-is-better or lower-is-better number. Think of it as a status light for your immune system rather than a score. A low level signals a weak defense that lets infections slip through. A high level usually signals a defense stuck in overdrive, pointing to underlying inflammation or disease driving it up. Same molecule, opposite problems, and the meaning depends entirely on the clinical picture around it.

A Hint Hidden in Routine Bloodwork

There is a shortcut buried in a standard metabolic panel. A value called calculated globulin, worked out from total protein minus albumin, tracks with IgG. In a study of children, the two correlated strongly (0.83, where 1.0 would be a perfect match); in adults the link is somewhat looser but still useful. A low calculated globulin is a red flag that your IgG may be low, and this shortcut has caught cases of antibody deficiency that were later confirmed and treated.

Why One Reading Is Not Enough

A single reading is a snapshot, and the number shifts with age, infection, and medication. What tells the real story is the trajectory. If you are starting a treatment that suppresses antibodies, a baseline now plus follow-up readings can show your defenses being eroded before an infection reveals it.

Get a baseline, then retest in 3 to 6 months if you are on immune-suppressing treatment or making changes, and at least once a year otherwise. If you are on antibody replacement therapy, tracking the number is how you confirm it is holding your level where it protects you.

What to Do With an Out-of-Pattern Result

A single abnormal reading is a starting point, not a diagnosis. If your level is low, the next step is to measure the other main antibodies, IgA and IgM, and often the IgG subclasses, to see whether the whole antibody system is affected or only part of it.

Combinations matter more than any one value. A low level plus a history of recurrent infection or an affected family member points toward antibody deficiency and is worth a referral to an immunologist, who can test how you respond to vaccines. A high level with no obvious infection is worth investigating for autoimmune or inflammatory disease, sometimes with protein electrophoresis (a test that separates blood proteins) to check for abnormal antibody-producing cells.

When Results Can Be Misleading

Several things can distort a single reading and send you toward the wrong conclusion. The biggest one is timing around illness, so a value drawn while you are sick may not reflect your true baseline.

• Recent infection or vaccination: can push the number up temporarily, so a value drawn soon after illness may overstate your usual level.
• Ancestry and sex: average levels differ across groups. Black and Asian patients had higher average IgG than White patients in a large study, so a fixed reference range can misclassify people near the edges.
• Protein loss: conditions that leak protein through the gut or kidneys can lower the number even when antibody production is normal.
• Strong inflammation: this can raise total globulin enough to hide a true deficiency on the calculated-globulin shortcut, producing a falsely reassuring screen.