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Alpha-1 Globulin, SPEP (percent)

The share of your serum protein in the alpha-1 zone on electrophoresis, mostly alpha-1 antitrypsin. Reported as a percent of total protein.

AI-verified against cited sources. Awaiting expert reviewLOINC 13978-2

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What it is

Protein electrophoresis uses an electric current to sort the proteins in your blood serum into groups. The alpha-1 group is a thin band that sits next to albumin. Most of it is alpha-1 antitrypsin (AAT), a protein that helps protect the lungs from damage by enzymes. The band also holds thyroid-binding globulin and transcortin, which carry hormones in the blood.

Why it matters

Several proteins in this band rise with inflammation and in pregnancy, so it works as a rough signal of inflammation. A very small or missing band is uncommon and can be a clue to alpha-1 antitrypsin deficiency, which is checked with a direct AAT blood test. Many results outside the range have simple explanations, such as a recent infection. Your clinician reads this together with the rest of the pattern.

If it’s low

A low alpha-1 band is uncommon. It can be a sign of alpha-1 antitrypsin (AAT) deficiency, an inherited condition that can affect the lungs and liver. It can also go with a liver that is making less protein. A direct AAT blood test, not electrophoresis, is used to look at this more closely. Many other things can cause this, and your clinician can put it in context.

Common causes

  • A result just under the lower limit, which happens in a small share of healthy people because ranges are set that way
  • Alpha-1 antitrypsin deficiency (inherited)
  • Liver disease that lowers protein production

What can help

  • Ask whether a direct alpha-1 antitrypsin blood test is worth doing
  • Tell your clinician about any family history of lung or liver disease

If it’s high

A higher alpha-1 band means more of the proteins that rise with inflammation are in your blood. Short-term infections and other causes of inflammation are common reasons, and pregnancy also raises it. Long-lasting inflammatory conditions and some cancers are less common reasons. Many other things can cause this, and your clinician can put it in context.

Common causes

  • Recent infection or other short-term inflammation
  • Pregnancy
  • Oral contraceptives (reported to raise AAT, the main protein in this band)
  • Long-lasting inflammatory conditions such as rheumatoid arthritis
  • Some cancers

What can help

  • Ask whether a recent illness could explain it, and whether a repeat test after you recover makes sense
  • Ask whether an inflammation test such as CRP would add useful information

Usual ranges

What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.

For adults: 2.9–4.9 %. Source: International Journal of General Medicine, Diagnostics (Basel).

What can affect your result

  • Inflammation, infection and pregnancy raise this band
  • Oral contraceptives are reported to raise AAT, the main protein in the band
  • Liver disease can lower it
  • Changes in the other fractions: the share is relative, so a big rise in another fraction can push it down
  • Method and sex: capillary and gel systems differ, and one study of healthy adults found slightly different alpha-1 percentages in men and women
  • The result is a share of the total, so a change in another fraction (for example a rise in antibodies) moves it even when the amount of this protein has not changed.
  • A blood sample in which red cells broke open (hemolysis) can distort the alpha and beta zones and create false patterns.
  • Plasma instead of serum adds fibrinogen, which can show up as an extra band. ARUP does not accept plasma for this test.
  • Iodinated contrast dye and some antibiotics can cause artifacts on the tracing.
  • Certain medicines can affect protein results (MedlinePlus). Check with your clinician before changing any medicine.
  • Some sources say you may be asked not to eat or drink for up to 12 hours before the draw (MedlinePlus), while others say no preparation is needed (Cleveland Clinic). Follow the instructions from your lab.

Depends on the cause. This band follows inflammation, so it tends to move as an illness comes and goes.

When to talk to a clinician

Talk with your clinician if your lab flagged this result, or if the report mentions a very small or missing alpha-1 band. Let them know sooner about shortness of breath that does not go away, a long-lasting cough or wheeze, or yellow skin or eyes.

Questions you could ask

  • How does the alpha-1 result fit with my other protein fractions?
  • Could a recent illness, pregnancy or a medicine explain a higher alpha-1 band?
  • Should we repeat it after I recover?
  • Would a direct alpha-1 antitrypsin level be useful?
  • Does my family history of lung or liver disease change what we check?

Questions people ask

Does a low alpha-1 percent mean I have alpha-1 antitrypsin deficiency?

Not necessarily. A small alpha-1 band is one clue, and a direct blood test for AAT is needed to check. In a Spanish hospital study of 12,800 electrophoresis tests, 40 had an alpha-1 share below 3%, and 14 of them had a low AAT level when it was measured directly.

How can I turn this percent into g/dL?

Multiply the percent by your total protein and divide by 100. For example, a 4% alpha-1 share with a total protein of 7.0 g/dL is 0.28 g/dL.

Why does my lab's range differ from the one shown here?

Labs use different instruments and set ranges from different groups of healthy people. Published ranges for the alpha-1 share run from about 2% to 10%. Use the range printed on your own report first.

Show the science and sources

For clinicians and researchers

The alpha-1 zone lies between albumin and alpha-2. AAT is the most abundant protein in it, with thyroxine-binding globulin and transcortin also in the band (AFP 2005). Software reports the zone as a percent of the total area under the tracing, so a large M-spike or a polyclonal rise in gamma globulin can push the alpha-1 percent down without any fall in the amount of alpha-1 protein; percent x total protein / 100 gives the g/dL value. AAT is an acute-phase reactant, so the band rises with inflammation and pregnancy (AFP 2005), and higher AAT values are also described with pregnancy and oral contraceptive use (Fernandez-Gomez 2023). People with one deficient gene copy whose AAT sits near the lower limit of normal can be missed by measurement alone (Fernandez-Gomez 2023). In that Spanish capillary electrophoresis study, an alpha-1 share below 3% was seen in 40 of 12,800 tests, 14 of those had AAT below 100 mg/dL, and 10 of the 11 people who took part had a SERPINA1 variant. The 3% cut-off was a local screening threshold, not a reference limit. Confirmation of AAT deficiency uses a direct AAT level plus phenotype or genotype testing. Intervals are method specific: Sebia Capillarys 2.9-4.9%, the Spanish paper quotes 3-4%, and a 297-adult Addis Ababa study found 3.0-5.4% (men) and 3.4-5.6% (women). Hemolysis and fibrinogen interference (fibrinogen is present in plasma, not serum) can create artifacts in the alpha and beta zones (J Clin Med 2025), and ARUP does not accept plasma.

LOINC 13978-2 (primary). Specimen: serum.

Sources

  1. Establishment of Reference Intervals for Serum Protein Electrophoresis of Apparently Healthy Adults in Addis Ababa, Ethiopia, International Journal of General Medicine (2022)
  2. Utility of the Serum Protein Electrophoresis in the Opportunistic Screening for the Deficiency of Alpha-1 Antitrypsin, Diagnostics (Basel) (2023)
  3. Understanding and Interpreting Serum Protein Electrophoresis, American Family Physician (2005)
  4. Protein electrophoresis - serum, MedlinePlus (National Library of Medicine) (2026)
  5. Multiple Myeloma Laboratory Diagnostics Made Simple: Practical Insights and Key Recommendations, Journal of Clinical Medicine (2025)
  6. Evaluation of an automated capillary electrophoresis system for serum protein electrophoresis with the determination of gender-specific reference values, Clinical Laboratory (2010)
  7. Feasibility evaluation of big data algorithms for establishing serum protein electrophoresis reference intervals using Hoffmann and refineR methods, Clinica Chimica Acta (2025)
  8. Protein Electrophoresis, Serum (test 0050640), ARUP Laboratories
  9. Serum Protein Electrophoresis (SPEP) Test, Cleveland Clinic
  10. LOINC code lookup (NLM Clinical Tables), National Library of Medicine

AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.

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