Fluid Proteins

Normal total serum protein is about 6.0–8.3 g/dL (60–83 g/L). Cerebrospinal fluid (CSF) protein is much lower, typically 15–45 mg/dL (0.15–0.45 g/L). Other body fluids (pleural, peritoneal) normally have low protein; higher values suggest exudative disease—for example, pleural protein >2.9 g/dL or pleural/serum protein ratio >0.5 suggests an exudate. Check lab-specific ranges.

Body fluids contain many proteins: albumin (the major plasma protein); globulins including immunoglobulins/antibodies; clotting proteins such as fibrinogen and clotting factors; complement proteins; transport proteins (transferrin, ceruloplasmin); enzymes (amylase, lipase, proteases); peptide hormones (insulin, growth factors); mucins and antimicrobial proteins (lysozyme, lactoferrin); and regulatory cytokines. Abundance varies by fluid.

Amniotic fluid contains several major proteins, notably albumin and alpha‑fetoprotein (AFP), plus immunoglobulins (primarily IgG), fibronectin, transferrin and mucins. It also contains lactoferrin, complement proteins, various enzymes (e.g., alkaline phosphatase, LDH), and growth factors/cytokines such as epidermal growth factor, TGF‑β and IL‑6, supporting fetal development and immune protection; small amounts of keratinaceous proteins from vernix are present.

A protein test commonly uses blood (serum) to measure total protein, albumin and globulin levels, or urine to detect albuminuria/proteinuria for kidney function. Cerebrospinal fluid may be tested when neurological disease is suspected. Collection methods: a blood draw, a clean‑catch urine sample, or lumbar puncture for CSF. Results help diagnose liver, kidney, immune, or inflammatory conditions.

Blood plasma is the body fluid highest in protein, rich in albumin and globulins. These plasma proteins maintain oncotic pressure, transport hormones, nutrients and drugs, and support immunity and clotting. Total plasma protein normally averages about six to eight grams per deciliter; abnormal levels may signal dehydration, liver disease, infection, or immune disorders.

Elevated total protein usually reflects increased globulins or reduced plasma volume (dehydration). Causes include chronic inflammation, infections, autoimmune disorders, and plasma-cell disorders such as multiple myeloma. Very high levels can cause hyperviscosity with headaches, vision changes, bleeding or thrombosis. Evaluation typically requires repeat testing and specialized tests (serum protein electrophoresis, immunofixation) and medical assessment to identify the underlying cause.