Proteins are the building blocks of life, and among them, albumins play a crucial role in maintaining our body’s balance and health. From regulating blood pressure to transporting vital substances, albumin is indispensable. In fact, measuring serum albumin levels is one of the most common diagnostic tests in hospitals worldwide.
In this article, we will explore albumins in depth — their structure, functions, sources, clinical significance, and related disorders — in a simple and exam-friendly manner.
Definition and overview
What are albumins?
Albumins are a family of water‑soluble, non-glycosylated globular proteins. The most common member is serum albumin, the chief protein of blood plasma, accounting for about 50–60% of plasma proteins and crucial for maintaining colloid (oncotic) pressure and transporting diverse ligands.
Where are they found?
Commonly in blood plasma; other proteins also called “albumins” occur in egg white (ovalbumin), milk (lactalbumin), and some plant seeds (2S albumins) due to their egg‑white–like coagulation behavior.
Synthesis and site
Serum albumin is synthesized exclusively by liver hepatocytes and released into blood; it is a standard marker in liver/kidney function panels and nutrition assessment.
◾Explore This Topic: Composition of Serum: Components, Functions & Clinical Importance
Structure and general properties
Molecular details
Human serum albumin (HSA) is ~65–70 kDa, a single chain of ~585 amino acids arranged in three homologous domains (I–III) with subdomains (A, B), forming a heart‑shaped protein; its isoelectric point is ~4.7.
It is water‑soluble, heat‑denaturable, and structurally stabilized by multiple intrachain disulfide bonds.
Plasma kinetics
Normal plasma concentration is roughly 3.5–5.5 g/dL; albumin’s plasma half-life is ~20 days (lab-specific ranges vary).
Types of albumins
Serum albumins (vertebrates; the “albumin family”)
- Human serum albumin (HSA) — main plasma protein and transport carrier.
- Alpha‑fetoprotein (AFP) — fetal plasma protein.
- Vitamin D–binding protein and afamin — transport specialized ligands.
These albumin-family proteins are evolutionarily related and found only in vertebrates.
Food/other “albumins” (not in the same family but called albumins)
- Ovalbumin — storage protein in egg white (a serpin).
- Lactalbumin (whey fraction) — milk protein fraction; milk also contains some serum albumin.
- Plant 2S albumins — small seed storage proteins named for coagulation behavior.
Applied/Industrial classifications
- In medicine/biotech you’ll often see: HSA (human), BSA (bovine), and recombinant albumin used in labs and therapeutics.
Functions of albumins
In the human body
- Maintains oncotic pressure and fluid balance
Albumin is the dominant contributor to plasma oncotic pressure, keeping fluid within the vasculature and countering edema and third spacing (ascites).
- Transporter (“molecular taxi”)
Binds and carries water, cations, fatty acids, bilirubin, thyroid hormone (T4), steroid hormones, vitamins, and many drugs—affecting pharmacokinetics and free drug levels.
- Antioxidant and toxin binding
Scavenges reactive species and binds toxins/waste, aiding cellular protection and detox handling.
- Buffer and pH support; amino acid reservoir
Contributes to acid‑base buffering and serves as a limited amino acid source during stress or malnutrition.
These roles make serum albumin central to hemodynamics, drug transport, and overall metabolic homeostasis.
In plants (if asked)
- 2S albumins
Small seed storage proteins (e.g., in hemp), named for albumin-like coagulation features; they are structurally distinct from vertebrate serum albumins.
Clinical significance
- Hypoalbuminemia (low albumin)
Causes include chronic liver disease (reduced synthesis), nephrotic syndrome/CKD (urinary loss), malnutrition/malabsorption, inflammation/infection, severe burns/trauma, and protein-losing states. Clinical effects include edema and ascites due to reduced oncotic pressure.
- Hyperalbuminemia (high albumin)
Uncommon; most often reflects dehydration or severe diarrhea; occasionally high-protein intake or certain drugs can elevate measured levels.
- Why clinicians care
Serum albumin is part of CMP/LFT panels, helps assess liver/kidney function and nutrition, and correlates with outcomes across conditions; urinary albumin (microalbumin) detects early diabetic kidney disease.
- Therapeutic use
IV albumin may be used in select settings (e.g., cirrhosis-related complications, burns/trauma, septic shock) for volume expansion and colloid support as per clinical judgment and protocols.
Sources: Natural dietary protein to support albumin synthesis
- Animal: Eggs, milk/curd/yogurt, paneer, fish, chicken, lean meats.
- Plant: Pulses/legumes (dal, chana, rajma, soy/ tofu), nuts, seeds, whole grains.
- Tip for aspirants: Think “complete protein” (egg, dairy, soy) + “pulse–cereal” combinations (e.g., dal–rice, khichdi) for better amino acid balance.
Your body synthesizes albumin in the liver using dietary amino acids (so “sources of albumin” in diet = “sources of protein”). No citation required.
Tests and measurements
- Albumin blood test (serum albumin)
Part of CMP/LFT; typical adult reference range ≈ 3.5–5.5 g/dL (labs vary). Low suggests liver/kidney disease, malnutrition/inflammation; high often dehydration. Follow-up may include total protein, A/G ratio, and electrophoresis.
- Urine albumin (microalbumin) or albumin/creatinine ratio (UACR)
Early marker of diabetic/hypertensive kidney damage; a key screening tool in primary care and endocrinology/nephrology.
- Albumin-to-globulin (A/G) ratio
Helpful adjunct for chronic infections, autoimmune disorders, and liver/kidney disease workups.
- Where these tests sit
Included in comprehensive metabolic panels and liver panels; methods include dye-binding, immunochemical methods, and urine dipstick/quantitative assays.
Exam‑oriented facts (high-yield)
- Serum albumin = ~50–60% of plasma proteins; site of synthesis: liver.
- Molecular mass ≈ 66.5–70 kDa; single chain, three domains; ~585 amino acids.
- Isoelectric point (pI) ≈ 4.7; non-glycosylated; water‑soluble; heat‑denaturable.
- Normal serum range ≈ 3.5–5.5 g/dL (lab-specific); plasma half‑life ≈ 20 days.
- Key functions: oncotic pressure, transport of ligands/drugs, antioxidant, buffer.
- Urine microalbumin = early diabetic nephropathy screen; A/G ratio aids differential.
- Hyperalbuminemia = dehydration; hypoalbuminemia = liver disease, nephrotic loss, malnutrition/inflammation.
Quick revision table
| Topic | Key points for exams |
|---|---|
| Definition | Major plasma protein maintaining oncotic pressure and transporting ligands; non‑glycosylated globular protein |
| Structure | ~66.5–70 kDa; single chain (~585 aa), 3 domains (I–III), subdomains A/B; pI ~4.7 |
| Types | Serum albumin (HSA/BSA/recombinant), ovalbumin (egg), lactalbumin (milk whey), AFP, vitamin D–binding protein, plant 2S albumins |
| Functions | Oncotic pressure, transport (fatty acids, bilirubin, hormones, drugs), antioxidant, buffering, amino acid reservoir |
| Normal range | Serum ~3.5–5.5 g/dL (lab-dependent); half‑life ~20 days |
| Tests | Serum albumin (CMP/LFT), urine microalbumin/UACR, A/G ratio, protein electrophoresis |
| Low albumin | Liver disease, nephrotic loss/CKD, malnutrition/malabsorption, inflammation, burns/trauma |
| High albumin | Dehydration (most common) |
| Therapy | IV albumin in select scenarios: cirrhosis complications, burns/trauma, sepsis (protocol-based) |
Note: Ranges and structural points are aligned to standard references and clinical sources commonly used in exams.
Real-life connections and analogies
- Oncotic pressure: Albumin is the body’s “sponge,” holding water inside vessels—like a dam that prevents water from leaking into fields (tissues).
- Transport: A “fleet of taxis,” ferrying hormones, fatty acids, bilirubin, and medicines to destinations.
- Antioxidant: A “rust guard,” binding reactive molecules before they damage tissues.
- Buffer: A “shock absorber” for pH changes—small adjustments, big stability.
Exam trends and likely question formats
- MCQs
- Site of albumin synthesis (liver); % of plasma protein; function in oncotic pressure; normal range; pI value; causes of hypo-/hyperalbuminemia; which test detects early diabetic nephropathy (urine microalbumin).
- Match the following
- Protein ↔ source (ovalbumin—egg; lactalbumin—milk); Test ↔ purpose (A/G ratio—chronic infection/autoimmune/liver/kidney evaluation).
- One-liners
- “Main function of serum albumin,” “Half‑life,” “Non‑glycosylated plasma protein,” “pI of albumin.”
Tip: Many PYQs revolve around “function + test + range.” Practice with timer to cement recall.
FAQs
What are albumins?
Albumins are water‑soluble globular proteins; serum albumin is the principal plasma protein that maintains oncotic pressure and transports various ligands.
What is serum albumin?
The main protein of human plasma (~50–60% of plasma proteins), synthesized in the liver; it regulates oncotic pressure and transports fatty acids, bilirubin, hormones, and drugs.
What causes low albumin levels?
Common causes: chronic liver disease (low synthesis), nephrotic syndrome/CKD (urinary loss), malnutrition/malabsorption, inflammation, burns/trauma; clinically leads to edema/ascites.
What is the albumin test?
A blood test (part of CMP/LFT) measuring serum albumin (~3.5–5.5 g/dL). Low suggests liver/kidney disease or malnutrition; high usually dehydration. Urine microalbumin screens early kidney damage.
How can I naturally support healthy albumin levels?
Ensure adequate protein intake (eggs, dairy, legumes, lean meats/soy), manage chronic liver/kidney conditions with medical guidance, and address inflammation/infection promptly. The liver uses dietary amino acids to synthesize albumin. No citation required.
