Dextran is a complex sugar (polysaccharide) made up of glucose molecules chained together, produced naturally by bacteria that feed on sucrose. It has a wide range of uses in medicine, laboratory science, and the food industry. In hospitals, it serves primarily as an intravenous fluid that expands blood volume during emergencies. In labs, it works as a calibration standard. In food production, it functions as a thickener and stabilizer.
Chemical Structure
At its core, dextran is a long chain of glucose units linked together in a specific pattern. The main backbone connects glucose molecules through what chemists call 1,6 linkages, meaning each glucose attaches to the next at a particular point on the ring-shaped molecule. Short branches sprout off this main chain at frequent intervals, connected through different attachment points (1,3 and 1,4 linkages). This branching pattern distinguishes dextran from simpler glucose chains like starch or cellulose.
Dextran comes in different sizes, measured by molecular weight in units called Daltons. The number after “dextran” refers to its average molecular weight in thousands: Dextran 40 averages around 40,000 Daltons, while Dextran 70 averages around 70,000. These size differences matter because they change how the substance behaves in the body and how long it stays in the bloodstream.
How Dextran Is Made
Commercial dextran is produced through bacterial fermentation. Several types of bacteria can make it, including species from the genera Leuconostoc, Lactobacillus, Streptococcus, and Weissella. The workhorse of commercial production is a specific strain called Leuconostoc mesenteroides NRRL B-512F, which produces the highest yields.
The process works like this: bacteria are grown in a sucrose-rich medium, and they release an enzyme called dextransucrase into the surrounding liquid. This enzyme splits sucrose apart and reassembles the glucose portions into long dextran chains. The production depends on several factors, including sucrose concentration, nitrogen sources, temperature, pH, and fermentation time. Under optimized conditions (around 25°C with 10% sucrose), bacteria can produce roughly 24 grams of dextran per liter of broth in just 16 hours. Higher sucrose and nitrogen concentrations generally push yields even further. Once fermentation is complete, the dextran is separated from the broth and purified using alcohol precipitation.
Medical Uses
Dextran’s most important medical role is as a plasma volume expander. When dissolved in saline and given intravenously, it works as a colloid, meaning it draws water into the bloodstream through osmotic pressure. This makes it useful for treating dangerously low blood volume caused by trauma, burns, or surgery, particularly when blood typing isn’t possible in time for a transfusion. For substantial blood loss, 500 to 1,000 mL of a 10% dextran solution can be infused rapidly.
The two main clinical formulations serve slightly different purposes. Dextran 70, the larger molecule, is approved for emergency volume expansion but has fallen out of favor due to its side effect profile. Dextran 40, the smaller molecule, finds use in microsurgical and vascular procedures like reconstructive plastic surgery, free flap transfers, and corneal grafts. Its particular value in these settings comes from its ability to improve blood flow through tiny vessels and reduce the tendency of platelets to clump together.
How It Works in the Body
Dextran’s effects on blood flow involve several overlapping mechanisms. It dilutes the blood, which reduces viscosity and makes it flow more easily through small vessels. It weakens the adhesive forces between blood cells and the walls of blood vessels. It also makes red blood cells more flexible, helping them squeeze through narrow capillaries. By diluting clotting factors like fibrinogen, it produces a mild anticoagulant effect. All of these properties combine to improve microcirculation, which is why surgeons value it during delicate procedures where blood flow through tiny vessels is critical.
Risks and Side Effects
Dextran carries real risks that have limited its clinical use over time. The most concerning is severe allergic reactions. A prospective study of 5,745 surgical patients who received Dextran 70 found that about 1 in 383 patients experienced some type of allergic reaction, and 1 in 821 had a severe reaction (classified as Grade III or IV). One case resulted in cardiac arrest and a neonatal death in a patient about to undergo cesarean section. In that study, the risks of dextran treatment actually exceeded the risks of the blood clots it was being used to prevent.
Kidney damage is another significant concern, especially with Dextran 40. While dextran normally increases urine output, at least 50 cases of acute kidney failure following Dextran 40 infusion have been documented. The problem occurs when blood pressure to the kidneys drops while dextran concentration is high. The dextran can become too concentrated inside the kidney’s tiny tubes, essentially solidifying and plugging them. This risk is greatest in patients who are already dehydrated or have low blood pressure. These safety issues, along with problems dextran causes with blood crossmatching tests, are why newer alternatives have largely replaced it in many hospital settings.
Laboratory Applications
Outside of medicine, dextran is a staple in research laboratories. Its most widespread scientific use is as a calibration standard in a technique called liquid chromatography, which separates and identifies complex sugar molecules. Researchers use a “dextran ladder,” a mixture of dextran fragments of known sizes, to create a reference scale. By comparing how quickly unknown sugar molecules travel through the chromatography system relative to these dextran fragments, scientists can identify and characterize glycans (sugar structures) found on proteins and cells. Dextran works well for this purpose because it is thoroughly characterized, widely available, and behaves predictably. It also serves as a calibration standard in ion mobility-mass spectrometry, another analytical technique used to study the shapes and sizes of biological molecules.
Uses in Food Production
Dextran has a growing role in the food industry. It functions as a thickener for jams and ice creams, where it prevents sugar from crystallizing, improves moisture retention, and helps maintain flavor. Because it is tasteless, food-grade, non-toxic, and highly compatible with biological systems, it fits naturally into food applications.
Recent research has explored dextran as a base material for edible food coatings. Films made from dextran combined with polyglycerol show very low water vapor permeability, meaning they effectively prevent fruits from drying out during storage. Testing on blueberries showed these coatings reduced weight loss and delayed changes in acidity and sugar content compared to uncoated fruit, meaningfully extending shelf life. This positions dextran as a promising material for developing new, biodegradable food packaging.