In medicine and biology, “bodies” is a term used to describe distinct structures found inside cells, in the blood, or in tissue samples. These aren’t full organisms. They’re tiny clusters of protein, DNA fragments, fat byproducts, or other material that doctors can identify under a microscope or through lab tests. Finding certain types of bodies in your blood work or a biopsy often points to a specific condition, from liver disease to a missing spleen to a viral infection. Here’s what the most common types mean and why they matter.
Ketone Bodies: Your Backup Fuel Source
Ketone bodies are molecules your liver produces when your body runs low on carbohydrates and starts burning fat for energy instead. There are three types: acetoacetate, beta-hydroxybutyrate, and acetone. Unlike large fat molecules, ketone bodies can cross into the brain, making them the brain’s primary backup fuel during fasting or very low-carb diets. Your heart and skeletal muscles also use them.
Having some ketone bodies in your blood is normal and can happen after skipping a meal or during intense exercise. A blood ketone level below 0.6 mmol/L is considered normal. Levels between 0.6 and 1.5 mmol/L signal low to moderate risk and warrant a call to your doctor, especially if you have diabetes. Once levels climb above 1.6 mmol/L, the risk of diabetic ketoacidosis rises sharply, and anything above 3.0 mmol/L is a medical emergency requiring immediate care. For people without diabetes who are intentionally following a ketogenic diet, mild ketone elevation is expected and generally not dangerous.
Howell-Jolly Bodies: A Clue About Your Spleen
Howell-Jolly bodies are tiny remnants of DNA left inside red blood cells. Normally, your spleen filters these out as blood cells mature and circulate. When Howell-Jolly bodies show up on a routine blood smear, it almost always means your spleen isn’t working properly or has been removed.
They’re considered a hallmark sign of splenic dysfunction. You might see them after a splenectomy (surgical removal of the spleen), in people born without a spleen, or in conditions like sickle cell disease where the spleen gradually loses function. They also appear in megaloblastic anemia, where red blood cell production itself is abnormal. Howell-Jolly bodies don’t cause symptoms on their own. They’re a diagnostic flag that tells your doctor to investigate spleen health and, if the spleen isn’t functioning, to take precautions against certain infections the spleen normally helps fight.
Heinz Bodies: Damaged Hemoglobin
Heinz bodies are clumps of damaged hemoglobin, the protein inside red blood cells that carries oxygen. They form when hemoglobin becomes chemically unstable and denatures, sticking together in small clusters visible under a microscope with special staining. The most well-known cause is G6PD deficiency, an inherited enzyme shortage that makes red blood cells vulnerable to oxidative stress from certain foods (like fava beans), medications, or infections. Other hemolytic anemias can produce them as well.
When Heinz bodies accumulate, the affected red blood cells become rigid and get destroyed faster than normal, leading to anemia. If your lab results mention Heinz bodies, your doctor will typically investigate for an underlying cause of red blood cell damage.
Lewy Bodies: Protein Clumps in the Brain
Lewy bodies are abnormal deposits of a protein called alpha-synuclein that build up inside nerve cells in the brain. They’re the defining feature of two major conditions: Parkinson’s disease and Lewy body dementia. In some cases, other proteins like amyloid-beta and tau (also linked to Alzheimer’s) accumulate alongside alpha-synuclein, which may explain why symptoms of these diseases sometimes overlap.
Lewy body dementia has a distinct pattern. The core symptoms include fluctuating alertness and attention (good days and bad days that shift noticeably), vivid and detailed visual hallucinations, sleep behavior disorder where a person physically acts out dreams, and movement symptoms similar to Parkinson’s like stiffness, slow movement, or tremor. A probable diagnosis requires at least two of these core features. Memory problems may not appear early on, which sometimes leads to misdiagnosis. People with Lewy body dementia also tend to be unusually sensitive to antipsychotic medications, which can cause severe reactions.
Inclusion Bodies: Signs of Viral Infection
Inclusion bodies are structures that form inside cells during certain viral infections. They were first described in rabies, where they’re called Negri bodies, and similar formations appear in cells infected by other viruses. Under a microscope, they look like distinct clusters within the cell’s interior.
These structures aren’t random debris. They function as miniature viral factories, concentrating the materials a virus needs to copy itself. They pull together viral proteins and genetic material, shield them from the immune system, and coordinate the steps of viral replication in an organized way. For pathologists, finding inclusion bodies in a tissue sample serves as direct histological proof of viral infection and can help identify which virus is responsible.
Mallory-Denk Bodies: Markers of Liver Damage
Mallory-Denk bodies are clumps of damaged structural proteins found inside liver cells. First identified in 1911 in patients with alcoholic hepatitis, they were long considered a sign of alcohol-related liver damage. Doctors now know they also appear in non-alcoholic fatty liver disease, hepatitis B and C, certain cholestatic liver diseases, Wilson disease, and liver cancer.
These bodies form inside swollen, injured liver cells (called “ballooned hepatocytes”), though not every damaged liver cell contains them. They range from 3 to 24 nanometers in diameter and come in several structural subtypes that pathologists classify during biopsy evaluation. Finding Mallory-Denk bodies on a liver biopsy doesn’t pinpoint a single disease, but it does confirm that significant liver cell injury is occurring and helps guide the severity grading of whatever liver condition is present.
Polar Bodies: Byproducts of Egg Cell Division
Polar bodies are small cells produced when an egg cell divides during its maturation process. They contain a copy of the egg’s genetic material but have no role in fertilization or embryo development. Essentially, they’re cellular waste products.
In fertility medicine, polar bodies have found a practical use. Because they carry a mirror image of the egg’s DNA, doctors can biopsy them to screen for genetic abnormalities inherited from the mother, including chromosomal problems and single-gene disorders. This is done as part of preimplantation genetic testing during IVF cycles. The main limitation is that polar body biopsy only analyzes the maternal genetic contribution. A trophectoderm biopsy, which samples cells from a developing embryo, can assess both maternal and paternal genes and is more commonly used today. Still, polar body biopsy remains a useful option in some clinical situations, particularly in countries where embryo biopsy faces legal restrictions.