Burr cells are red blood cells with a spiky outline. They turn up in a short list of conditions, most notably kidney failure, dehydration, and certain salt and phosphate imbalances. Rarer causes include an inherited enzyme disorder called pyruvate kinase deficiency, severe burns, and snake or insect venom. But the same shape change can happen in a tube of blood sitting on a lab bench, so a burr cell on a report is as often a sign of how the sample was handled as of anything going on in your body.1Free Medical Textbook. ANEMIA OF CHRONIC RENAL FAILURE The finding is a clue to read alongside your other results, not a diagnosis by itself.
What a Burr Cell Looks Like on Your Report
A burr cell has 10 to 30 short, blunt bumps spaced evenly all the way around its edge, like a bottle cap.2The Blood Project. Echinocytes (Burr Cells) It keeps the pale center a normal red cell has, which shows it is still basically a flat disc.3The Blood Project. Echinocytes (Burr Cells) Reports may call it an echinocyte, a crenated cell, or a spiculated cell. All mean the same thing.4eClinpath. Quick guide Labs usually grade how many they see as few, moderate, or many.5eClinpath. Quick guide
You will not find burr cells in the standard machine counts. They are spotted on a blood smear, which is a drop of blood spread thin on a glass slide and stained. A person or software looks at that slide, and the result usually appears as a “red cell morphology” or “smear review” comment on a CBC report.
A grade of “few” means only an occasional burr cell was seen among thousands of red cells. That is the most common situation on a routine report and is often a handling effect. “Many” means a large share of the cells on the slide have the shape, which is more likely to reflect something in the sample or the body and is worth following up. Grades are a technician’s visual estimate, so one lab’s “moderate” may be another lab’s “many.” Compare reports from the same lab when you can.
The bumps form when the outer layer of the cell’s membrane expands a little relative to the inner layer.6eClinpath. Quick guide A cell close to its tipping point can change shape dramatically from a small change in its membrane.7PubMed Central. Elastic energy of curvature-driven bump formation on red blood cell membrane So shifts in acidity, salt concentration, and chemistry can create burr cells and also reverse them.8Swiss Medical Weekly. The acanthocyte-echinocyte differential
When Burr Cells Are a Lab Artifact, Not a Disease
Red cells keep exchanging water and salts after the blood is drawn.9Kantesti AI. Burr Cells: What Diseases Are They Present In? So blood that waits too long before the slide is made, gets warm, or is spread on a humid or dirty slide can grow even spikes.10Kantesti AI. Burr Cells: What Diseases Are They Present In? An underfilled tube leaves too much anti-clotting chemical for the amount of blood, which can do the same.11Kantesti AI. Burr Cells: What Diseases Are They Present In? Blood stored for a long time in the standard purple-top tube develops burr cells along with other shape changes.12International Journal of Biomedical Science and Engineering. Prolong Storage of Blood in EDTA Has an Effect on the Morphology and Osmotic Fragility of Erythrocytes Slides that dry slowly during manual staining can show burr cells with no medical cause.13Nature, Scientific Data. 1 Million Segmented Red Blood Cells With 240 K Classified in 9 Shapes and 47 K Patches of 25 Manual Blood Smears
Even healthy cells do it. Normal red cells turn into burr-like cells just from touching glass or sitting in warmed plasma, and they can change back.14Free Medical Textbook. ANEMIA OF CHRONIC RENAL FAILURE A few burr cells with otherwise normal results most often reflect the sample.
Artifact burr cells tend to be the only odd finding on an otherwise normal report. A delay between your draw and lab processing, such as a sample sent from a clinic, raises the odds. Repeating the test with a fresh sample made into a slide promptly usually settles it, and it is fair to ask whether the smear was made from fresh blood.
Kidney Failure, Dehydration and Mineral Imbalances
Kidney failure, with waste building up in the blood, changes how red cell membranes work and has long been tied to burr cells.15Kantesti AI. Burr Cells: What Diseases Are They Present In? The link is loose, though: many people with kidney failure have none, and many people with burr cells have healthy kidneys.16Kantesti AI. Burr Cells: What Diseases Are They Present In? Burr cells were once thought characteristic of chronic kidney failure, until it was shown that normal cells make them on glass.17Free Medical Textbook. ANEMIA OF CHRONIC RENAL FAILURE A real kidney cause usually comes with other results on the same panel: rising creatinine and lower kidney filtration estimates, high potassium, and falling hemoglobin from the anemia common in kidney disease. Burr cells alone do not diagnose kidney disease.
Burr cells can also rise with dehydration, including in dehydrated newborns.18Nature, Scientific Data. 1 Million Segmented Red Blood Cells With 240 K Classified in 9 Shapes and 47 K Patches of 25 Manual Blood Smears Dehydration is temporary and fixable, so burr cells from it may fade once you drink and rehydrate. That is why a repeat test after normal fluids is useful.
Red cells need phosphate to make ATP, their energy supply.19PubMed Central. Refeeding Syndrome With Hyperemesis Gravidarum: A Case Report When phosphate falls very low, cells lose flexibility and can become rigid burr cells or round spherocytes.20PubMed Central. Refeeding Syndrome With Hyperemesis Gravidarum: A Case Report These stiff cells break apart early, causing anemia.21PubMed Central. Refeeding Syndrome With Hyperemesis Gravidarum: A Case Report Restoring phosphate prevents or reverses these red cell changes.22The Journal of Laboratory and Clinical Medicine. Severe hypophosphatemia: a frequent complication of hyperalimentation Depletion of salts in the blood is also tied to burr cells.23eClinpath. Quick guide
The classic setting is refeeding syndrome. It happens when someone who has barely eaten for a while starts feeding again quickly, and the body pulls phosphate into cells, dropping blood levels sharply. Dangerously low phosphate can develop within 24 hours when a severely malnourished person starts IV nutrition or eats again.24The Journal of Laboratory and Clinical Medicine. Severe hypophosphatemia: a frequent complication of hyperalimentation It is seen after severe vomiting in pregnancy, with eating disorders, alcohol use, or long hospital fasting. Doctors check phosphate and replace it during refeeding.
Rarer Causes Burns, Venom, Enzyme Defects and Medicines
Pyruvate kinase deficiency is an inherited shortage of an enzyme red cells use to make energy. The cells become misshapen burr cells that the spleen and liver remove early, causing anemia from red cells breaking down early.25Picmonic. Pyruvate Kinase Deficiency It usually shows up in childhood with anemia, jaundice, or an enlarged spleen.
It is present from birth, so the changes tend to persist across tests rather than appear once and vanish. Severity varies widely, and some people have mild forms discovered later in life. Specific enzyme tests confirm it. Burr cells appeared in people with burns over more than about a third of the body, along with a drop in blood fats.26PubMed. Echinocytes and acquired deficiency of plasma lipoproteins in burned patients
Snake bites can cause burr cells that go away on their own in people and dogs.27PubMed. Mechanisms of echinocytosis induced by Crotalus atrox venom Bee, black widow-type spider, and blue-ringed octopus venoms change red cell shape in a lab dish.28PubMed. Sphero-echinocytosis of human red blood cells caused by snake, red-back spider, bee and blue-ringed octopus venoms and its inhibition by snake sera Many venoms contain enzymes that attack the cell membrane.29PubMed. Sphero-echinocytosis of human red blood cells caused by snake, red-back spider, bee and blue-ringed octopus venoms and its inhibition by snake sera
Medicines linked to burr cells include aspirin-type salicylates and the cancer drug doxorubicin, mostly described in animals.30eClinpath. Quick guide Some cancers, such as stomach cancer, have been listed.31Study.com. Burr Cells: Causes & Significance The evidence for drug and cancer links is thin, so they are rarely the explanation. A surprise burr cell in a healthy adult rarely points to these rarer causes.
Burr Cells Versus Spur Cells
Spur cells, also called acanthocytes, have fewer spikes of different lengths spaced unevenly.32Kantesti. Burr Cells: What Diseases Are They Present In? They tend to look dense and shrunken, unlike burr cells.33ASH Image Bank. ACANTHOCYTES IN PERIPHERAL BLOOD SMEAR 1 Telling them apart can be difficult even for experts.34eClinpath. Quick guide Check whether your report says echinocytes or acanthocytes. Mixed forms can appear and carry their own meaning.
The difference comes from the membrane. In a burr cell, the membrane has temporarily puckered, so the cell is changed but still basically a normal disc. In a spur cell, the membrane’s fatty makeup is permanently altered, so the shape is built in. Spur cells come from that built-in defect, while burr cells can be created and reversed by chemistry.35Swiss Medical Weekly. The acanthocyte-echinocyte differential
Spur cells raise concerns like severe liver disease, rare fat-processing disorders, or nerve disorders.36Kantesti. Burr Cells: What Diseases Are They Present In? In severe liver disease, the fats in the blood change and red cell membranes pick up extra cholesterol. That altered membrane gets remodeled as the cells pass through the spleen, leaving the spiky, dense shape. In advanced cirrhosis, especially from alcohol, spur cells can cause serious anemia.37American Journal of Gastroenterology. Unusual Cause Of Severe Anemia In Cirrhosis They usually appear in people who already have clear signs of advanced liver disease, so they are rarely the first clue.
Burr cells are common and usually harmless, while spur cells are uncommon and suggest a serious background problem. A report that mentions spur cells would normally prompt checks of liver function, whereas burr cells often prompt only a repeat test. If your liver tests are abnormal, ask which cell was seen.
What Happens After Burr Cells Show Up
For someone without symptoms who has only a few burr cells and reassuring other results, a fresh blood count with a hand-checked smear in days to a few weeks is usually reasonable.38Kantesti AI. Burr Cells: What Diseases Are They Present In? It should be sooner if creatinine is rising, potassium is high, hemoglobin is falling, or you feel unwell.39Kantesti AI. Burr Cells: What Diseases Are They Present In? No machine reliably spots burr cells yet, so a trained person still checks the slide.40Nature, Scientific Data. 1 Million Segmented Red Blood Cells With 240 K Classified in 9 Shapes and 47 K Patches of 25 Manual Blood Smears
Useful questions for your doctor: Were there few, moderate, or many? Were my kidney, potassium, and phosphate results normal? Could this be from sample delay? Should I repeat the test, and when?
Some symptoms are worth reporting: unusual tiredness or breathlessness suggesting anemia, yellowing skin or eyes, dark urine, and reduced urination or swelling suggesting kidney trouble.
Before a repeat test, drink normally, since dehydration can matter. Mention any recent vomiting, poor eating, or new medicines, and have the blood drawn where the lab processes quickly. Fixing the cause often reverses burr cells.41Swiss Medical Weekly. The acanthocyte-echinocyte differential42PubMed Central. Dynamics of shape recovery by stored red blood cells during washing at the single cell level43PubMed Central. Dynamics of shape recovery by stored red blood cells during washing at the single cell level
If the burr cells are gone on a fresh, promptly made smear, the earlier finding was most likely a handling effect, and no further steps are usually needed. If they persist on a properly handled sample, the clinician looks for a cause using kidney tests, electrolytes, and phosphate. A persistent finding with normal results elsewhere may simply be watched with periodic rechecks.