Low platelets, a condition called thrombocytopenia, happens when your blood contains fewer than 150,000 platelets per microliter. The causes fall into three broad categories: your bone marrow isn’t making enough platelets, your body is destroying them faster than they can be replaced, or your spleen is trapping too many of them. Sometimes more than one of these problems occurs at the same time.
How Platelet Counts Are Classified
A normal platelet count ranges from 150,000 to 400,000 per microliter of blood. Mild thrombocytopenia (100,000 to 150,000) usually produces no symptoms at all and is often discovered by accident on routine bloodwork. Moderate thrombocytopenia (50,000 to 100,000) can cause easy bruising. Severe thrombocytopenia, below 50,000, raises the risk of bleeding during surgery or injuries. When counts drop below 10,000, spontaneous bleeding becomes a real concern, even without an injury to trigger it.
Your Bone Marrow Isn’t Making Enough
Platelets are produced inside your bone marrow by large cells called megakaryocytes. Anything that damages the marrow or crowds out healthy cells can reduce platelet production.
Blood cancers are a major culprit. In leukemia, lymphoma, and myeloma, abnormal cells multiply inside the bone marrow and physically prevent it from producing healthy blood cells and platelets. Aplastic anemia, a rarer condition where the marrow simply stops working properly, has the same effect.
Cancer treatment is the single most common cause of bone marrow suppression. Chemotherapy drugs are designed to kill fast-dividing cells, but they can’t always distinguish cancer cells from the fast-dividing cells in your marrow. CAR T-cell therapy, a newer type of immunotherapy, can also reduce platelet production as a side effect.
Several viral infections can suppress the marrow directly. These include Epstein-Barr virus, hepatitis C, parvovirus B19, cytomegalovirus, chickenpox, HIV, and dengue fever. In most cases the effect is temporary, but some infections (particularly HIV and hepatitis C) can cause ongoing suppression if untreated.
Nutritional Deficiencies
Your bone marrow needs certain raw materials to build platelets. Deficiencies in vitamin B12 or folate impair the marrow’s ability to produce them. These deficiencies are treatable with supplements or dietary changes, and platelet counts typically recover once the underlying shortage is corrected.
Your Immune System Is Destroying Them
In immune thrombocytopenia (ITP), your immune system mistakenly tags your own platelets for destruction. Your body produces antibodies that attach to proteins on the platelet surface, essentially marking them as foreign invaders. Immune cells in your spleen and liver then recognize these marked platelets and destroy them through a process called phagocytosis.
In roughly 30 to 40 percent of ITP cases, these antibodies can’t be detected on standard tests, suggesting that other parts of the immune system, particularly certain T cells, play a role in the destruction as well. Some of these immune cells migrate into the bone marrow and attack the megakaryocytes directly, reducing new platelet production on top of destroying existing ones.
ITP can be triggered by infections, autoimmune diseases, or situations that disrupt normal immune regulation. There’s a well-documented link between ITP and H. pylori infection, the same bacterium responsible for stomach ulcers. Molecular mimicry is one proposed explanation: proteins on the surface of certain bacteria or viruses closely resemble platelet proteins, so the immune system gets confused and starts attacking both.
Medications That Lower Platelets
Dozens of drugs can cause platelet counts to drop, either by triggering an immune reaction against platelets or by directly suppressing the bone marrow. Heparin, a widely used blood thinner, is the most common cause of drug-induced immune thrombocytopenia. This is a particularly dangerous form because it can paradoxically cause blood clots even as platelet counts fall.
Other medications linked to low platelets include:
- Quinine and quinidine (used for malaria and heart rhythm problems)
- NSAIDs (common over-the-counter pain relievers like ibuprofen)
- Certain antibiotics (penicillin, sulfonamides, linezolid)
- Valproic acid (a seizure medication)
- Statins (cholesterol-lowering drugs)
- Furosemide (a diuretic)
Drug-induced thrombocytopenia usually resolves within days to weeks after stopping the responsible medication.
Your Spleen Is Trapping Too Many
About one-third of all circulating platelets are stored in your spleen at any given time. When the spleen becomes enlarged, a condition called splenomegaly, it traps a much larger share. The platelets aren’t destroyed right away, but they’re effectively removed from circulation, so your bloodwork shows a low count.
Liver cirrhosis is the most common reason for this. Scarring in the liver increases pressure in the blood vessels flowing into the spleen, causing it to swell. Hepatitis and other chronic liver diseases produce the same effect through the same mechanism. In children with sickle cell disease or certain inherited blood disorders like thalassemia, the spleen can suddenly trap a large percentage of total blood volume in what’s called a sequestration crisis, which is a medical emergency.
Low Platelets During Pregnancy
Thrombocytopenia affects 7 to 11 percent of all pregnancies. In about 75 percent of those cases, the cause is gestational thrombocytopenia, a benign condition where platelet counts dip mildly during the second and third trimesters. Counts rarely drop below 70,000, the condition doesn’t affect the baby, and platelets return to normal after delivery without any treatment.
The remaining cases can be caused by more serious pregnancy complications, including preeclampsia and a condition called HELLP syndrome, which involves liver problems and red blood cell breakdown. These require close monitoring and sometimes early delivery.
Signs to Watch For
Mild drops in platelets often produce no noticeable symptoms. As counts fall further, the most recognizable sign is petechiae: tiny pinpoint dots on the skin caused by bleeding from small blood vessels. On lighter skin they appear red or purple. On darker skin tones they may look brown or be harder to spot. Larger areas of skin bleeding are called purpura and resemble bruises that appear without any obvious injury.
Other common signs include nosebleeds that are hard to stop, bleeding gums, blood in urine or stool, and unusually heavy menstrual periods. With very low counts, bleeding can occur internally, which may cause symptoms like severe headaches, vision changes, or abdominal pain depending on the location.
How Low Platelets Are Managed
Treatment depends entirely on the underlying cause. If a medication is responsible, stopping it is often enough. Nutritional deficiencies respond to supplementation. Infections are treated with the appropriate antiviral or antibiotic therapy. ITP may be managed with medications that calm the immune system or, in some cases, with drugs that stimulate the bone marrow to produce more platelets.
Platelet transfusions are reserved for situations where counts are dangerously low. Current international guidelines from 2025 recommend transfusion when platelet counts fall below 10,000 in patients who aren’t actively bleeding. For those undergoing surgery, the threshold is higher: below 50,000 for major operations and below 20,000 for lower-risk procedures like a lumbar puncture. Transfusions provide a temporary boost while the underlying problem is being addressed.