When both your red and white blood cell counts are low at the same time, it signals that your body isn’t producing enough blood cells or is destroying them faster than normal. Doctors call this “bicytopenia,” meaning two of the three major blood cell lines (red cells, white cells, and platelets) are reduced. It’s not a diagnosis on its own but a lab finding that points toward an underlying cause, ranging from something as treatable as a vitamin deficiency to more serious conditions like bone marrow disorders.
What Counts as “Low”
A complete blood count (CBC) is the standard blood test that measures these cells. Normal red blood cell counts range from 4.35 to 5.65 trillion cells per liter in men and 3.92 to 5.13 trillion in women. For white blood cells, the normal range is 3.4 to 9.6 billion cells per liter for all adults. Falling below these ranges on a single test doesn’t always mean something is wrong, since temporary fluctuations happen. But consistently low numbers in both cell types warrant further investigation.
Anemia, the clinical term for low red blood cells, is formally diagnosed when hemoglobin drops below 13.6 g/dL in men or below 12 g/dL in women. Low white blood cell count is called leukopenia. When both show up together, your doctor will likely want to figure out why your bone marrow, the factory where all blood cells are made, isn’t keeping up.
How It Feels When Both Are Low
Low red blood cells reduce the oxygen your tissues receive. The most common symptom is extreme tiredness that doesn’t improve with rest. You might also notice shortness of breath during activities that didn’t used to wind you, pale skin, dizziness, or cold hands and feet.
Low white blood cells weaken your immune defenses, making you more vulnerable to infections. Fever and chills are the hallmark signs. You might find yourself catching colds or other illnesses more frequently, and minor infections may take longer to clear or become unusually severe. Some people develop mouth sores or skin infections that seem out of proportion to the cause.
When both counts drop together, these symptoms overlap. You can feel exhausted and sick at the same time, which is what often prompts people to see a doctor and get the blood test that reveals the problem.
Nutritional Deficiencies
One of the most common and most fixable causes is a shortage of vitamin B12 or folate. Both nutrients are essential for DNA synthesis and the maturation of new blood cells. Without enough of either one, your bone marrow can’t produce red or white cells efficiently. The cells it does make are often abnormally large, a condition called macrocytic anemia.
B12 deficiency is especially common in older adults, vegetarians and vegans, and people with digestive conditions that impair absorption (like celiac disease or Crohn’s disease). Folate deficiency can result from poor diet, heavy alcohol use, or certain medications. In severe cases, combined B12 and folate deficiency can drop all three blood cell lines low enough to mimic bone marrow failure on lab tests, even though the underlying problem is purely nutritional. Supplementation typically reverses the counts over weeks to months.
Infections That Suppress Blood Counts
Several viruses can directly interfere with blood cell production by infecting the bone marrow or triggering immune responses that destroy circulating cells. HIV is one of the best-known examples, often causing low counts across multiple cell lines as the disease progresses. Hepatitis B and C, Epstein-Barr virus (the virus behind mono), and cytomegalovirus (CMV) can all suppress marrow output.
These viral effects are sometimes temporary. A bad flu or other acute infection can transiently lower your counts, which bounce back once you recover. But chronic viral infections like HIV or hepatitis C can cause sustained drops that need ongoing management. Dengue virus and parvovirus B19 are also known triggers, particularly in people with weakened immune systems.
Bone Marrow Disorders
Your bone marrow is where red cells, white cells, and platelets are all manufactured. When the marrow itself is damaged or dysfunctional, production of multiple cell types drops simultaneously. This is what doctors look for when simpler explanations have been ruled out.
Aplastic anemia is one key condition in this category. The marrow becomes underactive and stops producing enough cells. It can be triggered by autoimmune attacks, toxic chemical exposure, radiation, or sometimes occurs with no identifiable cause. Myelodysplastic syndromes (MDS) are another group of disorders where the marrow produces blood cells that are abnormal and don’t function properly. MDS occurs more often in older adults and can, in some cases, progress to leukemia.
Inherited bone marrow failure syndromes, though rare, can also cause low counts. These are genetic conditions typically diagnosed in childhood. Fanconi anemia, for instance, usually produces progressively worsening blood counts during childhood and carries an increased risk of developing leukemia later. These conditions are uncommon but important to identify because they require specialized monitoring and treatment plans.
Medications and Cancer Treatment
Chemotherapy is the most common drug-related cause of simultaneous low red and white blood cells. These drugs work by killing rapidly dividing cells, and bone marrow cells divide rapidly, so they’re collateral damage during cancer treatment. Most patients receiving chemotherapy experience some degree of bone marrow suppression, called myelosuppression.
Newer cancer treatments like CAR T-cell therapy, a type of immunotherapy, can also reduce blood cell and platelet production. Outside of cancer treatment, certain antibiotics, anti-seizure medications, and drugs used for autoimmune conditions can occasionally suppress marrow function as a side effect. If your low counts appeared after starting a new medication, that connection is worth discussing with your doctor.
Autoimmune Conditions
Sometimes the immune system mistakenly targets blood cells for destruction. Lupus (systemic lupus erythematosus) is one of the more common autoimmune diseases associated with low blood counts across multiple cell types. The immune system produces antibodies that attack red cells, white cells, or both.
Evans syndrome is a rarer autoimmune disorder where the body destroys its own red blood cells and platelets, and in some cases white blood cells too. It can affect both children and adults. The hallmark is that the destruction is immune-driven rather than caused by a production problem in the marrow, which changes how it’s treated.
How Doctors Find the Cause
The CBC that revealed your low counts is just the starting point. Your doctor will typically look at the size and shape of your blood cells under a microscope using a peripheral blood smear. Very small red cells suggest iron deficiency or a genetic hemoglobin disorder, while very large red cells (with a mean corpuscular volume above 120) point toward B12 or folate deficiency.
Blood tests for B12, folate, iron levels, and markers of inflammation or infection often come next. If these don’t explain the low counts, or if the pattern is concerning, a bone marrow biopsy may be recommended. This involves taking a small sample of marrow, usually from the back of the hip bone, and examining it under a microscope. It remains the definitive test for diagnosing marrow disorders like aplastic anemia or MDS. Genetic testing on blood samples is increasingly used alongside biopsies to detect specific mutations that help classify the problem and guide treatment decisions.
The diagnostic path depends heavily on your age, other symptoms, how low the counts are, and how quickly they dropped. A mild dip in someone who just recovered from a viral illness gets a very different workup than a significant drop in someone with unexplained weight loss or recurrent infections.