How Anemia Is Diagnosed

Anemia is characterized by a low number of red blood cells (RBCs) and/or defective RBCs that don’t function as they should. Certain physical signs—like pale skin—may provide clues that you have anemia. If you have signs of anemia, a blood test can confirm low RBC concentration and can detect atypical RBCs. Sometimes, the appearance of your RBCs under a microscope can help in pointing to the cause of your anemia. 

Once you are diagnosed with anemia, your medical team may also need further testing to identify the reason for your anemia. Specialized diagnostic studies can distinguish medical issues like low RBC production in your bone marrow or intestinal bleeding. 

Self-Checks/At-Home Testing

You might notice signs of anemia through some self-checks that you can do on your own.

Things you can look for include:

  • Blood in the urine: Blood can appear red or pale pink
  • Blood in the stool: Blood can appear bright red or black and tarry. If you have recurrent gastrointestinal (GI) bleeding, your doctor might recommend an at-home kit for you to use to identify blood in the stool. 
  • Pale or bluish skin and/or lips
  • Cold skin, especially fingers and toes
  • A weak pulse
  • Tachycardia (rapid pulse): A rate above 100 beats per minute is considered fast for an adult. You can count your pulse rate with a stopwatch or your doctor may recommend an at-home pulse monitor. 

Anemia can be dangerous for your health. The signs of anemia can also signal other serious health issues. If you detect any signs of anemia at home, be sure to see your doctor for a full evaluation.

Physical Examination

Whether you have symptoms or not, your doctor will check for anemia on your routine physical examination. Common physical exam abnormalities that can point to possible anemia include: 

  • A weak pulse
  • Tachycardia
  • Pale or bluish skin or lips
  • Cold skin
  • Low blood pressure
  • Postural hypotension (blood pressure that drops when you stand after sitting or lying down)

Many of these physical exam signs may be consistent with the self-test signs you noticed at home on your own. Be sure to let your doctor know when these changes began and whether they are worsening or if they come and go from time to time. 

Labs and Tests

A blood test is the most definitive method of diagnosing anemia, and it can also help in narrowing down the type of anemia. Other lab tests can be used to identify the cause of your anemia. 

Common lab tests used in the diagnostic evaluation of anemia include: 

Complete blood count (CBC): This is the most important test used to detect anemia. It is a standard blood test, and you don’t need any special preparation before having your blood sampled from a vein for your CBC test.

Your report will include your RBC count as well as a description of the size of your RBCs. A low RBC count means that you have anemia. Large RBCs (macrocytic anemia) may indicate vitamin B12 or folic acid deficiency or pernicious anemia. Small RBCs (microcytic anemia) may indicate iron deficiency or bleeding.

Blood smear: A blood smear is a blood sample that is carefully examined under a microscope. This evaluation can provide a description of your RBCs and may identify diseases such as sickle cell anemia. Sometimes a blood smear can identify issues such as hemolytic anemia due to malaria infection or toxins.

A blood smear may also recognize some types of blood cancers such as leukemia and lymphoma, which cause anemia.

Urinalysis (U/A): A urine sample can detect blood in the urine, as well as other problems such as a urinary tract infection or bladder diseases that could lead to anemia.

Occult blood stool sample: Blood loss in the stool due to GI bleeding is a common cause of iron deficiency anemia. A stool sample can be tested for the presence of blood. 

Vitamin B12, folate, or iron level: If your RBCs have an appearance suggestive of a nutritional anemia, you can be tested to verify these nutritional deficits. 

Liver function tests (LFTs): Liver failure or heavy alcohol use can lead to anemia, and LFTs can be used to determine if you have liver disease.

Electrolyte levels: Severe kidney disease and systemic illnesses can lead to anemia. Electrolyte levels can point to many medical illnesses that are associated with anemia. 

Erythropoietin (EPO): A specialized lab test can measure the amount of EPO, a hormone that stimulates the bone marrow to produce RBCs.

Bone marrow biopsy: If there is a strong concern that you may have bone marrow cancer, a bone marrow biopsy can be obtained to verify whether you have this cause of anemia. 

Genetic tests: Some hereditary conditions, such as sickle cell anemia, can cause anemia. This test is a standard part of newborn screening in the U.S. Specialized, non-standard genetic tests that may be needed in your anemia evaluation include a test for thalassemia, hereditary spherocytosis, or glucose 6-phosphate dehydrogenase (G6PD) deficiency.

Colonoscopy or endoscopy: You may need to have an interventional test so that your doctor can view the inside of your GI system to look for areas that could be actively bleeding. Sometimes, these tests detect slow bleeds that are undetectable on imaging tests.

Imaging

Generally, when you are having a medical evaluation to determine the cause of anemia, imaging is used to search for a growth that could be bleeding or a cancerous mass that could be causing anemia.

Your imaging tests would be tailored based on other clues in your physical examination and laboratory evaluation. For example, if you have iron-deficiency anemia with normal iron levels, your imaging tests would be performed to search for possible sources of bleeding. 

Imaging tests used in the evaluation of anemia include: 

  • Abdominal computerized tomography (CT) or magnetic resonance imaging (MRI): These examinations provide pictures of the abdomen and may identify growths or areas of bleeding. 
  • Pelvic ultrasound or CT: This test is used to search for uterine or bladder issues that could be contributing to anemia. 

Differential Diagnoses

Anemia is often a sign of an underlying disease. And since a low RBC count or altered RBCs can be fairly quickly detected with routine blood tests (often even before signs and symptoms of anemia develop), the differential diagnosis is focused on finding the cause or risk factors that led to anemia. 

Common considerations in the differential diagnosis of anemia include:

  • A medication side effect: Many medications can cause anemia as a side effect. The anemia can begin even after you have been taking the medication for years. 
  • Malnutrition due to an undiagnosed intestinal problem such as inflammatory bowel disease (IBD)
  • Malnutrition due to an eating disorder
  • Excessive menstrual bleeding
  • Endometriosis or a uterine fibroid or polyp 
  • GI bleeding
  • Leukemia or lymphoma
  • Cancer of the stomach, small intestine, colon, or liver
  • An infection
  • A hereditary blood disorder

A Word From Verywell

Diagnosis of anemia is a process that involves several objectives, which include identifying your type of anemia as well as the underlying cause. Sometimes the cause isn’t easy to identify, and the diagnostic process can take some time. Once your anemia is diagnosed, you can start on the steps for treatment.

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