Researchers say that people with anemia—an insufficient number of red blood cells—are more likely to have long-term symptoms of COVID-19 even after the infection has been cleared from the immune system.

A new analysis of Mayo Clinic laboratory testing examines patients who have been rehospitalized due to long-term COVID-19 symptoms. Anemia is the strongest clinical feature of long-term COVID-19 symptoms and may appear weeks or months after the initial infection.

More than 2 billion people worldwide suffer from anemia. The most common causes are low hemoglobin—a protein that helps transport oxygen through the blood to the body’s organs—and the inability to make enough red blood cells. according to Cleveland Clinic.

Iron supplements or dietary changes can usually treat mild anemia, but sometimes red blood cell transfusions are required.

The results of data analysis conducted by the company nference show that when stratifying the risk of COVID-19 patients, laboratory tests related to anemia should be considered.

The research was published in science, Using artificial intelligence software to quickly analyze laboratory tests, clinical records and electronic health records.

“The more we know about the long-term effects of COVID-19 on people who continue to show symptoms weeks and months later, the better we can deal with the new health challenges that this pandemic poses.” Say Venky Soundarajan, co-founder and chief scientific officer of nference.

Dr. Wesley Self, an emergency physician at Vanderbilt University, told us that nearly 30% of COVID-19 patients have long-term complications due to infection ABC News Earlier this year.

The most common symptoms Long-term COVID-19 It is fatigue, fever, dyspnea, depression, myalgia, and damage to the heart, lungs and vascular system.