Serum folate vs red blood cell folate

This is the 4365th article of Da Yi Xiao Hu

Folic acid is widely found in plants and animal livers, and is particularly rich in green leafy vegetables. Overcooking food can destroy the folic acid in it. Folic acid deficiency leads to disorders in the synthesis of red blood cell DNA, stagnation of the development of the cell nucleus, while the cytoplasm continues to mature, and the cell volume is larger than normal, so it is called megaloblasts - "giant baby" red blood cells with maturation disorders but huge volume.

Elderly people like to eat soft and rotten food due to tooth loss, so they will steam and cook the food for a long time when processing it, which causes the folic acid in the food to be destroyed. In the long run, folic acid deficiency will lead to megaloblastic anemia, which is manifested by pale complexion, loss of appetite, listlessness, memory loss or forgetfulness, and sometimes local skin numbness. In severe cases, dementia may occur; scaly papules or plaques appear on the extensor side of the limbs, showing seborrheic dermatitis-like changes, and will be accompanied by cheilitis, glossitis, atrophy of the tongue papillae, smooth surface, and pain.

Pregnant women are also at high risk of folic acid deficiency, especially megaloblastic anemia, which is manifested as fatigue, poor appetite, inattention, numbness of hands and feet, sensory impairment, dry and yellow hair, dull complexion, and poor mental state. In addition to the adverse effects on pregnant women themselves, it can also lead to fetal growth retardation, mental retardation, and even neural tube defects and cleft lip. Moreover, even after the fetus is born, it will still be mentally depressed and growth and development will continue to be slow, leading to extreme malnutrition.

Methods for determining folic acid in patients with megaloblastic anemia include chemiluminescence, microbial modified determination, radioimmunoassay, absorption test, histidine load test, etc. Different methods can be selected clinically according to different needs. Due to the differences in the detection capabilities of calibrators and folic acid derivatives used by different manufacturers, the same sample may produce inconsistent results using the detection systems of different manufacturers. The test results of different laboratories should be interpreted with caution in the clinic, and the use of the same reference standard can reduce the differences in results between methods.

Clinical testing of folic acid is mainly divided into two types: serum testing and red blood cell testing. Serum folate levels are affected by folic acid intake. If folic acid intake is insufficient, serum folate concentrations will decrease within 3 weeks, while red blood cell folate levels can remain stable for 3-4 months. Red blood cell folate levels can better reflect the body's folate reserves and are recognized as a better folate indicator. Therefore, it is recommended to measure serum and red blood cell folate at the same time to more accurately reflect the body's overall folate level and tissue folate level. The relationship between the two is similar to that of blood sugar and glycated hemoglobin. Blood sugar reflects the immediate blood sugar level in the body, while glycated hemoglobin reflects the blood sugar level over a period of time.

Elevated serum folate may be seen in pernicious anemia, long-term vegetarians, and intestinal blind loop syndrome; decreased serum folate may be seen in megaloblastic anemia, hemolytic anemia, myeloproliferative disease, normal pregnancy, hyperthyroidism, malnutrition, alcoholism, malignant tumors, and liver disease.

Decreased red blood cell folate is mainly used for megaloblastic anemia, rapid growth and insufficient folate supply, and normal pregnancy; regular use of medications such as methotrexate, phenytoin sodium, primidone, pyrimethamine, and isoniazid can also lead to decreased folate.

Because serum folate levels are easily changed with food intake, fasting blood tests are required; those who take antibiotics or contraceptives should stop taking them for 1 week before testing, and drinking is prohibited before blood collection.

Author: Hematology Hospital, Chinese Academy of Medical Sciences

Wang Hailong Attending Physician