Objective To observe the late effects of hematopoietic system damage in patients with a bone marrow form of acute radiation sickness (ARS) and to explore the rules and influencing factors of distant posterior changes in the hematopoietic system after acute irradiation.

Methods Clinical follow-up was conducted on two patients with moderate bone marrow form of ARS ("Tian" and "Wang", both male, aged 37 and 8 years, respectively) and one patient with severe bone marrow form of ARS ("Mei", female, 38 years old) during the "4.26" ⁶⁰Co radiation accident in Henan Province in 1999. The follow-up period was until 2019 with a total of 11 times. According to the Standard in Medical Follow-up of the Long-Term Effects of Acute Radiation Sickness by External Irradiation, the peripheral blood and bone marrow of 3 patients were collected regularly for peripheral hemogram, bone marrow smear, bone marrow progenitor cell culture, and hematopoietic stimulating factor examination from half a year after irradiation until 2019. (1) Peripheral hemogram examination: automatic blood cell analyzer was used to analyze white blood cell (WBC), platelet (PLT), and red blood cell counts; hemoglobin (Hb) level; and neutrophil (NEUT) and lymphocyte (LYM) percentages in peripheral blood. (2) Bone marrow aspiration examination: bone marrow smear and hematopoietic progenitor cell culture were performed to detect colony-forming unit-erythroid (CFU-E), burst-forming unit-erythrocytic(BFU-E), colony forming unit-granulocyte–monocyte (CFU-GM). (3)Hematopoietic stimulating factor examination: erythropoietin (EPO) and granulocyte-macrophage colony-stimulating factor (GM-CSF) were detected.

Results During the 20-year follow-up, the WBC counts of all three patients were within the normal range. The percentages of LYM were low, and those of NEUT were high half a year after irradiation. During the follow-up period, "Mei" repeatedly had increased NEUT percentage, and "Wang" repeatedly showed abnormal LYM and NEUT percentages. The PLT counts of "Mei" decreased slightly to 80×10⁹/L and 91×10⁹/L respectively in half a year and the first year after irradiation. A half year after irradiation, the PLT count of "Wang" decreased slightly to 91×10⁹/L, whereas that of "Tian" was normal. The Hb level of "Mei" decreased slightly several times and moderately decreased to 85 g/L in the fifth year after irradiation. The Hb level of "Tian" increased abnormally in the ninth year after irradiation, and the Hb levels of "Tian" and "Wang" increased or decreased slightly several times during the follow-up period. The results of the six bone marrow biopsy smears of all three patients showed active or remarkably active myelodysplastic during the follow-up period. The CFU-E, BFU-E, and CFU-GM levels of the three patients increased abnormally half a year after irradiation, decreased to 0 in the second year, and then recovered slowly in the seventh year. The CFU-Es of the three patients were higher than the normal range, the CFU-GMs almost recovered, and the BFU-Es still decreased considerably. In the first three years of follow-up, the EPOs of "Tian" were slightly abnormal in half a year and the first year, whereas those of "Mei" and "Wang" were within the normal range. Half a year after irradiation, the GM-CSF levels of the three patients were all less than 1.00 pg/mL. The GM-CSF level of "Mei" increased abnormally to 14.3 pg/mL in the first year and returned to normal in the second year. "Tian" and "Wang" had normal GM-CSF levels in the first and second years.

Conclusions Hematopoietic system damage by acute irradiation is dose dependent and long term. Hematopoietic stimulating factor has a long-term effect on the recovery of bone marrow hematopoietic function. No consistent change was observed among the indexes that reflect the recovery of bone marrow hematopoietic function, which needs comprehensive evaluation during medical follow-up.