Fibrinogen (FIB) is often elevated in children with Henoch Schonlein purpuric nephritis (HSPN), but the correlation between FIB and renal lesions has been less studied.

To explore the correlation between FIB in children with HSPN and the International Study Group on Pediatric Kidney Disease (ISKDC) pathology grading and micropathological changes in parts of renal units, and to clarify whether FIB can assess the severity of renal injury in children with HSPN.

In total, 922 children with HSPN who were hospitalized in the First Affiliated Hospital of Henan University of Chinese Medicine in the pediatric nephrology ward and underwent kidney biopsy at the same time from December 2017 to December 2022 were collected, and the clinical information, FIB and renal pathological information during renal biopsy were summarized, and based on the FIB level, the children were categorized into group A (low) <2.38 g/L, group B (standard) 2.38-4.98 g/L, and group C (high) >4.98 g/L. The correlation between FIB and ISKDC pathological grades, glomerular mesangial hyperplasia ratio, the crescentic bodies ratio and the nature of the glomerular lesions from acute to chronic was investigated by Spearman rank correlation analysis, and the prediction of FIB on the micropathological changes of renal units was analyzed by the subject's work characteristic (ROC) curve.

Among 922 children with HSPN who had undergone renal biopsy, the FIB was (3.48±1.01) g/L. 113 cases in group A had a low FIB rate of 12.26%; 734 cases in group B had a standardized FIB rate of 79.61%; and 75 cases in group C had a high FIB rate of 8.13%. The ISKDC pathology classification was type Ⅱa in 173 cases (18.76%), type Ⅱb in 29 cases (3.15%), 466 cases (50.54%) of type Ⅲa, 232 cases (25.16%) of type Ⅲb, and 22 cases (2.39%) of type Ⅳ and above (including 2 cases of type Ⅳa, 18 cases of type Ⅳb, and 2 cases of type Ⅴ). The results of the Spearman's rank correlation analysis showed that the FIB and the grouping of the FIB of the children with HSPN were positively related to the renal pathology ISKDC grading (r_s=0.146, P<0.001; r_s=0.129, P<0.001). 911 (98.80%) of 922 children with HSPN were mesangial proliferative, and 655 (71.04%) had crescentic hyperplasia. Spearman rank correlation analysis showed a weak positive correlation between FIB and FIB subgroups and the rate of mesangial hyperplasia (r_s=0.092, P=0.005; r_s=0.096, P=0.003), and a positive correlation with the rate of crescentic bodies (r_s=0.132, P<0.001; r_s=0.830, P=0.012). 922 children with HSPN had glomerular acute lesions in 763 cases (82.75%), acute chronic lesions in 97 cases (10.52%), and chronic lesions in 62 cases (6.73%). In addition, FIB gradually increased with the nature of the glomerular lesions from acute to chronic (r_s=0.145, P<0.001). At the same time, comparison of some renal biopsy indexes FIB in HSPN children showed statistically significant difference (P<0.05). The ROC curves showed that the FIB had the highest sensitivity for glomerulosclerosis (sensitivity=0.900, specificity=0.303), and the optimal cutoff value for FIB was 2.835 mg/L; the area under the ROC curve (AUC) of FIB for the positive prediction of tubulointerstitial fibrosis=0.623, and that of FIB for the reverse prediction of tubulointerstitial cellular granulomatous degeneration=0.641.

FIB can be used as a laboratory index reflecting the severity of renal pathological changes in patients with HSPN, can reflect the severity of renal pathological grading, is closely related to irreversible lesions according to renal microscopic indicators such as glomerular sclerosis and balloon adhesion, and can assist clinical diagnosis and treatment.