To investigate the diagnostic value of serum complement components 1 q (C1q), neutrophil gelatinase-associated lipocalin (NGAL), cystatin C (CysC), creatinine (SCr) and urea (SUr) for early diabetic kidney disease (EDKD)

Material and methods:
Individuals with type 2 diabetes mellitus (DM) and healthy subjects at Mianyang Central Hospital from March, 2017 to November, 2017 were enrolled according to the inclusion and exclusion criteria. Serum SUr, SCr, CysC, C1q and NGAL were detected. Diagnostic values were evaluated by ROC.

Totally, 546 individuals were enrolled, including 136 patients in simple DM group (SDM group), and 109 patients in EDKD group and 301 healthy controls (HC group). Compared with SDM group and HC group, serum SUr, SCr, C1q, CysC and NGAL in EDKD group were significantly increased (P<0.01). C1q, CysC, and NGAL were significantly related to EDKD and they were risk factors for EDKD. Diagnostic performance of CysC (AUC=0.813, 0.777~0.845), C1q (AUC=0.797, 0.761~0.830) or NGAL (AUC=0.770, 0.732~0.805) was much higher than that of SCr (AUC=0.681, 0.640~0.720) or SUr (AUC=0.650, 0.608~0.690) (p < 0.05). C1q +CysC (AUC=0.896, 0.867~0.920; Se=77.98%, 74.27% - 81.39%; Sp=89.4%, 86.59% - 91.92%; YI=0.675) had the optimal diagnostic performance. However, combination of C1q+CysC+NGAL (AUC=0.909, 0.882~0.932; Se=88.99%, 86.06% - 91.49%; Sp=80.32%, 76.73% - 83.57%; YI=0.693) or C1q+CysC+NGAL+SCr (AUC=0.912, 0.885~0.934; Se=87.16%, 84.06% - 89.85%; Sp=83.98%, 80.63% - 86.96%; YI=0.711) did not further improve diagnosis performance for EDKD (p>0.05).

C1q, CysC and NGAL have similar diagnostic performances, which is superior to SCr, in diagnosis of EDKD. Moreover, C1q +CysC combination has the optimal diagnostic performance for EDKD.