Plasma Factor D Level
C3 Glomerulopathy and atypical Hemolytic Uremic Syndrome

Factor D (FD), also known as adipsin, is a 24 kDa serine protease predominantly produced by adipocytes. Its sole function is to cleave its natural substrate, C3b-bound factor B (FB), thereby generating C3bBb and activating the amplification loop of the alternative pathway (AP) of complement. Plasma FD levels in healthy individuals can vary but under normal conditions are within the range of 1–2 μg/mL. Due to its small size, FD is filtered through the glomerulus and then reabsorbed within the renal tubules. In patients with chronic kidney disease secondary to C3G and aHUS, factor D levels can be elevated up to 30-fold above normal. FD concentration can impact the activity of the AP and its elevation can serve as a secondary driver of complement dysregulation.

This test has been incorporated into these panels: C3 Glomerulopathy Complement Panel (C3G-CP); aHUS (complement-mediated TMA) Functional Panel (aHUS-FP); and the Complement Biomarker Panel (CBP). This test is also available a la carte.

Indications for screening 
Testing is recommended for patients with C3G and aHUS

MORL screening methodology 
Enzyme Linked Immuno-Sorbent Assay (ELISA)

Turnaround time 
Turnaround time is ~3 weeks

Sample Required 
1 ml frozen EDTA plasma (see page 3of Kidney Testing Requisition for specimen processing and shipping requirements).

Cost & CPT Codes

The Clinical Diagnostics Service of the Molecular Otolaryngology & Renal Research Laboratories is a CLIA-approved, Joint Commission-accredited diagnostic laboratory.