Complement Activity, Alternative Pathway (AH50)
Ordering Recommendation
Initial screening for suspected deficiency in the alternative complement pathway.
Semi-Quantitative Radial Immunodiffusion
7-14 days  
New York DOH Approval Status
This test is New York DOH approved.
Submit With Order
Specimen Required
Patient Preparation
Serum separator tube or plain red.  
Specimen Preparation
Allow specimen to clot for one hour at room temperature. Separate serum from cells ASAP or within 2 hours of collection. Transfer 1 mL serum to an ARUP Standard Transport Tube and freeze. (Min: 0.3 mL)  
Storage/Transport Temperature
CRITICAL FROZEN. Separate specimens must be submitted when multiple tests are ordered.  
Unacceptable Conditions
Specimen types other than serum. Refrigerated or room temperature specimens. Specimens left to clot at refrigerated temperature. Specimens exposed to repeated freeze/thaw cycles.  
After separation from cells: Ambient: 2 hours; Refrigerated: Unacceptable; Frozen: 2 weeks  
Reference Interval
Effective April 2, 2012

59 percent normal or greater  
Interpretive Data
This test is intended for screening of functional activity of the alternative pathway of the complement system. Abnormal test results can be due to hereditary absence or acquired functional defect in the activity of any of the individual components of the alternative pathway. If test result is abnormal, order specific tests for evaluation of individual components of alternative pathway, including Complement Factor B (ARUP test code 0051720) and Complement Component 3 (ARUP test code 0050150).

Compliance Statement D: This test was developed and its performance characteristics determined by ARUP Laboratories. The U.S. Food and Drug Administration has not approved or cleared this test; however, FDA clearance or approval is not currently required for clinical use. The results are not intended to be used as the sole means for clinical diagnosis or patient management decisions.
CPT Code(s)
Component Test Code*Component Chart NameLOINC
2005374Complement Activity, Alternative Pathway13087-2
* Component test codes cannot be used to order tests. The information provided here is not sufficient for interface builds; for a complete test mix, please click the sidebar link to access the Interface Map.
  • AH50
  • Alternate Pathway
  • Alternative Complement Pathway
  • Alternative Complement Pathway Function
  • Alternative Pathway - Complement
  • Functional Complement
  • Hemolytic Complement