Test Catalog

Test Id : AH50

Alternative Complement Pathway, Functional, Serum

Useful For
Suggests clinical disorders or settings where the test may be helpful

Investigation of suspected alternative pathway complement deficiency, atypical hemolytic uremic syndrome, C3 glomerulonephritis, dense-deposit disease

Method Name
A short description of the method used to perform the test

Enzyme-Linked Immunosorbent Assay (ELISA)

NY State Available
Indicates the status of NY State approval and if the test is orderable for NY State clients.


Reporting Name
Lists a shorter or abbreviated version of the Published Name for a test

Alternative Complement Path Func, S

Lists additional common names for a test, as an aid in searching

Alternate Pathway


Functional Complement


Alternative Pathway

Specimen Type
Describes the specimen type validated for testing

Serum Red

Ordering Guidance

COM / Complement, Total, Serum and this test are the most appropriate primary assays to use as screening methods for complement deficiencies. Abnormal results in one or the other, neither or both assays will help direct further testing.


This test is rarely useful when ordered in isolation.

Specimen Required
Defines the optimal specimen required to perform the test and the preferred volume to complete testing

Patient Preparation: Patient should be fasting.

Supplies: Sarstedt 5 mL Aliquot Tube (T914)

Collection Container/Tube: Red top (serum gel/SST are not acceptable)

Submission Container/Tube: Plastic vial

Specimen Volume: 1 mL

Collection Instructions:

1. Immediately after specimen collection, place the tube on wet ice.

2. Centrifuge at 4 degrees C and aliquot serum into 5 mL plastic vial.

3. Freeze specimen within 30 minutes.


If not ordering electronically, complete, print, and send a Renal Diagnostics Test Request (T830) with the specimen.

Specimen Minimum Volume
Defines the amount of sample necessary to provide a clinically relevant result as determined by the Testing Laboratory

0.2 mL

Reject Due To
Identifies specimen types and conditions that may cause the specimen to be rejected

Gross hemolysis OK
Gross lipemia OK
Gross icterus OK

Specimen Stability Information
Provides a description of the temperatures required to transport a specimen to the performing laboratory, alternate acceptable temperatures are also included

Specimen Type Temperature Time Special Container
Serum Red Frozen 14 days

Useful For
Suggests clinical disorders or settings where the test may be helpful

Investigation of suspected alternative pathway complement deficiency, atypical hemolytic uremic syndrome, C3 glomerulonephritis, dense-deposit disease

Clinical Information
Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Complement proteins are components of the innate immune system. There are 3 pathways to complement activation:

1. The classical pathway

2. The alternative (or properdin) pathway

3. The lectin (or mannose-binding lectin, MBL) pathway


The total complement (CH50) assay (COM / Complement, Total, Serum) assesses the classical complement pathway including early components that activate the pathway in response to immune complexes (C1q, C2 and C4), as well as the terminal complement components (C3, C5, C6, C7, C8, C9) involved in the formation of the membrane attack complex (MAC). The CH50 assay will be abnormal if there are specific hereditary or acquired C1-C9 complement component deficiencies or if there is consumption of complement due to immune (or autoimmune) complexes.


This assay is a screening test for complement abnormalities in the alternative pathway. The alternative complement (AH50) pathway shares C3 and C5-C9 components but has unique early complement components designated factors D, B, and properdin, as well as control proteins factor H and factor I. This pathway can be activated by spontaneous hydrolysis of C3 or by microbial polysaccharides and does not require immune complex formation. Patients with disseminated infections with pyogenic bacteria in the presence of a normal CH50 may have a decreased AH50 due to hereditary or acquired deficiencies of the alternative pathway. Patients with deficiencies in the alternative pathway factors (D, B, properdin, H, and I) or late complement components (C3, C5-C9) are highly susceptible to recurrent Neisserial meningitis. The use of the CH50 and AH50 assays allow identification of the specific pathway abnormality.


Functional testing for complement pathways activity is indicated in the study of complement components deficiency, where testing serves as a first-tier screening, or in the study of complement dysregulation. Complement dysregulation is a general grouping of complement conditions where there is loss of control of the complement cascade with over-activation. In several cases, the complement system will attack the host and the over-activation of the complement cascade may cause disease.


Over-activation of the alternative pathway usually presents with renal function impairment, in rare conditions such as atypical hemolytic uremic syndrome and C3 glomerulopathies (dense deposit disease and C3 glomerulonephritis).


The use of complement inhibitor therapies such as eculizumab and ravulizumab will result in the blocking of C5. C5 is necessary for the AH50 test to progress until the formation of the MAC. Hence, in the presence of eculizumab or ravulizumab, AH50 results will be decreased or undetectable.

Reference Values
Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

> or =46% normal

Provides information to assist in interpretation of the test results

Absent complement alternative pathway (AH50) in the presence of a normal total hemolytic complement (CH50) suggests an alternative pathway component deficiency.


Normal AH50 with absent CH50 suggests an early (C1, C2, C4) classic pathway deficiency.


Absent AH50 and CH50 suggests a late (C3, C5, C6, C7, C8, C9) component deficiency or complement consumption.


Absent AH50 and CH50 in the presence of a normal C3 and C4 suggests a late (C5, C6, C7, C8, C9) component deficiency.


Normal CH50 and AH50 in the presence of recurrent infection and continued suspicion of complement deficiency, suggest testing for lectin pathway function.

Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

This assay is a functional test and is dependent on correct sampling, storage, and shipping conditions. Both degradation by temperature and consumption of complement components will lead to false low function results. These are difficult to differentiate from real complement dysregulation.


While preanalytic handling can lead to false-positive results, it is far less likely that it would lead to false-normal results. If more than one component is measured as low, it is important to look for technical errors.


Complement testing may be ordered in several circumstances where standard treatment includes plasmapheresis or plasma exchange. The procedure itself, if traumatic, may activate complement so may not reflect what is going on with the patient's complement system. The recommendation is to collect blood prior to the plasma exchange whenever possible.


Functional results inconsistent with the clinical history should be verified with a new blood draw.


Specimens should be frozen immediately after collection.


Long term stability is optimal when the sample is kept at -70 degrees Celsius or lower prior to testing.

Clinical Reference
Recommendations for in-depth reading of a clinical nature

1. Frank MM: Medical intelligence current concepts: complement in the pathophysiology of human disease. N Engl J Med. 1987;316:1525-1530. doi: 10.1056/NEJM198706113162407

2. Thurman JM, Holers VM: Brief reviews: the central role of the alternative complement pathway in human disease. J Immunol. 2006;176:1305-1310. doi: 10.4049/jimmunol.176.3.1305

3. Frank MM: Complement deficiencies. Pediatr Clin North Am. 2000;47(6):1339-1354. doi: 10.1016/s0031-3955(05)70274-1

4. Go RS, Winters JL, Leung N, et al: Thrombotic microangiopathy care pathway: A consensus statement for the Mayo Clinic Complement Alternative Pathway-Thrombotic Microangiopathy (CAP-TMA) Disease-Oriented Group. Mayo Clin Proc. 2016;91(9):1189-1211. doi: 10.1016/j.mayocp.2016.05.015

5. Willrich MAV, Andreguetto BD, Sridharan M, et al: The impact of eculizumab on routine complement assays. J Immunol Methods. 2018;460:63-71. doi: 10.1016/j.jim.2018.06.010

Method Description
Describes how the test is performed and provides a method-specific reference

The Wieslab enzyme-linked immunosorbent assay (ELISA) complement assay for the alternative pathway combines principles of the hemolytic assay for complement activation with the use of labeled antibodies specific for neoantigens produced as a result of complement activation. The micro titer plate strips are coated with lipopolysaccharide. Patient serum is diluted in diluent containing specific blocker to ensure that only the alternative pathway is activated. During the first incubation, the diluted patient serum in the wells is activated by the coating. The wells are then washed and C5b-9 (membrane attack complex: MAC) is detected with a specific alkaline phosphatase labeled antibody to the neoantigen expressed during MAC formation. After a final wash, an alkaline phosphatase substrate is added. The amount of alternative pathway complement activity correlates with the color intensity of the solution and is measured in terms of absorbance (optical density).(Frazer-Abel A, Sepiashvili L, Mbughuni MM, Willrich MA: Overview of laboratory testing and clinical presentations of complement deficiencies and dysregulation. Adv Clin Chem. 2016;77:1-75. doi: 10.1016/bs.acc.2016.06.001)

PDF Report
Indicates whether the report includes an additional document with charts, images or other enriched information


Day(s) Performed
Outlines the days the test is performed. This field reflects the day that the sample must be in the testing laboratory to begin the testing process and includes any specimen preparation and processing time before the test is performed. Some tests are listed as continuously performed, which means that assays are performed multiple times during the day.

Monday, Thursday

Report Available
The interval of time (receipt of sample at Mayo Clinic Laboratories to results available) taking into account standard setup days and weekends. The first day is the time that it typically takes for a result to be available. The last day is the time it might take, accounting for any necessary repeated testing.

3 to 5 days

Specimen Retention Time
Outlines the length of time after testing that a specimen is kept in the laboratory before it is discarded

14 days

Performing Laboratory Location
Indicates the location of the laboratory that performs the test


Several factors determine the fee charged to perform a test. Contact your U.S. or International Regional Manager for information about establishing a fee schedule or to learn more about resources to optimize test selection.

  • Authorized users can sign in to Test Prices for detailed fee information.
  • Clients without access to Test Prices can contact Customer Service 24 hours a day, seven days a week.
  • Prospective clients should contact their account representative. For assistance, contact Customer Service.

Test Classification
Provides information regarding the medical device classification for laboratory test kits and reagents. Tests may be classified as cleared or approved by the US Food and Drug Administration (FDA) and used per manufacturer instructions, or as products that do not undergo full FDA review and approval, and are then labeled as an Analyte Specific Reagent (ASR) product.

This test was developed, and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the US Food and Drug Administration.

CPT Code Information
Provides guidance in determining the appropriate Current Procedural Terminology (CPT) code(s) information for each test or profile. The listed CPT codes reflect Mayo Clinic Laboratories interpretation of CPT coding requirements. It is the responsibility of each laboratory to determine correct CPT codes to use for billing.

CPT codes are provided by the performing laboratory.


LOINC® Information
Provides guidance in determining the Logical Observation Identifiers Names and Codes (LOINC) values for the order and results codes of this test. LOINC values are provided by the performing laboratory.

Test Id Test Order Name Order LOINC Value
AH50 Alternative Complement Path Func, S 74520-8
Result Id Test Result Name Result LOINC Value
Applies only to results expressed in units of measure originally reported by the performing laboratory. These values do not apply to results that are converted to other units of measure.
88676 Alternative Complement Path Func, S 74520-8

Test Setup Resources

Setup Files
Test setup information contains test file definition details to support order and result interfacing between Mayo Clinic Laboratories and your Laboratory Information System.

Excel | Pdf

Sample Reports
Normal and Abnormal sample reports are provided as references for report appearance.

Normal Reports | Abnormal Reports

SI Sample Reports
International System (SI) of Unit reports are provided for a limited number of tests. These reports are intended for international account use and are only available through MayoLINK accounts that have been defined to receive them.

SI Normal Reports | SI Abnormal Reports