Skip directly to site content Skip directly to search


Español  Other Languages


Centers for Disease Control and Prevention. CDC twenty four seven. Saving Lives, Protecting People
 Search
		×
			Vaccines site
			Vaccines site
				All CDC
				Submit
			For a full list of topics:A-Z Index
			Advanced Search
		Advanced Search


Vaccines & Immunizations


Section Navigation
			
			CDC Home








Lab Tests to Collect Shortly After Severe Allergic Reaction/Anaphylaxis Following COVID-19 VaccinationFor Healthcare Providers						Print
																Related Pages
										**This web page is archived for historical purposes and is no longer being updated. Please go to CDC Home or use the A-Z Index or Search for more recent information.**
There are no specific lab tests that can definitively diagnose the cause of a severe allergic reaction (e.g., anaphylaxis) following COVID-19 vaccination. In the United States, two commercially available lab tests can be ordered by healthcare providers and processed through healthcare facilities to better characterize a severe allergic reaction.
This document provides an overview of the timing and procedure for collecting blood samples for these lab tests. These samples should only be collected after medically stabilizing a patient who has experienced a severe allergic reaction.
**The two commercially available lab tests are**:
Tryptase (a mast cell marker)
SC5b-9 (terminal complement complex)Tryptase is released from mast cells during anaphylaxis. SC5b-9 (terminal complement complex) is a measurement of complement system activation. These lab tests can be transiently elevated shortly after a severe allergic reaction. Elevations in these test results can help characterize the severe allergic reaction. Therefore, the timing of the blood sample collection for these tests can affect interpretation of the results.
The ideal time window to collect blood for these two tests is between 30 minutes and 90 minutes after the reaction began. However, these blood tests might still remain elevated up to 6 hours after the reaction began.
Collecting blood earlier than 30 minutes after the reaction began could yield results that would be more difficult to interpret.
If unable to collect this blood within the ideal 30–90 minute time window after the reaction began, healthcare providers can collect the blood samples as soon as possible, up through 6 hours after the reaction.
These results are unlikely to be affected by epinephrine, antihistamines, and other treatments used to manage anaphylaxis.Healthcare providers can consult with the laboratory in their healthcare facility to determine their site-specific practice for processing samples for tryptase and SC5b-9 tests. Typically, immediately flash-freezing the serum sample for SC5b-9 at -80 degrees C can maximize the accuracy of this test. The resources below provide more information about specimen processing requirements for some commercial laboratories. CDC does not endorse a particular laboratory.
A second sample for tryptase could be obtained 24 hours or more after the severe allergic reaction, or even weeks after the reaction. This tryptase level obtained 24 hours or more after the severe allergic reaction reflects the patient’s typical tryptase level and can aid in the assessment of the allergic reaction.
Interpreting test results
Interpretation of these test results can be challenging. Consultation with a specialist (e.g., allergist-immunologist) within the weeks after the severe allergic reaction can help healthcare providers further evaluate potential factors that might have contributed to the development of the allergic reaction in these individuals. Also, healthcare providers or health departments in the United States can request a consultation from **CISA COVIDvax** for a complex COVID-19 vaccine safety question that is (1) about an individual patient residing in the United States or vaccine safety issue and (2) not readily addressed by CDC or Advisory Committee on Immunization Practices (ACIP) guidelines. More information about how to request a CISA COVIDvax consultation is available here: Clinical Immunization Safety Assessment (CISA) Project.
Reporting errors and adverse events
Vaccination providers are required by the Food and Drug Administration to report vaccination administration errors, serious adverse events, cases of Multisystem Inflammatory Syndrome, and cases of COVID-19 that result in hospitalization or death following COVID-19 vaccination under Emergency Use Authorization. Reporting is encouraged for any other clinically significant adverse event even if it is uncertain whether the vaccine caused the event. For information on how to submit a report to the Vaccine Adverse Event Reporting System (VAERS) click here or call 1-800-822-7967.Additional ResourcesTryptase | ARUP Lab Test Directory
Tryptase | Labcorp
Tryptase | Quest Diagnostics
SC5b-9 Level Terminal Complement Complex | Quest Diagnostics
SC5b-9 Level – Terminal Complement Complex | Diagnostic Testing | Clinical Laboratory (nationaljewish.org)
Interim Clinical Considerations for Use of COVID-19 Vaccines Currently Authorized in the United States | CDC
Interim Considerations: Preparing for the Potential Management of Anaphylaxis at COVID-19 Vaccination Sites | CDC
							
					
							Last Reviewed:  August 9, 2021						Source: 	National Center for Immunization and Respiratory Diseases
					Facebook
        Twitter
        LinkedIn
        Syndicate homeCOVID-19 Vaccination
Product Info by U.S. Vaccineplus icon
EUA
EUI
Interim Clinical Considerationsplus icon
Use of COVID-19 Vaccines in the U.S.
Use of COVID-19 Vaccines in the U.S.: Appendices
FAQs for the Interim Clinical Considerations
Myocarditis and Pericarditis Considerations
Clinical Care
Provider Requirements and Support
Vaccine Recipient Educationplus icon
Talking with Patients about COVID-19 Vaccination
How to Tailor COVID-19 Information to Your Audience
How to Address COVID-19 Vaccine Misinformation
Health Departments
Planning & Partnerships
6 Things to Know
Equity in Childhood COVID-19 Vaccination
COVID-19 Vaccine Data Systemsplus icon
Overviewplus icon
Vaccine IT Overview
Data Reporting Requirements
Vaccine Administration Management System (VAMS)plus icon
Getting Started in VAMS
General Public User
Resources for Jurisdictions, Clinics, and Organizations
VAMS Program Information
Vaccinate with Confidenceplus icon
What Is Vaccine Confidence?
Vaccine Confidence Strategies
Rapid Community Assessment Guide
COVID-19 Vaccine Confidence Data
12 COVID-19 Vaccination Strategies for Your Community
How to Engage the Arts to Build COVID-19 Vaccine Confidence
Strategies for Reaching People with Limited Access to COVID-19 Vaccines


About CDC
					Contact Us
					800-232-4636
 Facebook Twitter Instagram LinkedIn Youtube Pinterest Snapchat
 CONTACT CDC
				Contact Us
							Call 800-232-4636
							Email Us
			ABOUT CDC
				About CDC
							Jobs
							Funding
			POLICIES
				Accessibility
							External Links
							Privacy
							Policies
							No Fear Act
							FOIA
							OIG
							Nondiscrimination
							Vulnerability Disclosure Policy
			CONNECT WITH US
				Facebook
								Twitter
								Instagram
								LinkedIn
							Youtube
								Pinterest
								Snapchat
								Email
			LANGUAGES
				Español
							繁體中文
							Tiếng Việt
							한국어
							Tagalog
							Русский
							العربية
							Kreyòl Ayisyen
							Français
							Polski
							Português
							Italiano
							Deutsch
							日本語
							فارسی
							English


U.S. Department of Health & Human Services
			Accessibility
			External Links
			Privacy
			Policies
			No Fear Act
			FOIA
			Nondiscrimination
			OIG
			Vulnerability Disclosure Policy
			USA.gov


Exit Notification / Disclaimer Policy Close
 Links with this icon  indicate that you are leaving the CDC website. The Centers for Disease Control and Prevention (CDC) cannot attest to the accuracy of a non-federal website.
				Linking to a non-federal website does not constitute an endorsement by CDC or any of its employees of the sponsors or the information and products presented on the website.
				You will be subject to the destination website's privacy policy when you follow the link.
				CDC is not responsible for Section 508 compliance (accessibility) on other federal or private website. Website Disclaimers
 Cancel Continue