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The Delaware Public Health Laboratory follows the reverse syphilis serology testing algorithm recommended by CDC and the Association of Public Health Laboratories (APHL). This algorithm involves a combination of highly sensitive but somewhat non-specific rapid screening tests and highly sensitive and specific confirmatory tests for syphilis. All tests in the algorithm can be performed on one single sample of patient serum.


  • Serologic Test for Syphilis
    • Syphilis TP Chemiluminescent microparticle immunoassay (TP-CMIA)
    • Rapid Plasma Reagin (RPR)
    • Venereal Disease Research Laboratory (VDRL)
    • Treponema Pallidum-Particle Agglutination (TP-PA)


  1. Obtain 5-10 ml of blood from the patient using standard venipuncture technique. Collect the blood into an anticoagulant free (i.e. "clot") tube or serum separator tube (SST). Plasma (purple top tube) may be used up to 48 hrs. from collection.
  2. Label tube with patient’s full name, date, and time of collection.
  3. Complete the Test Requisition Form or order request online through our Laboratory Information Management System (LIMS). Specimen and forms should be placed in a designated location at each site for the lab courier to pick up.
  4. Allow specimen to clot and label with a unique identifier to match requisition form. Wherever a centrifuge is available, specimens should be spun on the same day of collection. Arrange for transport to laboratory. If transportation is delayed, refrigerate tube to minimize hemolysis.


SEROLOGIC TESTS FOR SYPHILIS (STS): Two types of antibodies are measured by these tests:

  • DPHL offers nonspecific "non-treponemal" antibody screening tests, including the rapid plasma (RPR) and Venereal disease research laboratory test (VDRL). These reaginic antibodies, while almost always produced by patients with syphilis, may also be produced by patients with other infectious diseases, autoimmune disorders, pregnancy, old age, and recent immunization.
    • Positive tests should be confirmed by specific antibody test, see below.
  • DPHL offers a specific "treponemal" antibody assay, called the Trepenema pallidum particle agglutination (TP-PA) test. This assay is used to confirm positive TP and/or RPR test results, or upon request by submitting facility.


Expected turnaround time is 1-3 workdays for both negative and positive reports. Initial TP and/or RPR positive results are confirmed with TP-PA testing according to the reverse syphilis serology testing algorithm. Patients that have been previously confirmed positive do not warrant repeat confirmatory testing.

Negative screening tests are not routinely confirmed unless certain and rare extenuating circumstances, such as untreated tertiary syphilis, are present. Contact the laboratory if it is suspected that the patient falls into this category.

FTAs are sent to a reference lab and require 2-3 weeks.


Samples will be rejected if they are:

  • Unlabeled - All specimens MUST be appropriately labeled.
  • Insufficient in Quantity - No specimen received, no specimen in container, or less than 1.0 mL of blood received.
  • Hemolyzed - Specimens must be free of hemolysis.
  • Damaged - Specimen leaked or broken transit.
  • Too Old - Samples greater than 5 days old are unreliable specimens for testing.

Return to Laboratory Specimen Collection Procedures page.

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This page was last updated 3/24

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