The CTAD Tube Dilemma

A comparison of Sodium Citrate/Trisodium Citrate tubes Versus CTAD

In today’s laboratory, we strive to take as little blood from a patient as possible – especially inpatients – while also trying to decrease our costs. So, when our laboratory began performing Anti-factor Xa testing on our Stago Compacts, I was excited because it would allow us to provide better monitoring for our patients on heparin therapy. I was also concerned because in our current Sodium Citrate tubes the stability time is only 1 hour from collection to running, unless you remove the plasma, which will allow stability for 2 hours.

I then set out on a mission to find a different tube that would better fit our needs. Upon researching this, I discovered the CTAD (citrate, theophylline, adenosine, and dipyridamole) tubes. The CTAD tube would give us a 4 hour stability time on the Anti-factor Xa test. But could it be used for our other coagulation testing, such as Protimes, APTT, Fibrinogen and D Dimer?

I found that the CTAD tubes had been verified for use by the BD Vacutainer Corporation for the following tests: PT, INR, APTT, Anti-factor Xa and Platelet factor 4 testing; and they are highly recommended for the Anti-factor Xa test because the CTAD tubes are specially designed to prevent heparin inactivation. The Stago package insert and the BD Manufacturer did not mention use of the CTAD tubes for testing of Fibrinogen and D Dimer. Not wanting to collect 2 different tubes for coagulation testing, I began to formulate a possible solution – thus began my lab study.

I researched not only the BD Manufacturer and Stago package inserts, but I also researched information online and the CLSI document H21-A. According to the Stago reagent package inserts, APTT may be collected in 3.2 percent Trisodium Citrate or preferably CTAD tubes; Anti-Factor Xa may be collected in 3.2 percent Trisodium Citrate (1hour stability) or preferably CTAD tubes (4hour stability). Our Stago representatives also stated the CTAD may also be used for  PT/INR testing. According to the evaluation done by BD Vacutainer, the CTAD tube is acceptable for the following testing: PT, APTT, Anti-factor Xa.

The CLSI document H21-A Anticoagulant states, “Use of 109mmol/L buffered citrate containing theophylline, adenosine, and dipyridamole (CTAD), which may minimize platelet activation, is also acceptable” (pg. 7).  There was no mention of Fibrinogen or D Dimer testing. The document goes on to say, “These anticoagulants (CTAD) are also acceptable for the collection of plasma for coagulation-based assays, and the assays for which they are applicable should be determined from the package insert. If these special anticoagulants are used for routine assays, a normal range specific for that tube matrix should be determined. CLSI documentGP34-A states if an end user chooses to use products for applications other than those claimed by the manufacturer, the user must validate the product for that use. For trueness the samples should be obtained though out the analytical measurement range, samples should also be randomized and collected over different days. A linear regression analysis is to be applied and the slope and intercept should have a 95% confidence interval” (pg. 28).

With this information in mind, it was then agreed that an internal study would need to be completed to determine if we could use a CTAD tube for Fibrinogen and D Dimer. First, let’s perform a comparison of the two tubes:

  • The Sodium Citrate/Trisodium Citrate tubes contain a buffered sodium citrate equivalent to 3.2 percent sodium citrate or 0.109M.
  • The CTAD tubes contain a buffered sodium citrate equivalent to 3.2 percent sodium citrate or 0.109M and theophylline adenosine dipyridamole solution.

According to the manufactures of the CTAD tubes, it is a better tube for Anti-factor XA assays because it inactivates the Platelet Factor IV, which can affect the test. Thus, a clinical study was performed using our current tube (NaCi), containing a 3.2 percent Sodium Citrate solution, and the CTAD tube, containing 3.2 percent sodium citrate and theophylline adenosine dipyridamole solution, to determine if a CTAD tube could be used to meet our coagulation testing needs.

In order to keep with the CLSI document recommendations, the study was collected in the following manner. Thirty-one random patients were selected for collection. The patient pool included outpatients who reflected normal range Fibrinogens and D Dimers, as well as inpatients and nursing home patients who, due to their care and treatment, should have Fibrinogens and D Dimers outside of the normal range. Samples were collected over 6 different days.

Samples were randomized during collection, alternating the order of draw between the NaCi tube and the CTAD tube. Specimens were also randomized upon loading and testing on the Stago analyzers. Samples were spun and tested as soon as possible after collection and then held and retested anywhere from 2-8 hours after collection. The holding and retesting of the samples was performed to check the stability of the tubes for the Fibrinogens and D Dimers.

Upon review of the data, sample stability between the testing intervals was found to be acceptable in both the NaCi and the CTAD. Correlation data between the tubes for the fresh run <2-3 hours from collection and aged run 2-8 hours from collection also fell well within the CLSI guideline limits of >95 percent for the slope and intercept. (See graph appendix)

With these findings and with final approval of our pathologist, we began collecting our Anti-factor Xa tests in the CTAD tubes. If there are additional coagulation tests ordered, then these are also performed from the same CTAD tube as the Anti-factor Xa. The process was worth the work and allowed us to take a minimum amount of blood from the patient and to decrease costs while still caring for our patients.

Graph Appendix:







  1. Clinical and Laboratory Standards Institute. Collection, Transport, and Processing of Blood Specimens for Testing Plasma-Based Coagulation Assays and Molecular Hemostasis Assays: Approved Guideline- (H21-A5) Vol.28 No.5. 2008
  2. Clinical and Laboratory Standards Institute. Validation and Verification of Tubes for Venous and Capillary Blood Specimen Collection: Approved Guideline (GP34-A).
  3. BD Vacutainer® Brand Tube with Sodium Citrate Buffer Solution. Material Safety Data Sheet 2005.
  4. BD Vacutainer® Brand Tube with CTAD Solution. Material Safety Data Sheet 2005.
  5. STA® PTT-A?, Determination of Activated Partial Thromboplastin Time (APTT) Package insert for use in APTT determinations. 24528 – Revised June 2012.
  6. STA®-Fibrinogen, Quantitative Determination of Fibrinogen by STA® Analyzers. Package insert English 3 – Revised August 2012. (.December 1997.)
  7. STA® – Neoplastine® CI? (Cat. # 0605) or STA® – Neoplastine® CI? (Cat. # 0666), or STA-Neoplastine CI PLUS?, (Cat # 00606 )& STA-Neoplastine CI PLUS? (Cat. # 0667), are used for Prothrombin times Determination of Prothrombin Time (PT) by STAÒ Analyzers. Package insert for use in PT determinations. Revised June 2012.
  8. STA® Liatest® D-Di, Immuno-Turbidimetric Assay of D-Dimer by STA® Analyzers. Package insert #23296 ABC – revised September 1997.
  9. STA® – Liquid Anti-Xa (Cat. No. 00311US or Cat. No. 00322US) Colorimetric Assay of Heparins (UFH and LMWH) by STA® Analyzers. Package insert 25536 01 – January 2012.
  10. Yokota M, Tatsumi N, Tsuda I, Nichioka T, and Takubo T. CTAD as a universal anticoagulant. Journal of Automated Methods & Management in Chemistry. Vol. 25, No1 pp17-20 January-February 2003.
  11. BD Vacutainer Systems® Preanalytical Solutions. Evaluation of BD Vacutainer® 2.7 Glass CTAD (Sodium Citrate, Theophylline, Adenosine, and Dipytidamole) Coagulation Tube with Normal Donors, Donors on Oral Anticoagulant Therapy and I.V. Anticoagulant. 2001.

About The Author