Root Cause Analysis In Coagulation Testing

by Donna Castellone, MS, MT (ASCP) SH • July 14, 2022

The interpretations below are provided by Donna Castellone, MS, MT (ASCP) SH for Aniara Diagnostica.

On thing for sure, coagulation testing is complex. When there is an issue, it is hard to distinguish if it is due to the patient, sample, reagent or the test itself? Adding in preanalytical variables can really compound a problem. So what is the best way to solve problems? You can't just say reagent instability or poor sample unless you are absolutely sure that is the problem. Sometimes conducting a root cause analysis will help you get to the heart of the problem.

Errors can lead to undue repetition of laboratory tests, more invasive testing and consultations that create discomfort and increased costs for patients and the healthcare system. Most errors are due to pre-analytical factors (46-68.2% of total errors), High error rate (18.5-47% of total errors) has also been found in the post-analytical phase. Errors due to analytical problems have been significantly reduced over time.1

A root cause analysis can be used to target system wide improvement by identifying causes that are within the laboratories control to remedy. Usually caused by bad processes 80% caused by systems 20% caused by acquired behaviors. The possible causes include physical causes. These are tangible, material items failed in some way (analyzer stopped working). Human causes meaning that someone did something wrong or did not do something that was needed. Human causes typically lead to physical causes (analyzer broke because no one emptied the waste). Organizational causes would include a system, process, or policy that people use to make decisions or do their work is faulty (no record of when waste was changed).2


Let's conduct a root cause analysis by looking at a failure of a questionable factor assay result:


A factor VIII assay was received in the laboratory and the result was <1% however the aPTT for that patient was within the normal range of 35.1 (28-37 seconds). Is this correct? Should this be reported out? How do you handle this? A good beginning is to conduct a root cause analysis and as Why at least 5 times.

Three common mistakes made when approaching Problem Solving (based on assumptions) is assuming you know what the problem is - without studying it or asking enough questions; assuming you know how to fix the problem – without knowing what the problem really is and assuming you know what the true cause of the problem is – without confirming it. It is important to identify the problem, collect data, identify possible causal factors- ask why, why, why, why, and why. This will aid in identifying the root cause at which point you can then recommend and implement solutions.

Where do you begin?

WHY did we get this result?

  1. Look at the sample- is the sample clotted? Are their small clots in the sample? What is the ratio of blood to anticoagulant, overfilled underfilled?

Pre-analytical variables can greatly impact the quality and accuracy of coagulation results. It is important to be able to identify these variables. Having poor standardization of operating procedures can result in different practices within the same laboratory. This can contribute to analyzing specimens with poor quality resulting in spurious test results.3 Upon careful investigation, there were no issues with pre-analytical variables. The sample was a fresh draw from the clinic and within stability for a FVIII. It was processed and run in a timely manner.

Why was the aPTT normal with a very abnormal FVIII assay?

The quality control for both the aPTT and FVIII for that day were within the established ranges. The standard curve for the FVIII was also reviewed and was prepared that day and within all established acceptable parameters. This helped to confirm that the aPTT reagent was not in question and the reagent was stable and properly handled and reconstituted.

WHY was the FVIII so low?

Based on the factor VIII sensitivity for this lot of reagents, an aPTT of 36 seconds should yield a FVIII activity of about 66%, which is within the normal range of 50-150%.

WHY was the FVIII affected?

We have already concluded that the aPTT reagent was working correctly based on the results of the aPTT and the controls for all the tests as well as all of the other aPTT based factor assays that were performed. However, there are other reagents involved in performing a FVIII assay including buffer and FVIII deficient plasma. The only reagent specific for FVIII was the deficient plasma which is reconstituted and stable for 4 hours.

Why should the FVIII deficient plasma be in question?

Since there were no issues with any other factors that were performed that day, we can conclude that the buffer is okay. The next thing to investigate is the FVIII deficient plasma. Since it is reconstituted, there may be an issue with it being done wrong, however the quality control was performed at the beginning of the shift was within the established ranges. The next question is the stability of the deficient plasma which is four hours, this is monitored by the analyzer. When investigated, it was noted that the plasma was very close to the end of the four hours were testing was performed. There was sufficient reagents to re-run the QC, and both parameters were out of range.


A fresh vial of FVIII deficient plasma was reconstituted, QC was repeated and the patient sample was re-run. The FVIII activity level was 70% and the aPTT repeated at 35 seconds which aligned with expected values.

How does this help?

Many issues are handled by technologists automatically re-running results or re-running the standard curve without sequentially looking at possible reasons for errors. This root cause analysis also uncovered that the factor deficient reagent in our testing environment was not stable for 4 hours and caused an investigation into the stability of the deficient plasma. It also helped the technologist to be critically aware of the stability of the FVIII and its impact on FVIII levels.


Using a step-by-step approach to solve coagulation problems is part to a good quality management system. It can also uncover other issues including best practices used by technologists, equipment or reagent issues. Getting to the root cause of a problem can help to ensure that it is truly solved and may prevent it from happening in the future. All of these measures can ensure optimal and safe results for your patients.


  2. Collazo, G., Controlling human Error, 8/8/17 Compliance 4all
  3. Marcel du Toit 1, Zivanai C Chapanduka 1, Annalise E Zemlin 2, The impact of laboratory staff training workshops on coagulation specimen rejection rates, 2022 Jun 3;17(6):e0268764. doi: 10.1371/journal.pone.0268764. eCollection 2022.