Cause Analysis: The 5 whys method

June 15, 2023

Although CLIA includes brief requirements for corrective actions, it does not include a requirement for cause analysis (also referred to root cause analysis). However, a core element of the ISO management system requirements that form the basis for ISO 15189 is corrective action, starting with cause analysis. The standard is designed to place planned, thoughtful consideration and investigation into how the nonconformance occurred and dig deeper into the issue and determine how to prevent future recurrence. In addition, a cause analysis can also prevent deficiencies that have yet to occur. Oftentimes, a single issue can be the cause of multiple nonconformities, and therefore, solving one issue will reduce the risk of another occurring.

Properly identifying the problem through cause analysis is critical not only to achieve and maintain ISO 15189 accreditation, but also to maintain high-quality patient care.

A top-down approach

Cause analysis takes a top-down approach by first identifying the deficiency then taking small steps to dig deeper and determine the root of the nonconformity. One of the best ways to do this is using a method called “the 5 Whys.” As the name suggests, the process involves identifying a problem statement and asking yourself “why” a multitude of times until the cause can be identified. The answer to each question should parrot the problem statement before it for logical transitions and a clear line of thought.

Take, for example, internal quality control materials failed to fall within the defined range of acceptability. ISO 15189 requires labs to ensure the validity of examination results in clause, stating, “When internal QC defined acceptability criteria are not fulfilled and indicate results are likely to contain clinically significant errors, the results shall be rejected and relevant patient samples re-examined after the error has been corrected.”

In this case, the problem statement would read, “The internal quality control materials failed to fall within the defined range of acceptability, causing a rejection of results and the need for another test to be performed. Now, it’s time to start asking ‘why?’.

Why 1: Why did the quality control materials fail to fall within the acceptable range?

Answer 1: The quality control materials failed to fall within the acceptable range because the test was performed incorrectly by the technician.

Why 2: Why did the technician perform the test incorrectly?

Answer 2: The technician performed the test incorrectly because they missed a crucial step in the method.

Why 3: Why did the technician miss a step in the test method?

Answer 3: The technician missed a step because they weren’t provided the proper training on the test method.

Why 4: Why did the technician not receive proper training on the test method?

Answer 4: The technician did not receive proper training on the test method because it was not documented in the training documents.

Why 5: Why was this test method not documented in the training documents?

Answer 5: The test method was not documented in the training documents because it was added to the scope of accreditation before the scheduled review of training documents.

Resolution: When adding new methods to the scope of accreditation, document an additional step to incorporate the method into the training documents.


While basic, this is a common example of how deficiencies can happen in the laboratory and how to properly determine the core of the issue. Depending on the complexity of the nonconformity, you may only need to ask “why” three or four times before finding the cause. In other cases, you may need to ask “why” seven or eight times before you reach the true cause. Once the source of the problem and the resolution are properly determined, the corrective action can take place.

The answers to your questions may not always be obvious, so take the necessary time to thoroughly investigate. A comprehensive cause analysis will inevitably save you time in the future that may have been spent resolving related issues. It will also reduce risk in the laboratory and ensure that patients and their doctors continue to receive high-quality laboratory results that they can use to confidently make medical decisions.