What’s the Best Way to Reduce False Positives in Sterility Testing?

In order to release sterile medicines and products to the market, they must first pass a sterility test.


How to help ensure sterility testing is a million-dollar question for every pharmaceutical firm. In this article, we break down which of the four common approaches is the most effective at reducing false positives.

The stakes for sterility testing couldn’t be higher. If medicine is contaminated, and an improperly performed sterility test does not detect it (i.e. a false negative), it could lead to contaminated medicine being released which could cause harm or in severe cases even death of patients. 

In contrast if medicine is not contaminated, but the sterility test becomes contaminated by the operator or environment i.e. a false positive, then the impact of this can delay product release; and at worst, it can lead to millions of dollars lost in scrapped product. 

To reduce false positives, sterility testing should be conducted in an aseptic environment. There are various barrier system configurations used to produce an aseptic environment. The most common approaches are outlined below.

Grade A Cleanroom

Grade A (ISO 5) cleanrooms are effective for conducting sterility tests as they provide a clean environment for protecting batches from pathogens.

But there’s a catch.

The problem with grade A cleanrooms is that people are physically present in the room with no separation between personnel and the sample being tested. As personnel are the biggest source of contamination, this creates a risk of contaminating the sample and generating a false positive. 

The other challenge with this approach is that cleanrooms of this grade are extremely expensive to maintain and space is at a premium. They often use more space and resources than is actually necessary. So this is not a cost effective approach to sterility testing. 

Biological Safety Cabinet or Laminar Airflow Hood in Grade B Cleanroom

A biological safety cabinet (BSC)/ Laminar Airflow Hood (LAF) is a semi enclosed workspace that provides limited environmental protection of pathogens from the sample being tested, through the use of unidirectional airflow. As personnel are the biggest source and risk of contamination, this is a major advantage and means that this approach offers a better level of protection than a grade A cleanroom.

The additional protection of a BSC means that the process can be performed in a lower grade cleanroom therefore, this approach incurs a lower running cost than a grade A cleanroom and generally requires less space. 

However, the limitation of this approach is that BSCs are still technically open to the environment so there is still potential for human exposure onto a sterility testing sample. To get around this constraint, some manufacturers are turning to devices that combine the cost saving benefit of a biosafety cabinet with the effectiveness of cleanrooms. 


An isolator is a workspace that is completely isolated from personnel and the environment, that allows operators to conduct sterility tests while maintaining an aseptic workspace. An isolator is essentially a sealed enclosure which provides HEPA filtered laminar airflow facilitating a grade A environment. Users conduct tests through gloves mounted on the isolator. This degree of separation reduces or eliminates the risk of a sterility test sample being exposed to personnel, so offers the lowest risk approach to sterility testing. Many isolators can also be connected to an external decontamination system and decontaminated with hydrogen peroxide vapor. 

Hydrogen peroxide vapor decontamination provides an alternative to manual disinfection which is prone to human error. The decontamination process provides a 6-log sporicidal kill and ensures an even coverage on all surfaces, meaning that disinfection can be reliably achieved, when used according to the directions for use, on the surfaces of the test materials and equipment loaded into the chamber between each sterility testing batch, which reduces the risk of contamination substantially.

Isolators have become popular because they combine the cleanliness of a cleanroom but with a smaller profile. In fact, Section XI of the FDA’s 2004 guidance states, “The use of isolators for sterility testing minimizes the chance of a false positive test result.”

Despite the benefits, traditional isolator systems can be unwieldy. 

The most common isolators are large boxes built from stainless steel. Their large size, heavy weight and specialized parts make them a permanent fixture of the room they are installed in. This translates into longer lead times when purchasing a new isolator system. Traditional isolator systems can take 10-12 months to manufacture, deliver, install and validate; and any large equipment built from stainless steel tends to be fairly expensive.

Isolator systems are also often situated in a grade B cleanroom, which compounds, rather than solves, the problem of cost-effectiveness. However, as isolator systems provide full separation between the environment, isolator systems can be located in lower grade cleanrooms which cost less to maintain.

Cleaning isolators can also be a challenge, since they have a large internal surface area and rarely have a built-in decontamination system. This makes decontamination between each batch of testing time-consuming.

So while traditional isolator systems offer many benefits, there are factors which make them difficult to implement. Because of this, many manufacturers are starting to use a newer, more efficient and cost-effective approach. 

Modular Isolator System with Integrated Bio-Decontamination

Much like traditional isolator systems, this approach utilizes hydrogen peroxide vapor to decontaminate loads before performing a test, but the key difference is that the vapor generator is fully integrated into the isolator; rather than being separate. 

With built-in rapid bio-decontamination capability, an isolator with an integrated bio-decontamination generator requires a smaller footprint than a traditional isolator system, typically has a lower energy consumption and is often more cost effective as the isolator system and bio-decontamination generator do not have to be purchased separately.

Compared to a traditional isolator system, the added benefit of a modular isolator system is that the testing output is increased substantially as a sterility test can be performed in one chamber whilst the next load is being decontaminated in the adjacent chamber at the same time.

Some modern modular, isolators systems with an integrated bio-decontamination generator are typically smaller than traditional isolator systems and are made of polypropylene. This makes them lighter, easier to assemble and more cost-effective and means that manufacture, install, and validation can be performed in a much shorter time span of 3-4 months compared to a traditional isolator system.

With other features such as environmental monitoring, and an integrated sterility testing pump, it’s this combination of benefits – isolation, cost-effectiveness, flexibility, size – that has led to many leading pharmaceutical companies to adopt modular isolator systems with integrated bio-decontamination in their facilities, for sterility testing.

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