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Not medical advice. This page gives general product and regulatory information for lab, clinic and supply staff. It is not clinical guidance and it does not replace the manufacturer’s instructions for use.
Short answer
Ortho-phthalaldehyde (OPA) is a high-level disinfectant used on heat-sensitive medical instruments such as endoscopes. The CDC states that the product received FDA clearance in October 1999 and contains 0.55% 1,2-benzenedicarboxaldehyde. It is not a sterilant: 0.5% OPA was not sporicidal after 270 minutes of exposure. The same name also refers to a reagent used in amino acid analysis, covered below.
Definition and scope: one name, two jobs
The term covers two unrelated uses, and searchers often land on the wrong one.
| Meaning | What it is | Where to go on CASRAI |
|---|---|---|
| High-level disinfectant | A 0.55% solution for reprocessing heat-sensitive instruments, described in the CDC disinfection guideline | This page, plus high-level disinfection and the Spaulding classification |
| Analytical reagent | A derivatization reagent used with a thiol to make primary amines detectable in amino acid analysis by HPLC | amino acid analysis derivatization methods |
The rest of this page covers the disinfectant. Per the CDC, OPA solution is a clear, pale-blue liquid with a pH of 7.5.
How it is used in practice
The CDC lists OPA among the chemical high-level disinfectants for semicritical instruments. NIOSH, which evaluated eight healthcare facilities, found most exposed participants used OPA in basins or containers rather than automated machines, and about half used it every day. The same report notes that facilities checked concentration with test strips for minimum effective concentration and reused the solution for several days, with a manufacturer recommendation to change it out at 14 days or less, as stated in that report for the facilities’ product.
Exposure steps NIOSH identified were diluting or pouring, opening the container, removing instruments, rinsing, disposal to the sewer, and maintenance of automated processors. For where this step sits in the wider workflow, see endoscope reprocessing.
One label, different contact times
The CDC explains that high-level disinfectant label claims for OPA at 20 C vary worldwide because of differences in test methodology and requirements for licensure. Activity is also directly related to temperature.
| Setting (CDC guideline) | Label contact time |
|---|---|
| United States | 12 minutes |
| Canada and Australia | 10 minutes |
| Europe, Asia and Latin America | 5 minutes |
| Automated endoscope reprocessor with FDA-cleared capability to hold 25 C | 5 minutes |
The practical reading is that a number quoted from another country or a study is not the number for your product. Use the label and instructions for use of the product you actually hold.
Related concepts: OPA compared with glutaraldehyde
OPA was introduced to the US market in 1999 as a safer alternative to glutaraldehyde, according to NIOSH. Every row below comes from the CDC chemical disinfectants page (checked 2026-10-30).
| Feature | What the CDC says |
|---|---|
| Stability | Excellent stability over a pH range of 3 to 9 |
| Eyes and nasal passages | Not a known irritant |
| Odor and activation | Barely perceptible odor; requires no activation |
| Exposure monitoring | Does not require exposure monitoring (see the NIOSH point below) |
| Spores | 0.5% OPA was not sporicidal with 270 minutes of exposure |
| Staining | Stains proteins gray, including unprotected skin |
For other chemistries see types of disinfectants and peracetic acid.
Where it matters for labs, clinics and supply decisions
- Residue and staining. The CDC notes that residue on inadequately rinsed transesophageal echocardiography probes can stain a patient’s mouth, so thorough rinsing is part of the disinfectant’s use, not an optional extra.
- Urologic instruments. Of approximately 1 million urologic procedures with OPA-reprocessed instruments, the CDC reports 24 cases of anaphylaxis-like reactions after repeated cystoscopy, typically after four to nine treatments. The CDC states the manufacturer recommends thorough rinsing and not using OPA on urologic instruments used for patients with a history of bladder cancer.
- Workplace exposure. NIOSH reported that neither NIOSH nor OSHA has established an occupational exposure limit for OPA. Geometric mean personal breathing-zone concentration was 0.34 μg/m³ for exposed participants versus 0.14 μg/m³ for comparison participants, and the two highest readings were 35 and 38 μg/m³. Five participants had positive allergy skin tests to OPA; skin sensitization was not confirmed, and no participants had skin staining.
- Training content. NIOSH found that one facility’s training material stated OPA was not a potential workplace problem because there is no OSHA permissible exposure limit. Its report states that the lack of a limit does not imply that a potential health hazard does not exist, and recommends at least annual refresher training, PPE and ventilation.
- Disposal. The CDC says disposal follows local and state regulations.
Common misunderstandings
- “High-level disinfectant means sterilant.” No. The CDC reports 0.5% OPA was not sporicidal at 270 minutes.
- “No exposure limit means no hazard.” NIOSH addressed this directly, as above.
- “The contact time is the same everywhere.” It is not; see the table above.
- “It is the same as the OPA used in HPLC.” The reagent and the disinfectant share a name, not a use.
FAQ
What is ortho-phthalaldehyde used for?
As a disinfectant it is used for high-level disinfection of heat-sensitive medical instruments; as a reagent it is used for derivatizing primary amines in amino acid analysis.
Is OPA a sterilant?
No. The CDC reports 0.5% OPA was not sporicidal with 270 minutes of exposure.
How long does OPA need to act?
It depends on the label and temperature. The CDC lists 12 minutes in the US, 10 in Canada and Australia, 5 in Europe, Asia and Latin America, and 5 minutes in an automated reprocessor that holds 25 C. Follow the product’s instructions for use.
Does OPA have an occupational exposure limit?
NIOSH reported that neither NIOSH nor OSHA has established one.
Sources
- CDC, Chemical Disinfectants, Guideline for Disinfection and Sterilization in Healthcare Facilities, https://www.cdc.gov/infection-control/hcp/disinfection-sterilization/chemical-disinfectants.html, checked 2026-10-30.
- NIOSH, Health Hazard Evaluation Report 2006-0238-3239, Evaluation of Ortho-phthalaldehyde in Eight Healthcare Facilities, https://www.cdc.gov/niosh/hhe/reports/pdfs/2006-0238-3239.pdf, checked 2026-10-30.
