Manual independent double checks of certain high-alert medications have been widely promoted in healthcare to help detect potentially harmful errors before they reach patients.^1,2 Many practitioners, including both new and experienced, have very strong beliefs in the effectiveness and utility of independent double checks, helping to explain their proliferation in practice.³ These positive attitudes about independent double checks are associated with practitioners’ worries about their own human errors. Thus, many perceive the primary purpose of independent double checks as a means of sharing the responsibility for safe medication use.³

Despite positive attitudes about their use, manual independent double checks have long been disputed, discounted, and misused in healthcare. While non-compliance with independent double checks does not seem to stem from a negative attitude towards double checking itself,³ the process is time consuming and often associated with practical problems in carrying them out, such as staffing shortages⁴ and disruptions in workflow.^4-6 The inconsistent use and variability in how independent double checks are performed has limited their ability to detect many errors, and their impact on safety has been questioned by those who rarely find mistakes during the checking process. Frequent misuse of an independent double check as a quick fix for an ailing medication use system has often been a perceived solution to many serious errors that have reached the patient. Furthermore, the overuse of manual independent double checks as a risk-reduction strategy for high-alert medications has been called to task given that it is a weaker error-reduction strategy, particularly if this is the only safeguard in place.

Despite these challenges, ISMP believes that the selective and proper use of manual independent double checks can play an important role in medication safety. Numerous studies (Table 1) have demonstrated the ability of independent double checks to detect up to 95% of errors.^7-11 Based on this, an error rate of 10% (1 in 10) can be reduced to 0.5% (1 in 200) by introducing an independent double-check process. Automated double checks such as computerized allergy screening and barcode scanning may yield better results, and practitioners who have experience using these automated technologies may place lower value on the effectiveness of manual independent double checks.³ However, there is enough evidence today to suggest that conducting a manual independent double check is worth the time and effort if this strategy is used judiciously and carried out as follows.

**_{Table 1.}**_{Examples of Studies on the Impact of Double-Check Systems}
Study	Description	Error Rate (ER) or Error Detection Rate (EDR)	Comments
Campbell GM, et al.⁷ 1998	Use of process control charts to monitor dispensing errors and errors detected with an independent double check	EDR: 95%	An independent double check detected 95% of errors, leading to a reduction in the error rate from 5% to 0.25%
Grasha AF, et al.⁸ 2001	Studied errors pharmacists found when they randomly checked completed prescriptions awaiting pick-up	ER per 5,700 prescriptions: 4.2%	Double checks identified 4.2% of errors not detected prior to dispensing; of these, 2.1% were potentially clinically significant
Grasha AF, et al.⁸ 2001	Introduced artificial errors into medication carts and sample pharmacy orders and measured detection rate with an independent double check	EDR: 95%	The ability to detect and correct 95% of errors with an independent double check was not affected by workload or time on shift
Jensen LS, et al.⁹ 2004	Reviewed drug errors detected during anesthesia with second person double check and prevention strategies	EDR: 58%	Second person double check was the single most effective measure in the study
White RE, et al.¹⁰ 2010	Simulation to test ability of second nurse to detect wrong patient errors using checklists with and without prompt to verify patient identifiers	EDR with checklist: No prompt: 15% With prompt: 80%	Use of checklist with prompts when conducting a second nurse double check led to higher (433% increase) detection of wrong patient errors
Douglass AM, et al.¹¹ 2018	Compared single check to double check by emergency department and critical care nurses during an adult sepsis simulation	EDR: Dosing: Single check: 9% Double check: 33% Wrong vial: Single check: 54% Double check: 100%	Use of a double check was significantly more effective than a single check at detecting wrong-vial errors; also more effective but less pronounced for detecting weight-based dosing errors

Conduct Double Checks Independently

To be most effective, the double check must be conducted independently by a second qualified person.^1-11 If the double check is conducted independently, it reduces the risk of confirmation bias that may occur if the same person prepares and checks a medication, as they likely will see only what they expect to see, even if an error has occurred. An independent double check requires two people to separately check the targeted components of the work process, without knowing the results of their colleague. For example, a pharmacist recalculates the prescribed dose of chemotherapy, prepares a syringe of the medication, and compares the product to the order; then, a nurse independently checks the order, recalculates the dose, and compares the results with the dispensed product for verification. Two people working independently are unlikely to make the same mistake. If they work together or influence the checking process by suggesting what the checker should find, both could follow the same path to an error. So, holding up a syringe and a vial and saying, “This is 5 units of insulin, can you check it?” is not effective because the person asking for the double check is influencing the person checking the product. While delayed self-verification of work conducted hours or days after initial completion has proven valuable when an independent double check cannot be accomplished, practitioners are clearly better at detecting the errors of others than their own errors.⁸

Unfortunately, observational studies and surveys have shown that practitioners are discordant on what constitutes a good double check.^3,4 For example, in a 2016 study, only a quarter of practitioners regarded the independence of a double check as an essential feature, whereas three-quarters thought that doing the check together was preferred.⁴ So, it is crucial to clearly explain the concept of independent double checks and the process to be followed.

Use Independent Double Checks Judiciously

With workload issues ever present, independent double checks should only be used for very select high-risk tasks, vulnerable patients, or high-alert medications that most warrant their use. ISMP does NOT recommend the use of an independent double check for all high-alert medications, all vulnerable patients (e.g., pediatrics), or all high-risk tasks. Lack of time to carry out the checking process properly is a strong, recurring theme in studies of failed independent double checks and staff resistance to this strategy.^10,12 Fewer independent double checks strategically placed at the most vulnerable points of the medication use process will be much more effective than an overabundance of independent double checks.

The targeted tasks and medications that require an independent double check should not be based simply on those that have historically been double checked, but rather on a careful assessment of:

Processes and medications (e.g., intravenous [IV]/epidural opioids, IV insulin, IV heparin, IV chemotherapy) that pose the greatest risk of harm if an error occurs
The primary reason for the independent double check (what you are trying to catch) and what specifically needs to be verified to achieve that goal
Whether an independent double check is the best strategy to detect a specific risk or prevent a specific error
How the independent double check fits in with other risk-reduction strategies that might address the same or a similar safety concern

Failure mode and effects analysis (FMEA), hazard and event analysis, and review of the literature and external reports of risk and errors can help inform practitioners about the processes and medications that pose the greatest risk of harm to patients that might be targeted for an independent double check. Also, careful consideration should be given to what you are trying to verify or catch with the independent double check to evaluate whether this would be the best risk-reduction strategy. For example, if the purpose of an independent double check is to verify that the correct drug, dose, and patient have been selected prior to administration, bedside barcode scanning will offer a more reliable verification strategy than a manual independent double check. On the other hand, if the concern is infusion pump programming errors and possible line mix-ups, then an independent double check at the bedside may be the best risk-reduction strategy.

Also be sure to evaluate all the other ways you are currently mitigating the risk apart from the independent double check. For example, when determining whether you will continue to require a nurse to independently recalculate an oncology patient’s body surface area (BSA), you may find that this specific redundancy is already calculated by the prescriber, recalculated in the electronic health record, confirmed by a nurse practitioner, and independently double checked by several pharmacists. However, during this evaluation, you may notice that no one is verifying that the chemotherapy has been prescribed for the correct cycle and day (per protocol), and this would be a more effective place to implement an independent double check, particularly upstream in the pharmacy, than requiring another level of redundancy with calculating the BSA.

When such re-evaluation results in elimination of an independent double check or changes in the frequency or focus of a check already in place in a unit/department, do not be surprised if practitioners are reluctant to give them up. Due to a status quo bias, practitioners often regard the extent of independent double checks on their unit as ‘exactly right’ and may resist giving up an independent double check they have come to rely on, or may have reservations about introducing a new independent double check.⁴ A detailed discussion about other safety nets in place before removal of an independent double check, or a story about the short pathway to a harmful error without the addition of a manual independent double check, could help improve staff acceptance and compliance.

Also, do NOT use independent double checks as a means of fixing problems when more fundamental system redesign is needed. Independent double checks are a poor substitute for system improvements that help prevent errors. Strategies with higher leverage (e.g., use of barriers, computer alerts with hard stops, standardization, barcode scanning) should be considered. Any errors uncovered during the double-check process should also be used for learning and system improvement.

Avoid Sole Reliance on Independent Double Checks

Independent double checks can sometimes fail, especially since the process essentially depends on one fallible person assessing another fallible person’s work. The origin of the error can also predict a certain amount of failure with even the most robust independent double-checking process. An exogenous error arises from conditions in the external environment, such as poor design of drug packages and labels, complex task characteristics, or unclear presentation of information.¹³ Double checks are often less successful in detecting exogenous errors, even when the check is performed independently. Some of the same external factors that initially led to the error are often still present, and people in the same environment could easily make the same mistake during the double check.

On the other hand, an endogenous error arises solely within an individual from a random and unpredictable cognitive event like miscalculating a dose.¹³ Another person performing the same function will rarely make the same exact mistake. Therefore, endogenous errors are likely to be detected if a double check is performed independently.

Conduct a Cognitive Review of the Medication

Analysis of failed independent double-check processes and interviews with staff suggest that double checking often becomes a superficial, routine task, and people may lose sight of its importance.^3-6 These failed checking processes can often be traced to common themes:^4,11,12,14

Auto-processing in which the person checking the work of another does so in a habitual manner with little real appraisal
A failure to look for and process additional information once initial information looks correct (satisficing)
A deference to authority in which one person feels constrained to ask questions, or one person easily dissuades the other who sensed a possible error
Excessive trust in the person whose work is being checked
A diffusion of responsibility and overreliance on double checking in which staff believe someone else will catch any mistakes, leading to a false sense of safety
Distractions and interruptions

What is often missing in the independent double-check process is a “sterile cockpit” environment without extraneous conversation, a firm belief that everyone—even the most trusted and reliable staff member—is fallible, and a more cognitive review of all components of the medication, which requires critical thinking beyond verification of the “5 rights.” Is the drug appropriate for the patient? Does the drug’s indication match the patient’s diagnoses or conditions? Is the dose appropriate for this patient? Is the route of administration proper? These questions and more need to be answered independently by both the initial practitioner preparing, dispensing, or administering the selected medication, and by the second practitioner (independently double checking the work of the first practitioner). See Table 2 for other items to consider when conducting an independent double check.

**_{Table 2.}**_{Independent Double Check (to be used selectively)}
A procedure in which two practitioners independently check each targeted component that requires verification when prescribing, dispensing, or administering a medication, which often includes the following:
Comparison to prescriber’s order:
Is this the right patient? Is this the prescribed drug? Is this the prescribed dose/strength/rate of infusion? Is this the prescribed route of administration? Is this the prescribed frequency/time for drug administration?
Additional cognitive checks:
Does the drug’s indication match the patient’s diagnoses or conditions? Is this the right formulation of the drug? Is the dose appropriate for this patient? Based on the patient’s weight/age/laboratory values? (if appropriate) Is the dosing formula used to derive the dose correct (e.g., mg/kg, mcg/kg/min, mg/kg/hour)? Are dose calculations correct? Has the dose of a liquid medication been measured correctly? Has the right type of syringe/cup been used? Is the dosing frequency/timing appropriate for this patient? Is the route of administration safe and proper for this patient? Is the medication within its expiration date? Does the patient have any allergies or cross allergies to this medication? Have appropriate monitoring tests been ordered? Are the test results upon which a dose has been prescribed, verified as belonging to this patient? For IV push or parenteral infusions (if applicable) Are flush syringes available and labeled?* Is this the correct diluent and volume of diluent? Is the total volume correct? Are pump settings correct? Is the infusion line attached to the correct port and pump/channel? Is the rate of a bolus dose correct?

^{*Flush syringes are intended for flushing lines before/after drug administration, not for reconstitution or dilution of medications.}

Standardize the Process and Provide Tools

Ask a roomful of practitioners from a single unit/department to describe the independent double-check process and you are likely to get a variety of answers. Variations in how independent double checks are carried out abound, and compliance with all the steps in the process is often inconsistent.¹² Some may even view an independent double check as a process that simply requires a second signature or biometric scan before the work can be completed, without really understanding the goal of the check or the steps that should be followed prior to “signing” off on the work. To reduce inconsistencies, establish a standard process for carrying out an independent double check, and educate staff about its importance and how to carry it out properly—as an independent cognitive task and not a superficial routine task or just a “cosigning” requirement.

Make it easy for practitioners to follow and document the independent double-check process without relying on vigilance and memory.¹⁵ One way to do this is to create a checklist (electronic or paper) as a reminder of the components of certain critical processes and/or medications that should be checked (e.g., chemotherapy preparation prior to dispensing). The questions in Table 2 can be used as a broad template to start an intuitive checklist. However, checklists that include very specific items associated with critical information, rather than more general topics, significantly improves their effectiveness.¹⁰ For example, a checklist that instructs users to check the medication label against the original order is not as effective as a checklist that specifies the exact elements to check on the label and the drug order.¹⁰ Nevertheless, design the checklist with care so that the detail does not replace the need for the practitioner to think critically about each aspect of the independent double-check process. Make sure the sequence of information on checklists follows the logical progression of typical workflow and uses the same terminology. The checklist can also serve as a means of documenting the independent double check.

Conclusion

Conduct a thorough evaluation of whether independent double checks are being used judiciously and properly in your facility. After carefully considering what you are trying to verify or catch, the necessary steps to achieve this goal, and if an independent double check is the best strategy, you might determine that it is advantageous to change the focus or the process of the check, or to eliminate it in favor of other more effective risk-reduction strategies. It is also important to determine if certain high-alert medications or vulnerable steps in critical processes currently do not require an independent double check but need one. If so, implement an independent double check as outlined above, then monitor compliance, assess how often the checks are conducted as designed, and make the necessary revisions to promote effectiveness. Staff surveys may also be useful in gathering information about perceptions associated with independent double checks. When employed judiciously, conducted properly, and bundled with other strategies, manual independent double checks can be part of a valuable defense to prevent potentially harmful errors from reaching patients.