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What’s New in the Patient Safety World

February 2022

Does Time of Day Matter?



We’ve done multiple columns on “the weekend effect” and “the after hours effect”, in which patient outcomes tend to be worse than for those during “normal” daytime hours. But beyond time of day or day of the week, there is variation in performance by time during a working shift.


In our May 3, 2011 Patient Safety Tip of the Week “It’s All in the Timing” we noted that detection rates for polyps or adenomas during colonoscopy fell off during colonoscopies done later in a shift. And in our June 2019 What's New in the Patient Safety World column “More on the Time of Day” we noted your chance of getting an influenza vaccination or one of several preventive screening procedures also falls off when you are seen late in the day.


The phenomenon is seen in radiologists, too. In our August 25, 2020 Patient Safety Tip of the Week “The Off-Hours Effect in Radiology” we noted a study which looked at the performance of radiology fellows who have completed full radiology residencies (all of whom successfully completed the American Board of Radiology board certification following their fellowship year), comparing CT scan reading error rates during daytime or night shifts (Patel 2020). Nighttime studies had error rates of 3%, compared to 2% for daytime studies, and 69% of the radiology fellows had higher error rates for night cases. But, while the focus of the study was on nighttime vs. daytime error rates, there were significantly more errors during the last half of night assignments (3.7%) compared with the first half (2.5%). Diagnostic error rates were also lower in the first half of the day assignment from 7:00 AM to 11:59 AM compared with the second half from 12:00 PM to 5:59 PM (1.1% vs. 2.6%), but that difference was not statistically significant.


A new study (Bernstein 2022) showed that patients were more likely to be recalled when their screening digital breast tomosynthesis images were interpreted later in the day by less-experienced radiologists. Thr researchers looked at recall and false-positive (FP) rates in radiologists’ interpretation of digital breast tomosynthesis (DBT) images digital mammography (DM) images (the authors note that digital breast tomosynthesis image interpretation might be more cognitively demanding than interpretation of digital mammography images). But they also looked at the impact of time of day on these rates.


Overall, for every additional hour of reading time, the odds of recall increased by 6.6% for DBT, a sharper increase than that for DM. Similarly, for every additional hour in reading time, the odds of an falso positive finding increased by 6.8%, whereas the increase for DM was 3.9%. For every additional hour in reading time, the odds of a true positive finding increased by 3.4% for DBT and by 2.2% for DM. But results were significantly impacted by experience of the radiologist. For radiologists with 5 or fewer posttraining years of experience, odds of recall increased 11.5% with every hour when using DBT, but this was not found for DM. For radiologists with more than 5 posttraining years of experience, no evidence of increase in recall was observed for DBT or DM.


Physicians, nurses, and really all healthcare workers tend to have drop-offs in performance when fatigued. There are, of course, multiple studies demonstrating the impact of fatigue on on radiologists. Krupinski et al. (Krupinski 2010) found that, after a day of clinical reading, radiologists have reduced ability to focus, increased symptoms of fatigue and oculomotor strain, and reduced ability to detect fractures. In our April 2018 What's New in the Patient Safety World column “Radiologists Get Fatigued, Too” we highlighted a study looking at the effect of overnight shifts on performance of radiologists (Hanna 2018). The researchers used a tool for measuring fatigue and advance eye tracking technology to assess the performance of radiologists (both attendings and residents). Not surprisingly, participants demonstrated worse diagnostic performance in the fatigued versus not-fatigued state. Viewing time per case was significantly prolonged when the radiologists were fatigued. Mean total fixations generated during the search increased by 60% during fatigued sessions. Mean time to first fixate on bone fractures increased by 34% during fatigued sessions. Moreover, dwell times associated with true- and false-positive decisions increased, whereas those with false negatives decreased. Effects of fatigue were more pronounced in residents, in keeping with the findings of Bernstein et al. regarding the impact of experience.


Hanna et al. concluded that further research is needed to address and reverse the impact of such fatigue-related changes. They speculate that environmental changes (eg. lighting) and activity changes (eg. periodic breaks, moving around, etc.) might help mitigate the adverse effects of fatigue on performance.



Some of our other columns on the impact of time of day on patient outcomes:


May 3, 2011 “It’s All in the Timing”

June 2019 “More on the Time of Day”

August 25, 2020 “The Off-Hours Effect in Radiology”



Some of our other columns on the role of fatigue in Patient Safety:


November 9, 2010      “12-Hour Nursing Shifts and Patient Safety”

April 26, 2011             “Sleeping Air Traffic Controllers: What About Healthcare?”

February 2011             “Update on 12-hour Nursing Shifts”

September 2011          “Shiftwork and Patient Safety

November 2011          “Restricted Housestaff Work Hours and Patient Handoffs”

January 2012               “Joint Commission Sentinel Event Alert: Healthcare Worker Fatigue and Patient Safety

January 3, 2012           “Unintended Consequences of Restricted Housestaff Hours”

June 2012                    “June 2012 Surgeon Fatigue”

November 2012          “The Mid-Day Nap”

November 13, 2012    “The 12-Hour Nursing Shift: More Downsides”

July 29, 2014              “The 12-Hour Nursing Shift: Debate Continues”

October 2014              “Another Rap on the 12-Hour Nursing Shift”

December 2, 2014       “ANA Position Statement on Nurse Fatigue”

August 2015               “Surgical Resident Duty Reform and Postoperative Outcomes”

September 2015          “Surgery Previous Night Does Not Impact Attending Surgeon Next Day”

September 29, 2015    “More on the 12-Hour Nursing Shift”

September 6, 2016      “Napping Debate Rekindled”

April 18, 2017             “Alarm Response and Nurse Shift Duration”

July 11, 2017              “The 12-Hour Shift Takes More Hits”

February 13, 2018       “Interruptions in the ED”

April 2018                   “Radiologists Get Fatigued, Too”

August 2018               “Burnout and Medical Errors”

September 4, 2018      “The 12-Hour Nursing Shift: Another Nail in the Coffin”

August 2020               “New Twist on Resident Work Hours and Patient Safety”

August 25, 2020         “The Off-Hours Effect in Radiology”

September 2020          “Daylight Savings Time Impacts Patient Safety?”

January 19, 2021         “Technology to Identify Fatigue?”

October 12, 2021        “FDA Approval of Concussion Tool – Why Not a Fatigue Detection Tool?”






Patel AG, Pizzitola VJ, Johnson CD, et al. Radiologists Make More Errors Interpreting Off-Hours Body CT Studies during Overnight Assignments as Compared with Daytime Assignments. Radiology 2020; 297(2): 374-379 Published Online: Aug 18 2020



Bernstein MH, Baird GL, Lourenco AP. Digital Breast Tomosynthesis and Digital Mammography Recall and False-Positive Rates by Time of Day and Reader Experience

Radiology 2022; Publlished online January 11, 2022



Krupinski EA, Berbaum KS, Caldwell RT, Schartz KM, Kim J. Long radiology workdays reduce detection and accommodation accuracy. JAm Coll Radiol 2010; 7(9): 698-704



Hanna TN, Zygmont ME, Peterson R, et al. The effects of fatigue from overnight

shifts on radiology search patterns and diagnostic performance. J Am Coll Radiol 2018; 15(12): 1709-1716








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