Lessons Learned

Waking up on the wrong side of the operating table
Frequency of laterality errors and how to prevent them

August 2013

Laterality errors, also known as side discrepancies, refer to instances when the incorrect side is noted in one or more sections of diagnostic reports or documentation. For example, a radiology report that notes that a lesion is on the left side of the body, when in reality it is on the right, would be considered a laterality error. Uncorrected laterality errors are most frequently associated with wrong-side surgeries, which can result in wrong limb amputation, wrong-side arthroscopy, or resection of wrong-side organ.

A recent study published by several members of the Department of Radiology at Massachusetts General Hospital aimed to determine the frequency of laterality errors in radiology reports using a radiology reports search engine. They found that in the year 2007, 88 side discrepancies were reported in addenda, meaning that the error was put in the report, but was later corrected. However, far more reports are not corrected. In January alone of that year, 36 reports with laterality errors were never corrected (only 7 were corrected that month). Fortunately, only 3 patients were affected and no patient harm occurred.(1)

These errors are not exclusive to radiology. A study published in EYE (journal of the Royal College of Ophthalmologists) found that of the 100 randomly chosen ophthalmology notes, 32 had at least one laterality error (confusing right and left eyes), which equates to incorrect laterality documentation in one-third of the random charts reviewed.(2)

Recommendations on prevention of laterality errors

  1. Avoid using the abbreviations for left and right (L and R). When in a hurry, they are often mixed up and illegible.
  2. Involvement of the patient and/or relatives is very important. When consenting patients for surgery or prescribing treatments, explaining to the patient what is to be done and listening to any queries remains an important mechanism in reducing laterality errors.(3)
  3. Always rely on written information when composing reports or implementing patient care – listening to a staff member orally explain without anything written to back it up can result in errors.
  4. Follow your organization’s procedure for site identification and marking prior to any procedure.
  5. Complete the appropriate “Time Out” steps before a procedure is to be performed.
  6. Do not use the following abbreviations, which have been categorized as “error prone” by the Institute for Safe Medication Practices. Write the words to identify the anatomy involved.

Laterality Error Inducing Abbreviations as noted by the Institute for Safe Medication Practices (ISMP)


auris dextra

right ear

“a” can be mistaken as an “o” which could read “o.d.”, meaning right eye


auris laeva,
auris sinistra

left ear

“a” can be mistaken as an “o” which could read “o.s.” or “o.l”, meaning left eye


auris utraque

both ears

“a” can be mistaken as an “o” which could read “o.u.”, meaning both eyes


oculus dexter

right eye

“o” can be mistaken as an “a” which could read “a.d.”, meaning right ear, confusion with omne in die


oculus sinister

left eye

“o” can be mistaken as an “a” which could read “a.s.”, meaning left ear


oculus uterque

both eyes

“o” can be mistaken as an “a” which could read “a.u.”, meaning both ears


  1. Sangwaiya MJ, et al. Errare humanum est: frequency of laterality errors in radiology reports. AJR Am J Roentgenol. 2009;192(5):W239–W244. doi: 10.2214/AJR.08.1778. 
  2. ElGhrably I, Fraser S. An observational study of laterality errors in a sample of clinical records. Eye. 2008;22:340–343
  3. DiGiovanni CW, Kang L, Manuel J. Patient compliance in avoiding wrong-site surgery. J Bone Joint Surg Am 2003; 85-A(5): 815–819.