One of the largest changes ICD-10-CM brought was laterality. Thousands of codes now distinguish right from left, and choosing the wrong one - or defaulting to unspecified - is a frequent and easily avoided error.
Which codes require a side
Laterality applies to conditions affecting paired organs and structures: eyes, ears, limbs, kidneys, lungs, breasts, ovaries, joints. Where the classification offers a side, the code set typically provides four options: right, left, bilateral, and unspecified.
Not every code has all four. Some conditions have no bilateral option because the condition cannot present that way; others have no unspecified option at all, which means the side must be documented before a valid code can be assigned.
Unspecified is a documentation problem, not a coding choice
When a laterality code exists and you select the unspecified option, you are recording that the medical record does not say which side. That is sometimes true, and in those cases the unspecified code is the honest and correct choice.
But it is often not true. The side is frequently documented elsewhere in the record - in the operative note, the imaging report, the nursing notes - even when the assessment line omits it. Reaching for unspecified without checking is the actual error. It costs specificity, and payers increasingly scrutinise unspecified laterality on conditions that almost always have a documented side.
If the record genuinely does not establish the side, the correct response is a provider query, not a guess. Assigning “right” because it is more common is fabrication, and it is a far more serious problem than an unspecified code.
Bilateral needs care
Where a bilateral code exists, use it rather than reporting the right and left codes separately. Reporting both individual sides when a bilateral code is available creates a duplicate-service appearance that can trigger denials.
Where no bilateral code exists, the opposite applies: report both the right and the left code. The classification is telling you it does not have a combined option.
Bilateral conditions that are later treated on one side only need attention as the episode progresses. If a bilateral condition is resolved on one side, the remaining condition is unilateral from that point, and the code should reflect what is true at the encounter being coded.
Laterality is about the patient, not the viewer
Right and left are always the patient's right and left. This sounds obvious and is nonetheless a real source of error when coding from imaging studies, which may be displayed from the viewer's perspective, or from photographs. When a report is ambiguous, the anatomical description in the body of the report governs.
Practical checks
- Does this condition have laterality options in the code set?
- Does the record state a side anywhere - not just in the assessment?
- If bilateral, does a combined code exist, or should both sides be reported?
- Is the side the patient's, and consistent across the record?
- If genuinely undocumented, is a provider query the right next step?
Related reading: when unspecified codes are acceptable.