Heat illness is filling more emergency departments than it did in previous years, and the paperwork that follows those visits is where many medical practices lose revenue.
Summer spikes in heat‑related visits
During the 2023 warm season, heat‑related illness accounted for a larger share of emergency department visits than in the five prior years, according to the report. The increase was most pronounced among men and adults aged 18 to 64. Those visits often arrive with coding requirements that differ from the routine winter respiratory care most practices handle.
In addition to heat exhaustion, clinicians see a rise in sunburns, tick bites and fireworks injuries. Each of these conditions falls under the injury and external cause chapters of the ICD‑10‑CM system, which demand a high level of specificity. A missing seventh character, an absent laterality indicator, or an external cause code placed in the wrong position can cause a claim to be rejected.
ICD‑10 chapters drive summer coding complexity
Chapter 19, covering injury, poisoning and certain other consequences of external causes, accounted for 213 of the 487 new diagnosis codes in the FY2026 update that took effect on Oct. 1, 2025. That is more than any other chapter and nearly double the next largest, according to a breakdown by the coding audit firm Health Information Associates. The same chapter is the one most practices encounter during the summer months.
For example, a tick bite is not automatically classified as Lyme disease. The CDC reported that Lyme disease peaked in late June, with 62,551 cases reported in 2022, most of them concentrated in 15 high‑incidence states. Outpatient guidelines prohibit coding an uncertain diagnosis as confirmed, so a visit for a site‑specific insect bite with an external cause code is necessary. The confirmed‑Lyme codes in the A69.2 family are used only after serology and clinical findings support the diagnosis. Jumping straight to A69.20 on suspicion can trigger an audit finding.
Fireworks injuries illustrate another common pitfall. Roughly two‑thirds of annual fireworks injuries cluster around the weeks of July 4, according to the Consumer Product Safety Commission, with teenagers and young children most affected. The injury itself—burn or laceration—should lead the claim, while the firework discharge code that explains how it happened belongs in a secondary position. When coders reverse that order, the claim often bounces because external cause codes never lead.
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Across heat, water, bites and sports injuries, the recurring issue is sequencing and specificity, not the clinical diagnosis itself. Coding heat exhaustion as plain dehydration undercuts medical necessity for the fluids given. Labeling swimmer’s ear without specifying the side triggers a laterality edit that many payers now enforce. Recording a venomous sting as a non‑venomous insect bite omits the toxic effect code that should appear first.
These gaps are not hard calls at the point of care; they are documentation and workflow lapses that surface weeks later as denials.
From a practical standpoint, the impact falls most heavily on clinics that rely on timely reimbursement to stay afloat. When a claim is delayed or denied, the practice must spend additional staff hours chasing payments, which can erode profit margins already squeezed by seasonal staffing needs.
Steps practices can take before claims leave the office
Front‑desk verification can catch sports and camp physical visits that many plans treat as non‑covered, turning an August write‑off into a collected self‑pay charge. A standing reminder about seventh characters and laterality helps prevent malformed codes that clearinghouses reject outright. Ensuring external cause codes sit in the secondary position, where they belong, clears one of the most common summer rejections before the claim even leaves the practice.
They have assembled a summer coding handbook that covers heat illness, sun and skin conditions, bites and stings, tick‑borne disease, water injuries, sports injuries, foodborne illness and the preventive visits that crowd summer schedules. The handbook lists the ICD‑10‑CM codes, documentation cues and denial traps for each condition, and every code was verified against the FY2026 code set.
By integrating these checks into routine workflows, clinics can reduce the number of rejected claims and improve cash flow during the busy summer months.
