What is the “code first” rule in medical billing and coding?
“Code first” is an ICD-10-CM sequencing coding guideline that instructs the medical coder to assign the underlying condition before coding the manifestation – that is, the secondary condition that results from the primary disease.
J91.8 Pleural effusion in other conditions classified elsewhere. J91.8 describes the manifestation of an underlying disease, not the disease itself.
Code First underlying disease, such as:
- Filariasis B74.0 – B74.9
- Influenza J09.X2, J10.1, J11.1
U09.9 Post COVID-19 condition, unspecified. Applicable to post-acute sequela of COVID-19.
Code First the specific condition related to COVID-19 if known, such as:
- Chronic respiratory failure J96.1
- Loss of smell R43.8
- Loss of taste R43.8
- multisystem inflammatory syndrome M35.81
- pulmonary embolism I26.-
- Pulmonary fibrosis J84.10
K31.84 Gastroparesis. Applicable to gastroparalysis.
Code First the underlying disease if known, such as:
- anorexia nervosa F50.0-
- diabetes mellitus E08.43, E09.43, E10.43, E11.43, E13.43
- Scleroderma M34.-
Why is “code first” often missed in medical coding?
Many clinicians are not trained in complex coding rules – they document diagnoses based on clinical relevance, not code sequencing. For the coder reviewing documentation downstream in their work queue it can result in:
- Unacceptable principal diagnosis (UPD)
- Significant time spent clarifying clinical details and correcting codes
- Claims rejected, resubmissions, or write-offs
Medical coders play a critical role in filling coding gaps by interpreting the clinical documentation correctly and applying sequencing rules appropriately.
How to avoid costly claim denials
Clinical terminology serves as the bridge between a clinician’s language and the standardized codes required for medical billing and reporting. IMO Health’s revenue cycle solution is built on consistently updated, proprietary content – that’s already within the EHR – and flags any problematic codes in real-time, prompting actionable corrections that are supported by clinical reasoning:
This approach leads to reclaimed coder time for higher-value work, reduced coder queries, enhanced provider coding education – and saved revenue.
What happens when you get medical coding right
After a short 90-minutue implementation of IMO Health’s revenue cycle solution, one small, private multispecialty medical group saw a 54% reduction in denials from non-primary codes used in “code first” within the first month.
