A guide to the most common ICD-10-CM coding errors medical coders make — including unspecified codes, sequencing mistakes, missing diagnoses, POA errors, and laterality issues — and how to prevent them.
Medical coding errors cost the U.S. healthcare system billions of dollars annually in claim denials, underpayments, overpayments, and compliance penalties. For individual practices and health systems, a single coding error on a high-value claim can mean thousands of dollars in lost revenue or repayment obligations.
Understanding the most common ICD-10-CM coding errors — and how to avoid them — is one of the most valuable skills a medical coder can develop. Many of these errors are systematic and preventable with the right knowledge and workflow.
One of the most pervasive errors in ICD-10-CM coding is using unspecified codes when more specific information is available in the medical record. ICD-10-CM was specifically designed to capture far greater clinical specificity than ICD-9-CM, and payers have become increasingly sophisticated at identifying patterns of unspecified code usage.
Common examples of over-used unspecified codes:
Rule: Always code to the highest level of specificity supported by the medical record documentation. If the documentation supports a more specific code, use it.
Incorrect diagnosis sequencing is a common and costly error, particularly in the inpatient setting where DRG assignment depends on the principal diagnosis.
Frequent sequencing mistakes include:
Failing to capture all relevant secondary diagnoses is one of the leading causes of underpayment in the inpatient setting. Secondary diagnoses that meet the UHDDS definition — conditions that affect patient care in terms of requiring additional clinical evaluation, therapeutic treatment, or extended length of stay — must be coded.
Commonly missed secondary diagnoses include:
ICD-10-CM assumes a causal relationship between hypertension and heart disease, and between hypertension and CKD. However, coders sometimes incorrectly assume causal relationships in other situations where the guidelines do not support it.
You cannot assume a condition caused another condition unless the ICD-10-CM guidelines explicitly state a presumed relationship, or the physician has documented it. When in doubt, query the physician.
Different encounter types require different coding approaches. Common errors include using inpatient coding rules on outpatient claims, and vice versa.
ICD-10-CM requires laterality — specifying left, right, or bilateral — for many conditions. Failing to code the correct laterality is a common error that can affect claim adjudication.
If laterality is not documented in the medical record and cannot be clinically determined, query the provider. Do not default to "unspecified" without first attempting to obtain the information.
Present on Admission errors are particularly costly in the inpatient setting because they affect Hospital-Acquired Condition (HAC) penalties and quality reporting. Common POA errors include:
ICD10Source displays sequencing rules, POA exempt flags, CC/MCC designations, and age/sex restrictions directly alongside every code. Using a reference tool that surfaces these flags during the coding process can significantly reduce common errors before they reach the claim.
The information in this guide is based on official U.S. government publications. Always verify coding information against the most current official sources before use in billing or clinical documentation.
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