R78 ICD-10-CM Code: Findings of drugs and other substances, not normally found in blood

R78 is the ICD-10-CM diagnosis code for findings of drugs and other substances, not normally found in blood. R78 sits in the ICD-10-CM chapter for symptoms, signs and abnormal clinical and laboratory findings, not elsewhere classified (r00-r99), within the section covering abnormal findings on examination of blood, without diagnosis (r70-r79).

Header codes like R78 cannot be reported on claims directly, they organize child codes that share clinical context but the actual diagnosis must be coded to the highest level of specificity supported by the documentation. Coders should look at R78's child codes and select the one that matches the patient's documented presentation, since payers reject header codes submitted as the primary diagnosis. For risk adjustment workflows, header codes never contribute to a Medicare Advantage member's RAF score on their own; only billable child codes that happen to map to a payment HCC affect risk-adjusted plan payments.