R18.0Malignant ascites

R18.0 is the ICD-10-CM diagnosis code for malignant ascites. It belongs to category R18 (ascites), block R10-R19 (symptoms and signs involving the digestive system and abdomen) and chapter 18 (symptoms, signs and abnormal clinical and laboratory findings, not elsewhere classified). It is billable, so it can be reported on its own for dates of service from October 1, 2026 through September 30, 2027.

Within R18 (ascites), R18.0 is specifically for malignant ascites. Related codes cover other ascites (R18.8).

Code first malignancy, such as: malignant neoplasm of ovary (C56.-) and secondary malignant neoplasm of retroperitoneum and peritoneum (C78.6).

As a secondary diagnosis it is a CC (complication or comorbidity), which can move an inpatient stay into the "with CC" MS-DRG of its family, unless the principal diagnosis excludes it.

In MS-DRG v44.0, it is part of the grouping logic for DRG 947 (Signs and Symptoms with MCC, relative weight 1.261) and DRG 948 (Signs and Symptoms without MCC, relative weight 0.7835), in MDC 23 (Factors Influencing Health Status and Other Contacts with Health Services), as a principal or secondary diagnosis. The DRG a claim lands in depends on the principal diagnosis, procedures and any CC/MCC secondary diagnoses.

It is not acceptable as the principal diagnosis for an inpatient stay; it may be reported as a secondary diagnosis.

It has been part of ICD-10-CM since the code set took effect on October 1, 2015 and hasn't changed since.

Before ICD-10, this condition was coded in ICD-9-CM as 789.51 (malignant ascites).