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Patient Safety and Quality

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Diagnostic codes poorly identify deep vein thrombosis or pulmonary embolism after surgery from hospital claims

After surgery, patients run the risk of developing debilitating and life threatening blood clots. The Agency for Healthcare Research and Quality (AHRQ) offers hospitals a collection of Patient Safety Indicators (PSIs) as free software to help identify post-operative deep vein thrombosis and pulmonary embolism (DVT/PE) and other adverse events from billing or claims data that hospitals regularly collect. These indicators are developed, in part, by using the diagnostic codes.

AHRQ researchers Chunliu Zhan, M.D., Ph.D., James Battles, Ph.D., and Yen-pin Chiang, Ph.D., and David Hunt, M.D., Centers for Medicare & Medicaid Services (CMS), compared the diagnostic codes for DVT and PE against the gold standard of medical record extractions to determine the accuracy of the diagnostic codes for identifying DVT/PE.

The researchers reviewed nearly 21,000 surgery discharge records for 2002 to 2004 from CMS. The study found that every two in three DVT/PE cases identified with medical records were flagged by diagnostic codes. However, only one in three DVT/PE cases identified by diagnostic codes was confirmed by medical records. These results suggest that the diagnostic codes have limited ability to identify DVT and PE events after surgery.

AHRQ PSIs have been increasingly used as screening tools to study patient risks and to assess the effectiveness of hospital quality and safety programs. This study is a reminder that rigorous validation and revision are needed before the indicators can be used to assess patient safety or for public reporting.

One critical revision will be the inclusion of the "present-on-admission" codes in the AHRQ PSI algorithms. The researchers stressed that adding "present-on-admission" codes to the diagnostic codes, which the Deficit Reduction Act of 2005 mandated CMS to implement in Medicare billing by October 1, 2007, will substantially improve the PSI's accuracy in identifying DVT/PE and other adverse events from hospital claims.

See "The validity of ICD-9-CM codes identifying postoperative deep vein thrombosis and pulmonary embolism," by Dr. Zhan, Dr. Battles, Dr. Chiang, and others in the June 2007 The Joint Commission Journal on Quality and Patient Care 33(6), pp. 326-331.

Reprints (AHRQ Publication No. 07-R074) are available from the AHRQ Publications Clearinghouse.


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