Venous Thromboembolism Rates Climb After Hospital Discharge

HAMILTON, Ontario, July 23 -- Patients are more likely to develop venous thromboembolism after hospital discharge than during their stay, and most get no prophylactic treatment.

Although as many as 10% of hospital deaths can be attributed to pulmonary embolism, most cases of venous thromboembolism are diagnosed in the three months after hospital discharge, Frederick A. Spencer, M.D., of McMaster University here, and colleagues, reported in the July 23 issue of the Archives of Internal Medicine.

The findings emerged from a study of 1,897 patients with an episode of venous thromboembolism confirmed from medical records of in the Worcester, Mass., metropolitan area during 1999, 2001, and 2003.

In all, 73.7% (1,399 patients) developed venous thromboembolism as outpatients. By comparison, only 26% (498 patients) developed the clots while hospitalized.

A substantial proportion of these outpatients had undergone surgery (23.1%) or hospitalization (36.8%) in the preceding three months. The median and mean lengths of those stays were 4.0 and 7.4 days.

Among those patients, 67% experienced deep vein thrombosis within a month of hospitalization.

Of patients who had recently been hospitalized but had not had surgery, 6.9% were diagnosed within one month after discharge, 19.9% between one and two months, and 13.2% between two and three months of discharge.

Among surgical patients, 66.4% were diagnosed with a clot within one month, 18.3% between one and two months, and 15.2% between two and three months after discharge.

Other major risk factors for venous thromboembolism in the outpatient setting included active malignant neoplasm (29.0%) or previous venous blood clot (19.9%).

Among 516 patients with a recent hospitalization who subsequently developed venous thromboembolism, fewer than half (42.8%) had been given anticoagulant prophylaxis during their hospitalization, while 16.9% received only non-pharmaceutical prevention. Of these patients, only three of five (59.7%) had received any form of therapy (drug or mechanical) while hospitalized.

Because most of the cases occurred within 29 days of hospital discharge (and 41% within 14 days), it is not unreasonable to assume that some of these cases might have been prevented by increasing appropriate in-hospital prophylaxis, such as compression stockings, pneumatic compression devices, and, in high-risk patients, anticoagulants, the researchers said.

Discussing the study's limitations, the researchers noted that, as in any observational study, the chart study could have missed some cases among patients who seek care outside the study area. Furthermore, documentation of these conditions came from medical records, leaving the possibility of over- or underestimation.

Further characterization of this high-risk patient profile in additional observational studies will generate subsequent investigations that will ultimately reduce the number of these failures, the researchers concluded.

A meta-analysis published in the same issue found that both unfractionated heparin and low molecular weight heparin reduced the risk of thromboembolism in hospitalized medical patients.

When compared directly with unfractionated heparin, low molecular weight heparin was associated with a 32% lower risk of deep vein thrombosis (RR, 0.68), said Henry Krum, M.B.B.S., Ph.D., of Monash University in Melbourne, Australia, and colleagues.

But they found no difference between the two agents in the risk of bleeding or thrombocytopenia.

The researchers' analysis of 36 randomized controlled trials compared more than 48,000 hospitalized medical patients given unfractionated heparin or low molecular weight heparin with a control or with each other.

Unfractionated heparin (5,000 units three times daily) was more effective than the same dosage twice daily in preventing deep vein thrombosis (risk ratio [RR], 0.27; 95% CI, 0.20-0.36; versus RR, 0.52; 95% CI, 0.28-0.96).

Compared with the controls, unfractionated heparin was associated with a reduced risk of both deep vein thrombosis (RR 0.33; CI, 0.26-0.42) and pulmonary embolism (RR, 0.64; CI, 0.50-0.82).

This was also true for low molecular weight heparin (RR,0.56; CI, 0.45-0.70; and RR, 0.37; 95% CI, 0.21-0.64, respectively).

However, neither drug reduced mortality, the researchers reported.

"I predict that preventing outpatient venous thromboembolism will be the 'hot button' issue in 2008," said Samuel Z. Goldhaber, M.D., of Harvard in an editorial. "We must start collecting relevant data at the time of hospital discharge so that we can provide these vulnerable patients with proper and comprehensive venous thromboembolism prophylaxis."

Proper prophylaxis requires evidence-based measures applied according to protocols used in randomized controlled trials, he said. For pharmacological prophylaxis, this means ordering the right dose of the right medication at the right time for the proper duration (which may span the hospitalization and the early period after hospital discharge).

Breaking down artificial barriers between outpatient and inpatient prophylaxis are vital first steps, Dr. Goldhaber concluded.

Institute.

Dr. Krum reported no financial conflicts. His study was supported by a Centre of Clinical Research Excellence grant from the National Health and Medical Council of Australia.

Dr. Goldhaber reported no financial conflicts.