Study looks at blood clot risk for patients with HIV

HIV-positive individuals have an incidence of venous blood clots, including deep vein thrombosis (DVT) and pulmonary embolism, some ten-fold higher than that seen in the general population, according to research published in the July 1^st edition of the Journal of Acquired Immune Deficiency Syndromes. The investigators, from Johns Hopkins University, found that recent hospitalisation, use of a central venous catheter, and a CD4 cell count below 500 cells/mm³ were risk factors for the condition.

There is increasing evidence that patients with HIV have an increased risk of developing blood clots in their veins (venous thromboembolism). Such clots are associated with a risk of significant illness or death.

Earlier research suggests a two- to ten-fold increased risk of venous blood clots amongst patients with HIV and it has been estimated that the incidence of the condition in patients with HIV is between 0.3% - 2% per year.

Investigators from Johns Hopkins University reasoned that patients with HIV might have particular risk factors that increase their risk of developing venous blood clots. They therefore designed a case-controlled study to determine the incidence and risk factors for the condition.

They identified 160 HIV-positive patients with a confirmed venous blood clot who received care at their centre between 1989 and 2004. A total of 109 of these patients were diagnosed with DVT, with 39 having a pulmonary embolism. Each of these patients was matched with four HIV-positive patients who did not develop a venous blood clot.

Incidence

Consistent with earlier research, the investigators found an incidence of venous blood clots of 0.56% per year, ten times what they would expect to see in the general US population.

Risk factors

All the patients developing a venous blood clot were men, most (84%) were black and the mean age was 39 years.

In their first set of statistical analysis the investigators found that the following factors were more common amongst patients developing venous blood clots than in the controls patients:

• Black race (OR = 1.65; 95% CI, 1.11- 3.08).
• Age over 36 years (OR = 1.85; 95% CI, 1.21 – 2.83).
• CD4 cell count below 500 cells/mm³ (OR = 5.0; 95% CI, 2.4 – 10).
• Haemoglobin below 12g/dl (OR = 3.34; 95% CI, 2.2 – 5).
• Hospitalisation within the previous three months (OR = 21; 95% CI, 11 – 35).
• Hospitalisation with lymphoma (OR = 18; 95% CI, 4 – 83).
• Use of central venous catheter in the previous three months (OR = 17; 95% CI, 8.6 – 32).
• Use of mechanical ventilation within the previous three months (OR = 9.6; 95% CI, 3.73 – 25).

In their subsequent “multivariate” analysis, the following factors remained significantly related to venous blood clots:

• Age (every one year increase) (AOR = 1.05; 95% CI, 1.01 – 1.09).
• Hospitalisation in the previous three months (AOR = 13; 95% CI, 6.4 – 27).
• Central venous catheter in the previous three months (AOR = 6; 95% CI, 2.3 – 16).
• CD4 cell count below 500 cells/mm³ (AOR = 3; 95% CI, 1.2 – 7.8).

Neither viral load, nor use of antiretroviral drugs were associated with the risk of a venous blood clot.

The investigators call for further studies to clarify the risk of venous thromboembolism in patients with HIV. They believe that such research is particularly important as the already increased risk of this condition in patients with HIV “is expected to increase as this population ages.”

They conclude, “the mortality of pulmonary embolism is high, and morbidity in deep vein thrombosis is great. With tremendous recent gains in life expectancy for patients with HIV/AIDS, addressing the threat of venous thromboembolism is increasingly appropriate.”