Risk factors for deep vein thrombosis in short-haul cockpit crews: a prospective study

Venous thrombosis is a concern receiving international attention, especially for passengers traveling on long distance flights. However, there are no data on the effect on cockpit crew of multiple short duration flights.

Cockpit crew flew two or more internal flights per day. At sign on, 15 ml of blood was venesected from the subjects; at sign off, 20 ml of blood was venesected. All flights originated and terminated at Johannesburg Airport. A full blood count, differential, and D-dimer levels were determined. All participants completed detailed questionnaires stating their ages, alcohol consumption 24 h prior to flight duty, the amount of liquid consumed during flying time, the number of times they went to the toilet, and the amount of time spent sitting during flights.

Blood tests on 27 cockpit crew were performed. D-dimers were reduced from 163 ng x ml(-1) to 133 ng x ml(-1) (p = 0.03). Hemoglobin levels dropped from 16.0 g x dl(-1) to 15.8 g x dl(-1) (p = 0.004). Hematocrit levels decreased from 47.2 ml x 100 ml(-1) to 46.9 ml x 100 ml(-1) (p = 0.04). Platelets increased from 221 x 10(9) x L(-1) to 241 x 10(9) x L(-1) (p = 0.001). White cell counts increased from 6.4 x 10(9) x L(-1) to 7.01 x 10(9) x L(-1) (p = 0.0063). Correlation analysis was performed between blood test results and the parameters of the questionnaire. No correlation was found between any of the parameters and the blood results.

There is no evidence of sub-clinical thrombotic events in this group of subjects. Cockpit crew who fly multiple short duration flights do not suffer sub-clinical thrombotic events as evidenced by an absence of increased D-dimers.