Incidence of traumatic lumbar punctures in adults: the impact of a patient's first procedure.

INTRODUCTION: Lumbar puncture (LP) is a widely used diagnostic method in patients of all ages. Blood-contaminated cerebrospinal fluid samples are frequent and may compromise diagnostic accuracy. OBJECTIVES: We determined age-specific incidences of traumatic LPs (TLPs) in adults and examined factors that accounted for the incidence of TLPs. METHODS: Erythrocyte count data from 15,812 LP procedures (2,404 were performed twice) were collected from hospital records of patients aged from 18 to 104 years. The incidence of TLPs in a patient's second LP procedure was evaluated with logistic regression analysis using the first LP, the time between the procedures and age as predictors. RESULTS: The incidence of TLP in the second procedure was at least double that in the first procedure. If the first procedure was traumatic, the odds ratio of a TLP in the second procedure was 7-40-fold. One day between the successive procedures was associated with an over 10-fold odds ratio increase of TLP, and a week was still 4-8-fold odds ratio increase. Age was also associated with the incidence of TLP. CONCLUSIONS: Two factors (a week or less between a patient's two LP procedures or a traumatic first LP) multiply the odds of the second procedure being traumatic and contribute to whether a patient's following LP procedure is successful.