Lumbar drains can affect CSF biomarker levels

Tau and Aβ1–42 are two conventionally measured cerebrospinal fluid (CSF) biomarkers that can assist with the diagnosis of neurodegenerative disease. In Alzheimer’s disease, a high CSF total-tau (T-tau) concentration reflects neuroaxonal degeneration/injury and low CSF Aβ1–42 correlates with senile plaque pathology.1 There is evidence that these markers could be useful in the diagnosis of normal pressure hydrocephalus (NPH). In NPH, lumbar CSF levels of Tau and Aβ1–42 are typically low or low/normal (respectively), and could potentially discriminate from Alzheimer’s disease, in addition to being a putative prognostic marker for shunt responsiveness.2 3 When measured in the context of investigating NPH, CSF is usually sampled from the lumbar drain (LD), in situ as part of the diagnostic protocol.4 Increasingly lumbar drains are also being used in study protocols to obtain longitudinal biomarker results (to avoid multiple lumbar punctures (LP)).5 CSF transfer between collection tubes is known to reduce the overall concentration of Aβ1–42 by 25% due to adsorption to the ionic surfaces.6 It is unclear if the same effect is observed when CSF is sampled from lumbar drain. We investigated the effect of both silver-lined (Silverline, Spiegelberg) and barium-impregnanted (EDM, Medtronic) lumbar catheters, versus LP on concentrations of Aβ1–42 and T-tau in …