Optimal practice for CSF collection and processing
| Confounding variable | Ideal situation |
|---|---|
| Preanalytical factors | |
| Time of collection | 8:00–12 noon to avoid potential for diurnal variation in CSF biomarkers |
| LP needle | Needle gauge or design not known to influence measured biomarker concentration but gauge is related to risk of post-LP headache. Smallest size practical to use in diagnostic LP is 22G. Atraumatic needles are associated with reduced post-LP headache but increased failure rate |
| Use of lumbar catheters/manometers | Aβ1-42 may adhere—to be avoided, if possible |
| Collection vessel | Polypropylene tube recommended. Aβ1-42 and other proteins adhere to polystyrene and glass significantly reducing measured concentrations. Tube brand may also influence measured biomarker concentrations |
| Fasting | Not required |
| Blood contamination/blood–brain barrier dysfunction | Blood contamination of up to 5000 erythrocytes/µL cells does not alter measured biomarker concentration, but blood–brain barrier dysfunction equivalent to CSF/serum albumin ratio >11 results in reduced measured Aβ1-42 concentration and should be interpreted with care |
| Optimal volume | In addition to CSF collected for routine clinical examination (eg, cell count, oligoclonal bands, cytology, etc) 15 mL can safely be collected without increased risk of post LP headache |
| Centrifugation | Within 30 min of LP at 3000 rpm for 10 min to remove cells and other debris |
| Aliquot storage volume | Samples that are frozen prior to analysis should be stored in aliquots of a standardised volume which fits the tube size well. Specifically, one should strive for as high volume to surface ratio as possible (well-filled tubes). Volume to surface ratio and number of tube transfers influence measured Aβ1-42 concentration, probably due to protein adsorption |
| Freeze thawing | One or less freeze thaw cycles is recommended. Measured Aβ1-42 concentration drops by 20% after 3 freeze thaw cycles. Aβ1-42 and τ concentrations are stable at temperatures of −80°C |
| Choice of immunoassay/platform | Consistency required; variability in commercially available ELISA-based assays, calibration peptides and platforms mean interlaboratory and interassay consistency is poor |
CSF, cerebrospinal fluid; LB, lumbar puncture.