Larger columns and change of lysis buffer increase the yield of cell-free DNA extracted from amniotic fluid.

pending on the laboratory. Smaller laboratories analyze the sample on a direct ISE system for Na , K , and Cl , and then forward the remaining sample to the nearest laboratory in the network with the capacity for ultracentrifugation and analysis of the remaining requested test profile. In the larger laboratories equipped with Airfuges, the sample is ultracentrifuged, and all results, including Na , K , and Cl , are reported from the ultracentrifuged sample. The results are reported with a comment indicating that the results were obtained after ultracentrifugation to remove lipids. No lipid-clearing agents are used. In summary, hyperlipidemia caused errors in indirect ISE electrolyte measurements. All 3 electrolytes (Na , Cl , and K ) determined by the indirect ISE system were affected, showing artifactual decreases as a result of hyperlipidemia. The Na and Cl were decreased by 1 mmol/L and K by 0.04 mmol/L for each 10-mmol/L increase in total lipid concentration. When direct ISE methods and ultracentrifuges are unavailable to handle severely lipemic samples, corrective formulas can be used.