The effect of plasmapheresis on the concentration of certain plasma proteins: a case identified by an inaccurate LDL-cholesterol estimation

Ann Clin Biochem 2008;45:436-439
© 2008 Association for Clinical Biochemistry


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Case Reports

O C Maguire1,
D Mc Carthy2 and
S K Cunningham1

1 Department of Clinical Biochemistry;
2 Department of Haematology, St Vincent’s University Hospital, Dublin 4, Ireland

Corresponding author: Ms Orla Maguire. Email: o.maguire{at}

A 35-year-old man was found to have a negative LDL-cholesterolconcentration (–0.05 mmol/L) when estimated on a fastingplasma sample using the Friedewald equation. Plasma urea, electrolytesand liver function tests (LFTs) were normal except for a raisedtotal bilirubin of 74 µmol/L. Haematological results showedboth a low haemoglobin and fibrinogen concentration. It transpiredthat the patient had undergone daily plasmapheresis treatmentson the previous four days; plasma had been exchanged with a5% albumin solution. He had been diagnosed with Evan’s syndromepreviously (characterized by autoimmune haemolytic anaemia)and had been admitted with severe anaemia, which had provedunresponsive to conventional treatments. The concentration ofmost plasma substances is reduced by 50–60% after onestandard plasmapheresis treatment, with the rate of return tosteady state concentrations varying among analytes. The findingof a negative LDL-cholesterol concentration (arising primarilyas a result of normal triglyceride concentrations) may reflectthe more efficient removal of LDL and HDL lipoproteins duringthe plasmapheresis procedure (PP) than lipoproteins containingproportionally more triglycerides. Plasma lipids, total protein,immunoglobulins and transferrin had recovered to steady stateconcentrations by eight days post-plasmapheresis, whereas caeruloplasminconcentrations had not. This case report illustrates the difficultiesof obtaining accurate information on the steady state concentrationsof plasma analytes, in particular protein bound substances,when analysis is carried out on a sample from a patient thathas recently undergone plasmapheresis. The normal plasma albuminin this situation did not flag the possibility of the samplebeing artefactually diluted.

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