The effect of a fat emulsion on some common clinical chemical analyses

During infusion of fat emulsion serum becomes turbid. Turbidity interferes in various photometric serum analyses delaying urgent therapeutic decisions. Small laboratories may lack access to an ultracentrifuge to clear turbid samples. To identify the analyses mostly disturbed we collected serum samples containing various concentrations of the compounds or activities commonly requested by the intensive care unit (ICU) and spiked the samples with Intralipid (Kabi Vitrum, Sweden). Glycerol measurements were used as estimate of the amount of Intralipid prevailing in turbid serum. Applying the common instruments Astra 8 (Beckman) and RA 1000 (Technicon) sodium, potassium, phosphate, calcium, creatinine, urea, total bilirubin, amylase, lactate dehydrogenase and albumin were not sensitive to interference. Magnesium and creatinine were slightly lowered whereas glucose was increased. Aspartate amino transferase was not measurable. We suggest (a), that ICU contact the clinical chemistry laboratory to clarify what analyses will be hampered by turbidity in the inhouse instruments; and (b), that high serum glycerol values may be indicative of erroneous results in these analyses; and (c) that charts with confidence limits be established to aid recognition of the magnitude and direction of the errors.