by centnifugation) was visibly turbid. In thesesamples the PLT increase attn but- able to lipemia was 47%. The cell-free plasma and the pooled human blood.
Letters
988
(Ci/Co) x 100 300
500
200Th.
400 100 300
1W
Coulter JS
0
10
20
30 (TGI (mmol/L)
Fig. 1. Interference from lipemia in PLT results from Technicon H3 and Coulter iS hematology analyzers for lntralipid-supplemented specimens and (Inset) specimens with chylomicrons added. x-axis, added triglyceride concentration from lntralipid or chylomicrons. Ci, apparent PLTcount in the presence of triglycerides, Co, platelet count in the absence of triglycerides. glyceride
concentration 1.6 ± 0.85 (range 0.52-5.3). The specimens were selected from the samples received at the laboratory for routine analysis, and we considered a blood sample lipemic when its plasma (obtained by centnifugation) was visibly turbid. In thesesamples the PLT increase attn butable to lipemia was 47%. The cell-free plasma and the pooled human blood showed similar increases in PLT when we added a similar amount of chylomicrons. No interference was observed for RBC and WBC in both hematology analyzers for added triglyceride concentrations up to 28.6 mmol/L. Because of the positive interference of lipemiaon PLT measurements by hematology analyzers that use light-scattering assays, we conclude that the clinical laboratories using these methods should inform the attending physicians about such interferences.
mmol/L
References 1. Creer MH. Ladenson J. Analytical error due to
Iipemia. LabMed 1983;14:351-5. 2. GronerW. Tycko DH. Characterizing blood cells by biophysical measurements in flow. Blood
Cells 1980;6:141-57. 3. Coulter WH. High-speedautomatic blood cell counter and cell size analyzer. Proc NatI Electron Conf 1956;12:1034-40. 4. NCCLS publication EP-7-P. Interference testing in clinical chemistry. Proposed guideline. Villanova, PA: National Committee for Clinical Laboratory Standards, 1986:341-4. 5. Tietz NW, ed. Fundamentals of clinical chemistry. 2nd ed. Philadelphia: WB Saunders, 1982:
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6. Statland BE, Winkel P, Harris SC, Burdsall Mi, Saunders AM. Evaluation of biological sources of variation of leukocyte counts and other hematologic quantities using very precise automated analyzers. Am J Clin Pathol 1978:69: 48-54. 7. Glick MR, Ryder KW, Jackson SA. Graphical comparisons of interferences in clinical chemistry
instrumentation.
Clin Chem
1986:
32:470-5. 8. Jay OW, Provasek D. Characterization and mathematical correction of hemolysis interference in selected Hitachi 717 assays. Clin Chem 1993:39:1804-10.
Miguel Cantero Jos#{233} R. Conejo Augustmn Jimenez* Servicio de Anal. ClIn. Hosp. General Univ. de Guadalajara Donantesde sangre,s/n 19002 Guadalajara,Spain
*
Author
forcorrespondence.
Bilirubin Interference with Determination of Creatlnine, Lactate, Phosphorus, and Uric Acid on Beckman Synchron CX7 To theEditor: Icteric samples constitute a realchallenge for laboratoriesin hospitals with a high frequency of hepatic diseases. Using a Beckman Synchron CX7 (software version 2.1; Beckman Instruments, Fullerton, CA), we have characterized bilirubin
interferenceon variables frequently measuredin the liver intensive-care unit, e.g.,1 creati nine,lactate, inorganicphosphorus, and uricacid. Experiments were performed on icteric specimens supplemented with creatinine (Eastman Kodak, Rochester, NY), L-( + )lactate (Boehringer Mannheim, Mannheim, Germany), phosphorus (as K2HPO4 . 3H20), or uric acid (Merck, Darmstadt, Germany) and on nonicteric specimens supplemented with either unconjugated bilirubin (Fluka Chemie, Buchs, Switzerland; UBIL, 0-800 j.LmoI/L) or the conjugated analog, ditaurobilirubin (Calbiochem, La Jolla, CA; DTB, 0-480 moVL). All measurements were conducted according to Beckman’s recommendations for the following Beckman test combinations: creatinine (ref.443340), uric acid (ref. 442785), lactate(ref. 445875), and phosphorus (ref.442790). Bilirubin interference results were expressed as the mean ± SD difference (Diff) between supplemented and unsupplemented samples. Results are shown in Table 1. UBIL 200 .tmol/L interfered negatively (-7% at 200 mol/L) with the creatinine assay #{216}affe method), the interference being proportional to the bilirubin concentrations: Diff,re*t = -0.062 UBIL + 5.38 (n = 36, P
