Correction Factors for Estimating Potassium Concentrations in Samples With In Vitro Hemolysis: A Detriment to Patient Safety by ProQuest


More Info
									          Correction Factors for Estimating Potassium
       Concentrations in Samples With In Vitro Hemolysis
                                            A Detriment to Patient Safety
              Mai M. H. Mansour, MS; Hassan M. E. Azzazy, PhD, DABCC; Steven C. Kazmierczak, PhD, DABCC

● Context.—Correction factors have been proposed for es-              75th, and 90th percentiles were calculated for each he-
timating true potassium concentrations in blood samples               molysis index category.
with evidence of in vitro hemolysis.                                     Results.—From our 2 models, we derived correction fac-
   Objective.—We used 2 different models of true (ie, non-            tors expressing an increase in potassium concentration of
simulated) in vitro hemolysis to evaluate the clinical utility        0.51 and 0.40 mEq/L for every increase in plasma hemo-
of correction factors for estimating potassium concentra-             globin concentration of 0.1 g/dL. These correction factors
tions in samples with evidence of in vitro hemolysis.                 are much higher than those reported in studies that sim-
   Design.—Potassium correction factors were derived us-              ulated in vitro hemolysis by freeze-thaw lysis or osmotic
ing 2 different models. In model 1, potassium and plasma              disruption of whole blood.
hemoglobin were measured with the Hitachi 747 analyzer                   Conclusions.—Use of correction factors for estimating
in 132 paired blood samples, with each pair consisting of
                                                                      the true potassium concentration in samples with evidence
1 sample with evidence of hemolysis and 1 without, col-
lected during the same phlebotomy procedure. The change               of in vitro hemolysis is not recommended. Derivation of
in measured potassium concentration was plotted versus                correction factors by using samples with nonsimulated in
the change in plasma hemoglobin concentration for each                vitro hemolysis suggests that the actual increase in potas-
pair of samples. In model 2, the potassium levels of                  sium in hemolyzed samples is much higher than that re-
142 784 blood samples and the corresponding hemolytic                 ported in previous studies that produced hemolysis with
index values were measured with the Beckman LX20 ana-                 artificial means.
lyzer. Potassium concentrations at the 10th, 25th, 50th,                 (Arch Pathol Lab Med. 2009;133:960–966)

T   he preanalytic phase of laboratory medicine is the
     phase that can most adversely affect the accuracy of
test results.1 Poor specimen quality is recognized as the
                                                                      samples and adjustment of the measured potassium result
                                                                      with a correction factor based on the magnitude of he-
most frequent source of error in this phase of the testing               Several studies have advocated using correction factors
process, with in vitro hemolysis accounting for the ap-               to account for the effect of in vitro hemolysis on measured
proximately 40% to 70% of samples received in the clinical            potassium concentrations.6–9 While correction factors may
chemistry laboratory that are unsuitable for analysis.2–4             help provide a better assessment of the true potassium
  Although many analytes are subject to interference ef-              concentration in patients, the variability in the correction
fects from in vitro hemolysis, the influence of hemolysis              factors that have been proposed is alarming. A variety of
on measured potassium concentrations is probably most                 issues may account for this difference, including the mech-
widely recognized. The frequency of potassium measure-                anism used to simulate in vitro hemolysis, interindividual
ments, along with the serious consequences of misdiag-                variability in erythrocyte hemoglobin concentrations, and
nosis of hypokalemia or hyperkalemia, has led to the de-              the effect of erythrocyte age on intracellular potassium
velopment of various options for handling hemolyzed                   concentrations.10,11 The variations in proposed correction
samples.4,5 These options include outright rejection of he-           factors suggest that adopting them to estimate potassium
molyzed samples, analysis of hemolyzed samples and the                concentrations may be inappropriate and not in the best
reporting of potassium levels with a disclaimer stating               interest of patient safety. To better assess the clinical utility
that the result may be incorrect, or analysis of hemolyzed            of correction factors, we investigated the effects of in vitro
                                                                      hemolysis by using 2 different models of true (ie, non-
                                                                      simulated) in vitro hemolysis. In addition, we compared
  Accepted for publication September 15, 2008.
  From the Department of Chemistry, American University in Cairo,
                                                                      the results of our investigations with those of other studies
Cairo, Egypt (Drs Mansour and Azzazy); and the Department of Pa-      that have derived correction factors by using a variety of
thology, Oregon Health & Science University, Portland, Ore (Dr Kaz-   different mechanisms to simulate in vitro hemolysis.
  The authors have no relevant financial interest in the products or
                                                                                      MATERIALS AND METHODS
companies described in this article.                                    We used 2 different models, 2 different instrument platforms,
  Reprints: Steven C. Kazmierczak, PhD, DABCC, Department of Pa-      and 2 different sample types to evaluate the effects of in vitro
thology, Oregon Health & Science University, 3181 SW Sam Jackson      hemolysis on measured potassium concentrations. Data were an-
Park Rd, L471, Portland, OR 97239 (e-mail: kazm
To top