Correction of factitious hyperkalemia in hemolyzed specimens.
BACKGROUND
Hemolysis in pediatric specimens is common due to difficult blood draws and small-bore intravenous catheters. Values of serum K+ become falsely elevated secondary to release of intracellular contents. If a reliable correction factor existed for this factitious elevation, repeat K+ measurements might be avoided.


OBJECTIVE
The aim of the study was to establish a correction factor for factitiously elevated K+, using free plasma hemoglobin (p-Hgb) as a measure of in vitro hemolysis.


METHODS
Twenty whole-blood specimens drawn from healthy adults via a 23-gauge needle were divided into 4 aliquots: (1) no manipulation, (2) mechanical hemolysis via a 27-gauge needle, (3) addition of potassium acetate (KAc), and (4) addition of KAc and mechanical hemolysis. KAc was added to mimic potentially significant hyperkalemia. All specimens had standard K+ and p-Hgb measurements performed.


RESULTS
Nonhemolyzed and hemolyzed K+ ranged from 3.2 to 8.1 mEq/L and 3.5 to 10.0 mEq/L, respectively. A linear relationship existed between the change in K+ and p-Hgb from the nonhemolyzed to hemolyzed specimens. A correction factor for K+ of 0.00319 (95% confidence interval, 0.00290-0.00349) x p-Hgb was obtained.


CONCLUSIONS
A reliable correction factor for factitious hyperkalemia in a clinically relevant range exists. By example, using the above correction factor, one can predict that the delta K+ in a specimen with 500 mg/dL of p-Hgb will be 1.6 mEq/L (range, 1.5-1.7). We suggest that when the lower bound of the predicted delta K+ results in a corrected value within the reference range, a second blood draw is unnecessary.
Owens
Heather
H
Department of Pediatrics, The Children's Hospital, Denver, CO 80218, USA. owens.heather@tchden.org
Siparsky
Georgette
G
Bajaj
Lalit
L
Hampers
Louis C
LC
D000293:Adolescent; D000328:Adult; D000465:Algorithms; D006454:Hemoglobins / Q000378:metabolism*; D006461:Hemolysis / Q000502:physiology*; D006801:Humans; D016014:Linear Models; D011188:Potassium / Q000097:blood*; D019347:Potassium Acetate; D012016:Reference Values; D015203:Reproducibility of Results
D006454:Hemoglobins; D019347:Potassium Acetate; D011188:Potassium