Correction of factitious hyperkalemia in hemolyzed specimens

Determination of the Optimal Wavelength of the Hemolysis Index Measurement

Many biochemical auto-analyzers have methods that measure the hemolysis index (HI) to quantitatively assess the degree of hemolysis. Past reports on HI are mostly in vitro studies. Therefore, we evaluated the optimal wavelength of HI measurement ex vivo using clinical samples. Four different wavelengths (410/451 nm: HI-1, 451/478 nm: HI-2, 545/596 nm: HI-3 and 571/596 nm: HI-4) were selected for HI measurement, and correlations were examined from the measurement results of 3890 clinical samples. Another set of 9446 clinical samples was used to examine the correlation of HI with lactate dehydrogenase (LDH), aspartate aminotransferase (AST) and potassium (K). Strong correlations were found between HI-4 and HI-1 and between HI-4 and HI-3. HI-1 and HI-2 cannot correctly assess hemolysis for high bilirubin samples, and HI-3 cannot correctly assess hemolysis for high triglyceride samples. LDH, AST and K correlated positively with HI-4 in clinical samples. For every 1-unit increase in HI-4, LDH increased by 19.51 U/L, AST by 1.03 U/L and K by 0.061 mmol/L, comparable to reports of other studies. In clinical samples, HI-4 was less susceptible to bilirubin and chyle and reflected well the changes in LDH, AST and K caused by hemolysis. This suggested that the optimal wavelength for HI measurement is 571 nm.

Hyperkalemia in a Hemolyzed Sample in Pediatric Patients: Repeat or Do Not Repeat?

OBJECTIVE

The aim of the study is to analyze whether repeat testing is necessary in healthy children presenting to a pediatric emergency department (ED) who are found to have hyperkalemia on a hemolyzed specimen.

METHODS

A 5-year retrospective analysis of pediatric ED patients found to have elevated potassium values on laboratory testing of a sample reported to be hemolyzed. All patients aged 0 to 17 years who had an elevated potassium level after an intravenous draw resulted from a serum sample that was reported as hemolyzed during an ED visit were included in the study.

RESULTS

One hundred eighty-seven patients with some degree of both hemolysis and hyperkalemia were included in the final analysis. The median age was 1.9 years of age. The most common race among all patients was White, followed by African American, and Asian. One hundred forty-five children had repeat sampling for hemolyzed hyperkalemia, 142 children, 97.9% (95% confidence interval, 95.6%-100%) had a normal potassium on repeat and 3 children, 2.1% (95% confidence interval, 0.0%-4.4%) had true hyperkalemia. The frequency of true hyperkalemia in our study population was 2% (3/145). All 3 of these patients had underlying conditions that would appropriately have raised clinician suspicion for hyperkalemia.

CONCLUSIONS

It may be unnecessary to obtain repeat samples to confirm normal potassium in a hemolyzed sample with normal blood urea nitrogen and creatinine.

What is the best wavelength for the measurement of hemolysis index?

BACKGROUND

Hemolysis is a common problem in the handling of serum specimens. The hemolysis index (HI) provides a warning of hemolysis in auto-analyzers. However, HI has not been standardized, and each laboratory's original method is applied. Especially, the wavelength used for HI measurement is different in each laboratory. Thus, we investigated the warning ability of HI at various wavelengths.

METHODS

We selected 4 wavelength types, and each HI was measured and calculated (410 nm/HI-1, 451 nm/HI-2, 545 nm/HI-3, and 571 nm/HI-4). To compare the 4 HI types, we investigated the influence of 3 interference components using artificially hemolyzed specimens (AHSs). We also investigated both the relationship between HI and hemoglobin concentration (Hb) and that between HI and 31 biochemical test values in AHSs.

RESULTS

In the interference assessment, only HI-4 showed no influence on the 3 interference components. The correlation between Hb and HI-4 was very strong (r_S = 0.9987). A 1-unit increase in HI-4 corresponded to a 14.8-mg/dL increase in Hb.

CONCLUSION

We found the best wavelength for HI to be at or near 571 nm.

Effect of Blood Cell Subtypes Lysis on Routine Biochemical Tests

BACKGROUND

The aim of this study is to establish the contribution of blood cells subtypes on hemolysis.

METHODS

Separated blood cell subtype suspensions prepared with blood from 10 volunteers were serially diluted to obtain different concentrations of cell suspensions. The cells were fully lysed and cell hemolysates were added (1:20) to aliquots of serum pool. Thus, seven serum pools with different concentrations of interferent were obtained for each blood cell subtype. Biochemical parameters and serum indices were measured by an autoanalyzer. As cell lysis markers, free hemoglobin was measured by spectrophotometry while myeloperoxidase and ᵝ-thromboglobulin were measured by enzyme immunoassay. The percent changes in analyte levels of the serum pools were evaulated by Wilcoxon Signed Rank Test and compared with clinical thresholds defined for each test.

RESULTS

The clinical thresholds were exceeded in lactate dehydrogenase, potassium, aspartate aminotransferase, creatine kinase, magnesium, total protein, total cholesterol, inorganic phosphate, glucose for red blood cells (RBC); lactate dehydrogenase, aspartate aminotransferase, total protein, inorganic phosphate and glucose for platelets (PLT). Free hemoglobin was significantly correlated with RBC (r=0.999; p=0.001), while myeloperoxidase and b thromboglobulin showed no significant correlation to white blood cells (WBC) and PLT, respectively.

CONCLUSIONS

The effect of RBC hemolysis in serum on the routine biochemical tests are clearly established, yet, additional studies are required in order to verify this kind of effects of PLT and WBC hemolysis.

Acute kidney injury in the fetus and neonate

Acute kidney injury (AKI) is an under-recognized morbidity of neonates; the incidence remains unclear due to the absence of a unified definition of AKI in this population and because previous studies have varied greatly in screening for AKI with serum creatinine and urine output assessments. Premature infants may be born with less than half of the nephrons compared with term neonates, predisposing them to chronic kidney disease (CKD) early on in life and as they age. AKI can also lead to CKD, and premature infants with AKI may be at very high risk for long-term kidney problems. AKI in neonates is often multifactorial and may result from prenatal, perinatal, or postnatal insults as well as any combination thereof. This review focuses on the causes of AKI, the importance of early detection, the management of AKI in neonates, and long-term sequela of AKI in neonates.

Do hemolyzed potassium specimens need to be repeated?

BACKGROUND

In the emergency department (ED), hyperkalemia in the presence of hemolysis is common. Elevated hemolyzed potassium levels are often repeated by emergency physicians to confirm pseudohyperkalemia and to exclude a life-threatening true hyperkalemia.

OBJECTIVES

We hypothesize that in patients with a normal renal function, elevated hemolyzed potassium, and normal electrocardiogram (ECG), there may not be a need for further treatment or repeat testing and increased length of stay.

METHODS

Data were prospectively enrolled patients presenting to the ED from July 2011 to February 2012. All adult subjects who had a hemolyzed potassium level ≥ 5.5 mEq/dL underwent a repeat potassium level and ECG. The incidence of true hyperkalemia in this population was measured.

RESULTS

A total of 45 patients were enrolled. The overall median age was 52 years (range 25-83 years); 22 were female (49%). In patients with hyperkalemia on initial blood draw and glomerular filtration rate (GFR) ≥ 60 (n = 45), the negative predictive value was 97.8% (95% confidence interval [CI] 88.2-99.9%). When patients had hyperkalemia on initial blood draw, GFR ≥ 60, and a normal ECG (n = 42), the negative predictive value was 100% (95% CI 93.1-100%).

CONCLUSIONS

In the setting of hemolysis, GFR ≥ 60 mL/min in conjunction with a normal ECG is a reliable predictor of pseudohyperkalemia and may eliminate the need for repeat testing. In patients with a normal GFR who are otherwise deemed safe for discharge, our results indicate there is no need for repeat testing.

Correcting laboratory results for the effects of interferences: an approach incorporating uncertainty of measurement

BACKGROUND

Results of numerical pathology tests may be subject to interference and many laboratories identify such interferences and withhold results or issue warnings if clinically erroneous results may be issued. Some laboratories choose to correct for the effect of interferences, with the uncertainty of the correction noted as a limitation in this process. We investigate the effect of correcting for the effect of interferences on the ability to release results within defined error goals using the effect of in-vitro haemolysis on serum potassium measurement as an example.

METHODS

A model was developed to determine the uncertainty of a result corrected for the effect of an interferent with a linear relationship between concentration and effect. The model was used to assess the effect of correction on the results which could be released within specified accuracy criteria.

RESULTS

Using the effects of haemolysis on potassium results as an example, the maximum amount of haemolysis in a sample that would change the result by > 0.5 mmol/L, with a frequency of 5%, was increased from approximately 1100 mg/L (no correction) to 8000 mg/L (with correction).

CONCLUSIONS

With modelling of the factors related to the uncertainties of results in the presence of interferences, it is possible to release results in the presence of significantly higher concentrations of interferences after correction than without correction. Correction of a result for a known bias and allowance for the uncertainty of the correction can be considered consistent with the guide to the expression of uncertainty in measurement (GUM).

Implications of the incidentalome for clinical pharmacogenomics

Incidental findings have long posed challenges for healthcare providers, but the scope and scale of these challenges have increased with the introduction of new technologies. This article assesses the impact of incidental findings on the introduction of prospective pharmacogenomic testing into clinical use. Focusing on the challenges of the incidentalome, the large set of incidental findings potentially generated through genotyping, the paper argues that provisional approaches to managing incidental findings may be implemented if necessary to allow benefits of pharmacogenomic testing to be realized in the clinical setting. In the longer term, approaches to returning incidental findings may need to focus on limiting the number of incidental findings to a number that can be addressed by patients and providers.

Potassium abnormalities in a pediatric intensive care unit: frequency and severity

BACKGROUND

Potassium abnormalities are common in critically ill patients. We describe the spectrum of potassium abnormalities in our tertiary-level pediatric intensive care unit (PICU).

METHODS

Retrospective observational cohort of all the patients admitted to a single-center tertiary PICU over a 1-year period. Medical records and laboratory results were obtained through a central electronic data repository.

RESULTS

A total of 512 patients had a potassium measurement. Of a total of 4484 potassium measurements, one-third had abnormal values. Hypokalemia affected 40% of the admissions. Mild hypokalemia (3-3.4 mmol/L) affected 24% of the admissions. Moderate or severe hypokalemia (K <3.0 mmol/L) affected 16% of the admissions. Hyperkalemia affected 29% of the admissions. Mild hyperkalemia (5.1-6.0 mmol/L) affected 17% of the admissions. Moderate or severe hyperkalemia (>6.0 mmol/L) affected 12%. Hemolysis affected 2% of all the samples and 24% of hyperkalemic values. On univariate analysis, severity of hypokalemia was associated with mortality (odds ratio 2.2, P = .003).

CONCLUSIONS

Mild potassium abnormalities are common in the PICU. Repeating hemolyzed hyperkalemic samples may be beneficial. Guidance in monitoring frequencies of potassium abnormalities in pediatric critical care is needed.

Errors in potassium measurement: a laboratory perspective for the clinician

Errors in potassium measurement can cause pseudohyperkalemia, where serum potassium is falsely elevated. Usually, these are recognized either by the laboratory or the clinician. However, the same factors that cause pseudohyperkalemia can mask hypokalemia by pushing measured values into the reference interval. These cases require a high-index of suspicion by the clinician as they cannot be easily identified in the laboratory. This article discusses the causes and mechanisms of spuriously elevated potassium, and current recommendations to minimize those factors. "Reverse" pseudohyperkalemia and the role of correction factors are also discussed. Relevant articles were identified by a literature search performed on PubMed using the terms "pseudohyperkalemia," "reverse pseudohyperkalemia," "factitious hyperkalemia," "spurious hyperkalemia," and "masked hypokalemia."

Potassium but not lactate dehydrogenase elevation due to in vitro hemolysis is higher in capillary than in venous blood samples

CONTEXT

Elevated potassium concentrations due to in vitro hemolysis can lead to errors in diagnoses and treatment. Recently, we observed that potassium elevation in capillary samples appeared higher than expected, based on hemolytic index (H-index).

OBJECTIVE

To investigate the relation between potassium increase and H-index for capillary samples. As a control, the same analysis was performed for lactate dehydrogenase (LDH).

DESIGN

Potassium results of 332 760 venous and 2620 capillary samples were selected. For LDH, 135 974 venous and 999 capillary samples were included. Venous and capillary samples were differentiated by using patient age, as we perform mostly capillary blood sampling in children and venous sampling in adults. Results were obtained with Beckman-Coulter DxC800 analyzers.

RESULTS

The increase in potassium with increasing H-index was considerably higher for capillary samples than venous samples. Linear regression revealed a potassium increase of 0.38 mEq/L per increment in H-index for capillary samples, whereas a 0.17 mEq/L increase was found for venous samples. For LDH, no differences were found between venous and capillary samples.

CONCLUSIONS

At identical H-index, capillary samples showed higher potassium elevations than venous samples. A possible explanation is that capillary sampling causes increased leakage of ions, such as potassium, from erythrocytes, compared with proteins such as hemoglobin and LDH. These results are especially important considering the increasing use of whole blood point-of-care analyzers, where the H-index is often not determined. Potassium results should therefore be interpreted with caution to avoid severe misdiagnosis of hypokalemia and hyperkalemia.

A retrospective analysis of the incidence of hemolysis in type and screen specimens from trauma patients

BACKGROUND

Hemolysis of blood samples has been a concern in hospitals. Currently, residents and nurses have replaced traditional teams of skilled phlebotomists for both routine and 'stat' blood draws. Although this leads to a decreased operating cost for institutions, the lack of skill and experience leads to a higher percentage of hemolyzed specimens.

OBJECTIVE

To determine the incidence of hemolyzed 'type and screen' blood samples at Staten Island University Hospital (SIUH) (New York, USA).

METHODS

The study group comprised 615 consecutive trauma patients at SIUH between July 2006 and June 2007. Patients were treated according to the Advanced Trauma Life Support protocol. The primary survey for a trauma patient consists of 'airway', 'breathing' and 'circulation'. The primary objective of 'circulation' is to establish vascular access and collect blood samples for analysis. The SIUH in-house laboratory provided all of the reports.

RESULTS

Of the 615 samples collected, 155 samples (25.2%) were hemolyzed.

CONCLUSIONS

The hemolysis rate of 25.2% for type and screen samples is higher than previously reported in the literature. The data suggest that the high rate of hemolysis in these trauma patients is due to the residents' lack of experience and skills required to obtain an adequate blood draw.

Clinical Biochemistry and Hematology

This chapter discusses the clinical biochemistry and hematology of the rabbit (Oryctolagus cuniculus), guinea pig (Cavia porcellus), hamster (Mesocricetus auratus), and other rodents, including the gerbil (Meriones unguiculatus), chinchilla (Chinchilla laniger), degu (Octodon degus), deer mouse (Peromyscus maniculatus), dormouse (Gliridae family), kangaroo rat (Dipodomys spp.), cotton rat (Sigmodon hispidus), and sand rat (Psammomys obesus). The chapter begins with a review of sample collection and preparation, and a description of commonly measured parameters and analytical techniques. The reference values, sources of variation, and unique characteristics are then presented for each species, as available. Many variables affect the parameters of clinical biochemistry and hematology including methods of sample collection and preparation, equipment, reagents, and methods of analysis, as well as the age, sex, breed, and environment of the animals being sampled. Values obtained from a clinical case are usually compared with reference values that are either produced in the same laboratory or in a similar group of animals, or cited in the literature. Optimal sites for blood collection vary between laboratory animals and are described in this chapter for each species for which information is available. Total blood volume of the rabbit is discussed in the Hematology section of the chapter. The rabbit is recognized as a valuable model for human disturbances in lipid metabolism, such as the metabolic syndrome and hypercholesterolemia leading to atherosclerosis. Hematology is the study of blood and blood-forming organs, including the diagnosis, treatment, and prevention of diseases of the blood, bone marrow, and immunologic, hemostatic, and vascular systems. Hematologic analysis is often used for the diagnosis and treatment of animal diseases.

Pathogenesis, diagnosis and management of hyperkalemia

Hyperkalemia is a potentially life-threatening condition in which serum potassium exceeds 5.5 mmol/l. It can be caused by reduced renal excretion, excessive intake or leakage of potassium from the intracellular space. In addition to acute and chronic renal failure, hypoaldosteronism, and massive tissue breakdown as in rhabdomyolysis, are typical conditions leading to hyperkalemia. Symptoms are non-specific and predominantly related to muscular or cardiac dysfunction. Treatment has to be initiated immediately using different therapeutic strategies to increase potassium shift into the intracellular space or to increase elimination, together with reduction of intake. Knowledge of the physiological mechanisms of potassium handling is essential in understanding the causes of hyperkalemia as well as its treatment. This article reviews the pathomechanisms leading to hyperkalemic states, its symptoms, and different treatment options.

Correction factors for estimating potassium concentrations in samples with in vitro hemolysis: a detriment to patient safety

CONTEXT

Correction factors have been proposed for estimating true potassium concentrations in blood samples with evidence of in vitro hemolysis.

OBJECTIVE

We used 2 different models of true (ie, nonsimulated) in vitro hemolysis to evaluate the clinical utility of correction factors for estimating potassium concentrations in samples with evidence of in vitro hemolysis.

DESIGN

Potassium correction factors were derived using 2 different models. In model 1, potassium and plasma hemoglobin were measured with the Hitachi 747 analyzer in 132 paired blood samples, with each pair consisting of 1 sample with evidence of hemolysis and 1 without, collected during the same phlebotomy procedure. The change in measured potassium concentration was plotted versus the change in plasma hemoglobin concentration for each pair of samples. In model 2, the potassium levels of 142 784 blood samples and the corresponding hemolytic index values were measured with the Beckman LX20 analyzer. Potassium concentrations at the 10th, 25th, 50th, 75th, and 90th percentiles were calculated for each hemolysis index category.

RESULTS

From our 2 models, we derived correction factors expressing an increase in potassium concentration of 0.51 and 0.40 mEq/L for every increase in plasma hemoglobin concentration of 0.1 g/dL. These correction factors are much higher than those reported in studies that simulated in vitro hemolysis by freeze-thaw lysis or osmotic disruption of whole blood.

CONCLUSIONS

Use of correction factors for estimating the true potassium concentration in samples with evidence of in vitro hemolysis is not recommended. Derivation of correction factors by using samples with nonsimulated in vitro hemolysis suggests that the actual increase in potassium in hemolyzed samples is much higher than that reported in previous studies that produced hemolysis with artificial means.

Factitious biochemical measurements resulting from hematologic conditions

Factitious laboratory results often lead to unnecessary testing or treatment. This brief review of factitious biochemical results due to preexisting hematologic conditions focuses on the mechanisms underlying the factitious results and suggests ways to prevent them. An observant pathologist identifies these errors, intervenes in a timely fashion, investigates the sources of error diligently, and institutes measures to prevent their recurrence.

Recommendations for detection and management of unsuitable samples in clinical laboratories

A large body of evidence attests that quality programs developed around the analytical phase of the total testing process would only produce limited improvements, since the large majority of errors encountered in clinical laboratories still prevails within extra-analytical areas of testing, especially in manually intensive preanalytical processes. Most preanalytical errors result from system flaws and insufficient audit of the operators involved in specimen collection and handling responsibilities, leading to an unacceptable number of unsuitable specimens due to misidentification, in vitro hemolysis, clotting, inappropriate volume, wrong container or contamination from infusive routes. Detection and management of unsuitable samples are necessary to overcome this variability. The present document, issued by the Italian Inter-society SIBioC-SIMeL-CISMEL (Society of Clinical Biochemistry and Clinical Molecular Biology-Italian Society of Laboratory Medicine-Italian Committee for Standardization of Hematological and Laboratory Methods) Study Group on Extra-analytical Variability, reviews the major causes of unsuitable specimens in clinical laboratories, providing consensus recommendations for detection and management.

Clin Chem Lab Med 2007;45:728–36.