Studies on thrombocytosis. I. Hyperkalemia due to release of potassium from platelets during coagulation

Stability of potassium, calcium and phosphorus electrolytes in three different tubes in patients with essential thrombocytosis

Proper blood collection and timely analysis are vital steps for reliable results. This study aims to compare potassium(K), calcium(Ca), and phosphorus(P) concentrations in serum separator tube (SST), lithium heparin tube without gel (LiH), and lithium heparin tube with a barrier (Barricor)tubes in essential thrombocytosis(ET) patients. Additionally, we assessed short-term stability of these analytes at room temperature. K, Ca and P concentrations of blood taken from 40 ET patients into SST, LiH and Barricor tubes were measured at 0, 2, 4 and 8 h. We calculated the percentage difference and defined the maximum permissible difference (MPD) using the Biological Variation Database. Intertube comparisons were conducted using Passing-Bablok regression and Bland-Altman analysis. Comparing SST to LiH, the percentage difference values for all tests exceeded the MPD. When comparing Barricor to LiH, K and Ca tests were above MPD, except for P. At the 8th hour, LiH showed clinically significant changes in all three electrolytes. Barricor exhibited stability for K, Ca, and P for up to 8 h, with only Ca levels borderline higher than the MPD. Our study reveals clinically significant alterations in K, Ca, and P concentrations in SST compared to LiH tubes, and in K and Ca concentrations in Barricor compared to LiH tubes. While K, Ca and P concentrations were stable for up to 4 h at room temperature in all tube types tested, significant changes were observed in all electrolytes at 8 h in the LiH tube.

Pseudohyperkalemia in chronic lymphocytic leukemia: Prevalence, impact, and management challenges

The term pseudohyperkalemia refers to a false elevation in serum potassium levels due to potassium release from cells in vitro. Falsely elevated potassium levels have been reported in patients with thrombocytosis, leukocytosis, and hematologic malignancies. This phenomenon has been particularly described in chronic lymphocytic leukemia (CLL). Leukocyte fragility, extremely high leukocyte counts, mechanical stress, higher cell membrane permeability related to an interaction with lithium heparin in plasma blood samples, and metabolite depletion due to a high leukocyte burden have been reported to contribute to pseudohyperkalemia in CLL. The prevalence of pseudohyperkalemia is up to 40%, particularly in the presence of a high leukocyte count (>50 × 109/L). The diagnosis of pseudohyperkalemia is often overlooked, which may result in unnecessary and potentially harmful treatment. The use of whole blood testing and point-of-care blood gas analysis, along with thorough clinical evaluation, may help differentiate between true and pseudohyperkalemic episodes.

Characterizing ability of serum potassium (K) and the serum K reference interval to flag hypokalemia or hyperkalemia as observed in plasma: a simulation study

OBJECTIVES

Serum potassium (K) exhibits a positive shift relative to plasma K due to a variable amount of K release associated with clotting. Because of this variation, plasma K results outside of the reference interval (RI) for plasma (hypokalemia or hyperkalemia) in individual samples may not produce classification-concordant results in serum according to the serum RI. We examined this premise from a theoretical standpoint by simulation.

DESIGN & METHODS

We used textbook K reference intervals for plasma (PRI = 3.4-4.5 mmol/L) and serum (SRI = 3.5-5.1 mmol/L). The difference between PRI and SRI is characterized by a normal distribution: serum K = plasma K + 0.35 ± 0.308 mmol/L. This transformation was applied by simulation to an observed patient data distribution for plasma K to generate a corresponding theoretical serum K distribution. Individual samples were tracked for comparison with respect to classification (below, within, above RI) for plasma and serum.

RESULTS

Primary data were an all-comers plasma K patient distribution (n = 41,768; median = 4.1 mmol/L; 7.1% below PRI (hypokalemia); 15.5% above PRI (hyperkalemia)). Simulation to obtain the associated serum K yielded a right-shifted distribution (median = 4.4 mmol/L; 4.8% below SRI; 10.8% above SRI). Sensitivity for detection in serum (flagged below SRI) for samples originating as hypokalemic in plasma was 45.7% (specificity = 98.3%). Sensitivity for detection in serum (flagged above SRI) for samples originating as hyperkalemic in plasma was 56.6% (specificity = 97.6%).

CONCLUSIONS

Simulation results indicate that serum K should best be thought of as an inferior substitute marker for plasma K. These results follow simply from the variable component of serum K compared to plasma K. Plasma should be the preferred specimen type for K assessment.

Accuracy and stability evaluation of different blood sampling methods in blood gas analysis in emergency patients: A retrospective study

BACKGROUND

To evaluate the accuracy and stability of arterial blood gas (ABG) results by comparison with venous measurements from routine blood tests, and to compare the accuracy and performance of two sampling syringes, pre-heparinized syringe (PHS) and disposable arterial blood syringe (DABS), in ABG analysis.

METHODS

We retrospectively analyzed the practical use of PHS and DABS in collecting ABG samples, involving 500 and 400 patients, respectively. For each patient, in addition to the ABG sample, a venous blood sample was also collected using a venous blood collection tube (VBCT) and used for routine blood tests. Accordingly, patients were referred to as the PHS + VBCT group and DABS + VBCT group. The correlation between arterial and venous values of each blood parameter in each group was evaluated using the interclass correlation coefficient (ICC). Bland-Altman was performed to evaluate the agreement between arterial and venous values and compare the performance of PHS and DABS in ABG sample collection.

RESULTS

In the PHS + VBCT group, arterial K⁺ , Na⁺ , hemoglobin (Hb), and hematocrit (HCT) were 0.32 mmol/L, 2.90 mmol/L, 2.21 g/L, and 1.27% significantly lower their corresponding venous values while arterial Cl^- was 7.60 mmol/L significantly higher than venous Cl^- . In the DABS + VBCT group, arterial K⁺ and Na⁺ were 0.20 mmol/L and 1.19 mmol/L significantly lower while Cl^- and HCT in arterial blood were 5.34 mmol/L and 0.66% significantly higher than their corresponding venous values. In both groups, arterial K⁺ , Na⁺ , Hb, and HCT values were highly consistent with their corresponding venous values, with all ICCs greater than 0.70, especially Hb and HCT. Bland-Altman analysis demonstrated that arterial K⁺ and Na⁺ were more consistent with venous counterparts in the DABS + VBCT group, with a narrower 95% limits of agreement than the PHS + VBCT group (K⁺ , -0.7-0.3 mmol/L vs. -1.1 to 0.5 mmol/L; Na⁺ , -5.8 to 3.4 mmol/L vs. -8.2 to 2.4 mmol/L).

CONCLUSION

Arterial blood gas analysis of K⁺ , Na⁺ , Hb, and HCT using PHS or DABS for blood sampling is accurate and stable, especially DABS, which can provide clinicians with fast and reliable blood gas results.

Clinical Thresholds for Pseudohyperkalemia and Pseudonormokalemia in Patients with Thrombocytosis

BACKGROUND

The lysis of platelets during in vitro coagulation leads to increased potassium concentrations.We aimed to establish the cut-off value for platelet count interfering serum potassium and to estimate the percentage of cases of pseudohyperkalemia and pseudonormokalemia in our hospital.

MATERIALS AND METHODS

Individuals diagnosed with essential thrombocytosis (2010-2019) based on the WHO criteria for the classification of myeloid neoplasms and acute leukemia were considered.The cut-off value for the interference of platelet count on serum potassium results was calculated using the reference change value. Sensitivity and specificity were calculated using a ROC-curve, and the size of the effect by the Cohen's d.The clinical impact of both phenomena was assessed by reviewing the medical records of individuals classified as such, and also looking for potential cases in 2019 on the laboratory information system.

RESULTS

Fifty-four individuals with essential thrombocytosis were included. Potassium concentration correlated with platelet count (P-value<0.001; Spearman's ρ =0.394) in serum. The cut-off value of platelet count interfering potassium was 598x10³/μL [CI95%: 533-662x10³/μL], with an associated sensitivity and specificity of 0.67 [CI95%:0.52-0.80] and 0.58 [CI95%:0.42-0.72] respectively.The medical records of patients classified as pseudohyperkalemia or pseudonormokalemia did not include any medical action for the modification of potassium levels. In 2019, up to 0.14% of the total serum potassium determinations were susceptible to be pseudohyperkalemia or pseudonormokalemia.

CONCLUSION

This study provides a cut-off value for platelet count interfering serum potassium concentrations, and brings to light not only pseudohyperkalemia-related issues, but also the pseudonormokalemia phenomenon, which usually goes unnoticed.

Reverse pseudohyperkalemia in a newly diagnosed pediatric patient with acute T-cell leukemia and hyperleukocytosis: a case report and literature review

Background

Hyperkalemia is a serious medical condition that requires immediate intervention. However, pseudohyperkalemia and reverse pseudohyperkalemia are misleading clinical manifestations that can result in incorrect diagnosis and consequent harmful intervention.

Case presentation

An 11-year-old girl manifested an incidental finding of hyperleukocytosis (WBC > 400 × 109/L), with 90% blast cells during routine pre-operative investigations for adenotonsillectomy. Initial investigations demonstrated elevated serum potassium levels (7.5 mmol/L), despite concomitantly normal levels in venous blood gas samples (3.9–4.4 mmol/L) and being clinically stable with normal 12-lead ECG. Surprisingly, plasma potassium level was exacerbated, in comparison to the serum level by > 1 mmol/L. This finding is consistent with reverse pseudohyperkalemia that is associated with hyperleukocytosis in acute leukemia that does not require any active intervention.

Conclusion

This case report emphasizes the significance of interpreting potassium levels accurately, preferably utilizing whole-blood potassium level over serum and plasma level in newly diagnosed leukemia cases with hyperleukocytosis. Additionally, having a high index for the possibility of reverse pseudohyperkalemia, secondary to leakage from fragile leukocytes, avoids unnecessary treatment that might cause harm to the patient.

Effects of handling and storage on potassium concentration in plasma and serum samples obtained from cats

OBJECTIVE

To compare potassium concentrations in feline plasma and serum samples analyzed promptly after collection or after 20 to 28 hours of refrigerated storage.

ANIMALS

41 cats.

PROCEDURES

A venous blood sample was obtained from each cat. Aliquots were placed in 2 tubes without anticoagulant (blood was allowed to clot to derive serum) and 2 tubes with heparin (to derive plasma). One serum and 1 plasma sample were kept at room temperature and analyzed within 60 minutes after collection (baseline); the other serum and plasma samples were analyzed after 20 to 28 hours of refrigerated storage. At both time points, serum and plasma potassium concentrations were measured.

RESULTS

Median baseline serum potassium concentration (4.3 mmol/L) was significantly higher than median baseline plasma potassium concentration (4.1 mmol/L). The median difference between those values was 0.4 mmol/L (95% CI, 0.2 to 0.5 mmol/L). Compared with their respective baseline measurements, the median serum plasma concentration (4.8 mmol/L) and median plasma potassium concentration (4.6 mmol/L) were higher after 20 to 28 hours of refrigeration.

CLINICAL RELEVANCE

Results indicated that with regard to potassium concentration in feline blood samples, clotting or refrigerated storage for 20 to 28 hours results in a significant artifactual increase. Detection of an unexpectedly high potassium concentration in a cat may represent pseudohyperkalemia, especially if the blood sample was placed in a no-additive tube, was stored for 20 to 28 hours prior to analysis, or both.

Reverse pseudohyperkalemia is more than leukocytosis: a retrospective study

BACKGROUND

Hyperkalemia is a potentially life-threatening electrolyte abnormality that often requires urgent treatment. Clinicians should distinguish true hyperkalemia from pseudohyperkalemia and reverse pseudohyperkalemia (RPK). RPK has exclusively been described in case reports of patients with hematologic malignancies (HMs) and extreme leukocytosis [white blood cell (WBC) count >200 × 103/mL].

METHODS

This single-center retrospective study analyzed laboratory data from the Mount Sinai Data Warehouse between 1 January 2010 and 31 December 2016 for plasma potassium and serum potassium samples drawn within 1 h of each other, with plasma potassium ≥1 mEq/L of the serum potassium. Only plasma potassium ≥5 mEq/L were included. Samples that were documented to be hemolyzed or contaminated were excluded. Clinical history and laboratory data were collected from the identified cases.

RESULTS

After applying the inclusion/exclusion criteria to 485 potential cases, the final cohort included 45 cases from 41 patients. There were 24 men and 17 women with a mean age of 52 years. The median plasma potassium was 6.1 mEq/L and serum potassium was 4.4 mEq/L. The median WBC count was 9.35 × 103/mL (interquartile range 6.5-19.7 × 103/mL). Only 44% of the samples had leukocytosis, defined as WBC >11 × 103/mL.Seven patients had a HM and comprised 11 of the cases (24%) with a median WBC of 181.8 × 103µL. There was no difference in their plasma and serum potassium levels when compared with the total cohort, despite a higher median WBC count. Thirty-eight percent of the cases required medical management.

CONCLUSIONS

The literature on RPK is limited to case reports and series associated with extreme leukocytosis. This is the first study characterizing RPK predominantly associated with normal leukocyte counts. Further investigation is required to more precisely characterize factors associated with RPK and to elucidate RPK mechanisms.

Pseudohyperkalemia and Pseudohyponatremia in Two Children with T-Cell Acute Lymphoblastic Leukemia

Pseudohyperkalemia and pseudohyponatremia are phenomena in which hematologic disorders with high cell counts result in factitious electrolyte measurements that can result in inappropriate treatment. We describe 2 children with leukemia presenting with both disturbances to highlight the importance of correlating electrolyte results from plasma with those from whole blood before intervening.

[Pseudohyperkalemia and thrombocytosis]

INTRODUCTION

Hyperkalemia is common in medicine and requires rapid management. Besides the easily evoked causes such as renal failure, adrenal insufficiency, cell lysis or iatrogenic causes, false or pseudo-hyperkalemia should not be forgotten.

OBSERVATIONS

Three patients (1 man, 2 women, aged 78, 84, 88) were managed for thrombocytosis (between 1306 and 2404 G/L) and non-symptomatic hyperkalemia (between 6.1 and 7.7mmol/L) are reported. Kalemia on blood collected in heparin tube was normal (4.4-4.6mmol/L). Therefore, no specific treatment for this pseudohyperkalemia was required.

CONCLUSION

The combination of thrombocytosis and non-symptomatic hyperkalemia should suggest the diagnosis of pseudohyperkalemia and should prompt for a control of kalemia on blood collected in heparin tube. The recognition of this diagnosis is important in order to avoid unnecessary and potentially deleterious treatment of hyperkalemia.

Accuracy of Hemolyzed Potassium Levels in the Emergency Department

Introduction

In the emergency department (ED), pseudohyperkalemia from hemolysis may indirectly harm patients by exposing them to increased length of stay, cost, and repeat blood draws. The need to repeat hemolyzed potassium specimens in low-risk patients has not been well studied. Our objective was to determine the rate of true hyperkalemia among low-risk, adult ED patients with hemolyzed potassium specimens.

Methods

We conducted this prospective observational study at two large (129,000 annual visits) academic EDs in the mid-Atlantic. Data were collected from June 2017–November 2017 as baseline data for planned departmental quality improvement and again from June 2018–November 2018. Inclusion criteria were an initial basic metabolic panel in the ED with a hemolyzed potassium level > 5.1 milliequivalents per liter that was repeated within 12 hours, age (≥18, and bicarbonate (HCO₃) > 20. Exclusion criteria were age > 65, glomerular filtration rate (GFR) < 60, creatine phosphokinase > 500, hematologic malignancy, taking potassium-sparing or angiotensin-acting agents, or treatment with potassium-lowering agents (albuterol, insulin, HCO₃, sodium polystyrene sulfonate, or potassium-excreting diuretic) prior to the repeat lab draw.

Results

Of 399 encounters with a hemolyzed, elevated potassium level in patients with GFR ≥ 60 and age > 18 that were repeated, we excluded 333 patients for age > 64, lab repeat > 12 hours, invalid identifiers, potassium-elevating or lowering medicines or hematologic malignancies.This left 66 encounters for review. There were no instances of hyperkalemia on the repeated, non-hemolyzed potassium levels, correlating to a true positive rate of 0% (95% confidence interval 0–6%). Median patient age was 46 (interquartile range [IQR] 34 – 56) years. Median hemolyzed potassium level was 5.8 (IQR 5.6 – 6.15) millimoles per liter (mmol/L), and median repeated potassium level was 3.9 (IQR 3.6 – 4.3) mmol/L. Median time between lab draws was 145 (IQR 87 – 262) minutes.

Conclusion

Of 66 patients who met our criteria, all had repeat non-hemolyzed potassiums within normal limits. The median of 145 minutes between lab draws suggests an opportunity to decrease the length of stay for these patients. Our results suggest that in adult patients < 65 with normal renal function, no hematologic malignancy, and not on a potassium-elevating medication, there is little to no risk of true hyperkalemia. Further studies should be done with a larger patient population and multicenter trials.

The potential role of the eGFR in differentiating between true and pseudohyperkalaemia

BACKGROUND

Differentiating between true and pseudohyperkalaemia is essential for patient management. The common causes of pseudohyperkalaemia include haemolysis, blood cell dyscrasias and EDTA contamination. One approach to differentiate between them is by checking the renal function, as it is believed that true hyperkalaemia is rare with normal function. This is logical, but there is limited published evidence to support it. The aim of this study was to investigate the potential role of the estimated glomerular filtration rate in differentiating true from pseudohyperkalaemia.

METHODS

GP serum potassium results >6.0 mmol/L from 1 January 2017 to 31 December 2017, with a repeat within seven days, were included. Entries were retrospectively classified as true or pseudohyperkalaemia based on the potassium reference change value and reference interval. If the initial sample had a full blood count, it was classified as normal/abnormal to remove blood cell dyscrasias. Different estimated glomerular filtration rate cut-points were used to determine the potential in differentiating true from pseudohyperkalaemia.

RESULTS

A total of 272 patients were included with potassium results >6.0 mmol/L, with 145 classified as pseudohyperkalaemia. At an estimated glomerular filtration rate of 90 ml/min/1.73 m², the negative predictive value was 81% (95% CI: 67-90%); this increased to 86% (95% CI: 66-95%) by removing patients with abnormal full blood counts. When only patients with an initial potassium ≥6.5 mmol/L were included (regardless of full blood count), at an estimated glomerular filtration rate of 90 ml/min/1.73 m², the negative predictive value was 100%. Lower negative predictive values were seen with decreasing estimated glomerular filtration rate cut-points.

CONCLUSION

Normal renal function was not associated with true hyperkalaemia, making the estimated glomerular filtration rate a useful tool in predicting true from pseudohyperkalaemia, especially for potassium results ≥6.5 mmol/L.

Reverse pseudohyperkalemia and pseudohyponatremia in a patient with B-cell non-Hodgkin lymphoma

OBJECTIVES

Investigate concomitant and spurious high potassium and low sodium results in heparinized plasma.

METHODS

Potassium and sodium values were measured from heparinized plasma and serum in a patient with B-cell non-Hodgkin lymphoma using both an automated chemistry analyzer (indirect ion selective electrode) and blood gas analyzer (direct ion selective electrode).

RESULTS

Potassium levels were significantly increased while sodium levels were significantly decreased in heparinized plasma compared to serum on several occasions.

CONCLUSIONS

To our knowledge, concomitant reverse pseudohyperkalemia and pseudohyponatremia has not been reported previously. We postulate the discrepancy between plasma and serum sodium (pseudohyponatremia in plasma) may be unique to cases of reverse pseudohyperkalemia with extreme potassium elevations.

Pseudohyperkalemia: Look before you treat

Pseudohyperkalemia is defined as a reported rise in serum potassium concentration along with a normal effective plasma potassium concentration. We present a case report of a 57-year-old gentleman with a history of chronic lymphocytic leukemia, who presented with an elevation in serum potassium along with a normal plasma potassium concentration. Through an exploration of the literature, we demonstrate that pseudohyperkalemia is an important phenomenon to watch for as it may sometimes lead to unnecessary and potentially dangerous treatment.

Reversible iatrogenic paraparesis secondary to masked hypokalaemia in thrombocytosis-associated pseudohyperkalaemia

An elderly patient who presented with recent recurrent falls was admitted, reporting inability to stand and recent acute diarrhoeal illness. Paraparesis was diagnosed but extensive investigations did not elucidate its cause. He had atherosclerotic cardiac and vascular disease, diabetes, hypertension, chronic kidney disease and pancreatectomy/splenectomy for a lesion that turned out to be benign. He was receiving multiple medications including kayexalate, which was started a few weeks prior, and the dose increased, due to hyperkalaemia up to 6.3 mEq/L. Although the postsplenectomy thrombocytosis was not striking (700×10⁹/L), spurious hyperkalaemia (pseudohyperkalaemia) was suspected when no cause of hyperkalaemia could be identified and widely fluctuating serum potassium levels were noted. Concurrent K⁺ determination in the serum and plasma revealed that the patient actually had significant masked hypokalaemia (2.4 mEq/L). Once kayexalate was stopped and normokalaemia (in plasma) achieved by replacement therapy, paraparesis completely resolved (5/5 muscle strength) and no more falls occurred after discharge.

Pseudohyperkalemia in a Patient with T-Cell Acute Lymphoblastic Leukemia and Hyperleukocytosis

A 7-year-old girl presented with lymphadenopathy and bruising suggestive of leukemia. Complete blood count was significant for white blood cell count of 479,000/mm ³ . Basic metabolic panel sent via pneumatic tube system was significant for potassium > 10 mEq/L. The stat venous blood gas potassium level was 4.6 mEq/L. A 12-lead-ECG showed sinus tachycardia without peaked T-waves. It was determined that this was pseudohyperkalemia associated with significant hyperleukocytosis. This brief report discusses rare causes of pseudohyperkalemia that can be overlooked, and details the postulated mechanisms for pseudohyperkalemia in the setting of hyperleukocytosis.

Establishing evidence-based thresholds and laboratory practices to reduce inappropriate treatment of pseudohyperkalemia

BACKGROUND

Unrecognized pseudohyperkalemia (PHK), defined as an artificial increase in measured potassium concentration, due to thrombocytosis and leukocytosis can lead to inappropriate patient treatment. Understanding the laboratory and patient characteristics that increase risk of PHK is key to preventing diagnostic errors.

METHODS

Serum/plasma potassium results collected at 2 laboratories over 4years were selected based on blood cell counts collected within 24h and whole blood potassium concentrations determined within 2h of the serum/plasma sample. Differences between whole blood and serum or plasma potassium were compared as functions of platelet or leukocyte count, fit to linear models, and stratified based on leukemia diagnosis codes. Patients having a serum/plasma potassium concentration that was at least 1mEq/mL higher than the whole blood concentration were defined as having PHK. Based on this analysis, high-risk patients were prospectively identified and PHK risk was communicated to providers. Medication administration records were queried to compare rates of kayexalate use pre- and post-intervention.

RESULTS

Approximately 14% of serum samples with platelet counts >500×10⁹/L had a>1mEq/L increase relative to whole blood potassium. >25% of serum and plasma samples showed a>1mEq/L increase relative to whole blood potassium when leukocyte counts were >50×10⁹/L. Patients with chronic lymphocytic leukemia and high WBC count demonstrated the highest rates of PHK. The rate of kayexalate administration prior to confirmatory testing decreased from 37% to 16% after the laboratory started verbally communicating the possibility of PHK to treating providers.

CONCLUSIONS

According to our data, a leukocyte count threshold for plasma samples of 50×10⁹/L is appropriate for indicating a high risk of PHK. Direct communication by the laboratory to the care team reduces inappropriate potassium lowering treatment in populations at high risk.

Pseudohyperkalaemia: a rare complication of splenectomy

Pseudohyperkalaemia is an uncommon and frequently unrecognised biochemical abnormality. It occurs as a consequence of aggregation and lysis of platelets in vitro. As a result, potassium is released, which causes an elevated serum concentration. We present the case of a 21-year-old man with a traumatic splenic injury necessitating laparotomy and splenectomy. Following surgery he developed hyperkalaemia. Further investigations diagnosed pseudohyperkalaemia, one of the causes of which is thrombocytosis secondary to splenectomy.

Pre-Analytical Parameters Affecting Vascular Endothelial Growth Factor Measurement in Plasma: Identifying Confounders

Background

Vascular endothelial growth factor-A (VEGF-A) is intensively investigated in various medical fields. However, comparing VEGF-A measurements is difficult because sample acquisition and pre-analytic procedures differ between studies. We therefore investigated which variables act as confounders of VEGF-A measurements.

Methods

Following a standardized protocol, blood was taken at three clinical sites from six healthy participants (one male and one female participant at each center) twice one week apart. The following pre-analytical parameters were varied in order to analyze their impact on VEGF-A measurements: analyzing center, anticoagulant (EDTA vs. PECT / CTAD), cannula (butterfly vs. neonatal), type of centrifuge (swing-out vs. fixed-angle), time before and after centrifugation, filling level (completely filled vs. half-filled tubes) and analyzing method (ELISA vs. multiplex bead array). Additionally, intrapersonal variations over time and sex differences were explored. Statistical analysis was performed using a linear regression model.

Results

The following parameters were identified as statistically significant independent confounders of VEGF-A measurements: analyzing center, anticoagulant, centrifuge, analyzing method and sex of the proband. The following parameters were no significant confounders in our data set: intrapersonal variation over one week, cannula, time before and after centrifugation and filling level of collection tubes.

Conclusion

VEGF-A measurement results can be affected significantly by the identified pre-analytical parameters. We recommend the use of CTAD anticoagulant, a standardized type of centrifuge and one central laboratory using the same analyzing method for all samples.

Postsplenectomy thrombocytosis with pseudohyperkalaemia

A 52-year old man developed hyperkalaemia on the 11th postoperative day following an extensive open retroperitoneal liposarcoma resection that included splenectomy. Despite thorough investigations, no aetiology for the hyperkalaemia was identified and standard empirical treatment was ineffective. On reconsideration, in view of the patient's concurrent thrombocytosis, a pseudofactual or artefactual hyperkalaemia was suspected. This was confirmed by contemporaneous testing of serum and plasma potassium levels, with the latter value lying within the normal range. Treatment for hyperkalaemia was discontinued, thus averting an iatrogenic and potentially dangerous hypokalaemia. This case highlights pseudohyperkalaemia as an often-neglected cause of elevated serum potassium levels and discusses its association with thrombocytosis following splenectomy.

Pseudohyperkalaemia is a common finding in myeloproliferative disorders that may lead to inappropriate management of patients

Pseudohyperkalaemia in conditions with increased platelet counts is caused by an in vitro rise of the serum potassium concentration during whole blood coagulation and the lysis of the platelets and other cellular components, in the presence of normal renal function and normal plasma potassium levels. The association between pseudohyperkalaemia and aetiology of thrombocytosis was studied in a 6-year retrospective audit on 90 patients with thrombocytosis referred to the Haematology Department in Ulster Hospital Dundonald, a large district general hospital. Over two-thirds of this study population had myeloproliferative disorders, and the most common diagnosis was primary thrombocythaemia (41%, n = 37). Reactive thrombocytosis was observed in approximately one-third of the cases (32%, n = 29). Pseudohyperkalaemia with apparent potassium level above the upper limit of the normal range (reference range K 3.5-5.1 mmol/l) was observed in the majority of patients with thrombocytosis from any aetiology (60%, n = 54). The likelihood of finding pseudohyperkalaemia was highest among patients with primary thrombocythaemia (75.7%, n = 28/37) and polythaemia rubra vera (75%, n = 12/16), followed by myelofibrosis (50%, 4/8) and reactive thrombocytosis (34.5%, n = 10/29). A highly significant positive correlation was observed between the platelet counts and the serum potassium level (Spearman's correlation coefficient, R = 0.998, P = 0.01). Awareness of pseudohyperkalemia in disease conditions with increased platelet counts will lead to the withholding of potentially harmful treatment.

Pseudohyperkalemia in serum: a new insight into an old phenomenon

Pseudohyperkalemia, a rise in serum potassium concentration with concurrently normal plasma potassium concentration, is an in vitro phenomenon that was first described 50 years ago. It was originally attributed to the release of potassium from platelets during platelet aggregation and degranulation, and a significant correlation between pseudohyperkalemia and platelet count was established. During the last decade, new data were added to this phenomenon. In particular, pseudohyperkalemia was defined when serum potassium concentration exceeded that of plasma by more than 0.4 mmol/L provided that samples are collected under strict techniques, remain at room temperature and are tested within 1 hour from blood specimen collection. Moreover, it is positively correlated to (1) thrombocytosis due to the release of potassium from platelet granules during coagulation, (2) erythrocytosis due to the dilution of the released potassium in smaller volumes of serum, and (3) the presence of activated platelets, which have the capability of aggregation at a higher speed and release more potassium during degranulation. However, pseudohyperkalemia may be "masked" when in a state of hypokalemia because potassium moves back into the intracellular space in vitro, and the phenomenon is ameliorated or even not detected.

Pseudohyperkalemia in serum: the phenomenon and its clinical magnitude

We investigated in detail the difference between serum and plasma potassium levels in patients with several conditions associated with pseudohyperkalemia. In total, 435 patients with either thrombocytoses, erythrocytoses, leucocytoses, or a mixed-type disorder and 30 healthy controls were included. In each case, the index Dk [serum potassium minus plasma potassium] and the index Dk100 (Dk x 100,000/platelets), which indicates the Dk value that corresponds to platelets of 100,000/mm(3), were estimated. Median Dk was significantly higher in the groups with platelet, erythrocyte, or mixed-type disorders than in the controls (P=0.001). Among these groups, Dk values were significantly higher in patients with thrombocytosis or mixed-type disorders compared with those with erythrocytosis (P<0.001, for both). Furthermore, no significant difference was observed in Dk values between controls and patients with white blood cell disorders (P=0.74). Dk values did not exceed 2.61 mmol/L, whereas Dk100 values were inversely related to platelet counts (r=-0.351, P<0.01). In conclusion, pseudohyperkalemia is mainly present in patients with thrombocytosis or mixed-type disorders, probably as a result of the degranulation of platelets, which offers a potassium load to the surrounding plasma at the time of clot formation in vitro. However, the degree of pseudohyperkalemia does not increase proportionally with the increase of platelet counts, which may be associated with transfer of part of potassium load from the plasma back into red and white blood cells.

Pseudohyperkalemia in Patients with Increased Cellular Components of Blood

OBJECTIVE

We performed a study to investigate the difference between serum and plasma potassium concentration in patients with increase in one or more of the cellular components of blood.

DESIGN AND METHODS

This study was performed in two phases. During the first phase, we performed a cross-sectional comparison of the difference between serum and plasma potassium concentration (Dk) in 341 patients with the various clinical conditions where pseudohyperkalemia has been described, as well as with secondary or spurious erythrocytosis and in 30 normal controls. A cut-off value of Dk discriminating polycythemia vera from other erythrocytoses was estimated. In the second phase we studied the significance of this cut-off value as predictor of polycythemia vera in 90 naive patients who were referred with an elevated hematocrit.

RESULTS

Dk was significantly increased in the groups with platelet, erythrocyte or with a mixed type disorder compared to the controls (P < 0.01). Among these groups, Dk was significantly increased in the groups with thrombocytosis and mixed type disorder, compared to the group with erythrocytosis (both P < 0.01). A cut-off value of Dk discriminating polycythemia vera from other erythrocytoses was estimated (0.70 mmol/L). Dk (> or = 0.70 mmol/L), platelet and white blood cell count were identified as significant independent predictors of polycythemia vera.

CONCLUSIONS

The Dk is increased in patients with erythrocytoses, thrombocytoses or both. This phenomenon is more profound in patients with a mixed type disorder, such as polycythemia vera patients, compared to those with erythrocytoses alone.

Pseudohyperkalemia Due to Pneumatic Tube Transport in a Leukemic Patient

Pseudohyperkalemia is an elevation in measured serum or plasma potassium levels caused by mechanical release of potassium from cells during phlebotomy or specimen processing. We describe a case of pseudohyperkalemia caused by mechanical disruption of white blood cells from a leukemic patient because of pneumatic tube transport of the specimen. This is the first description of pneumatic tube transport causing pseudohyperkalemia, and clinicians should be aware of this potential cause of false elevation of plasma potassium levels.

Hematology and clinical chemistry values of normal and euthymic hairless adult male Dunkin-Hartley guinea pigs (Cavia porcellus)

Hematology and serum chemistry measurements were performed on blood specimens from 12 male Dunkin-Hartley hairless guinea pigs Crl:IAF(HA)BR and 10 haired Dunkin-Hartley male guinea pigs Crl:(HA)BR. Significantly higher activities of alanine aminotransferase, aspartate aminotransferase, amylase, and creatine kinase were observed in the hairless guinea pigs as compared to the haired strain. Alkaline phosphatase activity was found to be lower in the hairless guinea pig. The hairless guinea pigs were found to have serum urea concentrations approximately 46% higher than the normal guinea pig strain. The erythrocytic mean cell volume of the hairless strain was found to be smaller, with a greater hemoglobin content. Hairless guinea pigs were found to have approximately 40% fewer leukocytes with a reversed lymphocyte:neutrophil ratio compared to the haired guinea pigs which had much higher lymphocyte counts.

Fluid and electrolyte abnormalities

Patients with cancer are at risk for developing a variety of fluid and electrolyte disturbances caused by the disease process or by complications from therapy. An understanding of the pathophysiology of these potential abnormalities allows the clinician to manage patients expectantly and to avoid severe metabolic disarray by correcting imbalances promptly.

Artefactual serum hyperkalaemia and hypercalcaemia in essential thrombocythaemia

AIM

To investigate possible abnormalities of serum potassium and calcium levels in patients with essential thrombocythaemia and significant thrombocytosis.

METHODS

24 cases of essential thrombocythaemia with significant thrombocytosis (platelet count > 700 x 10(9)/litre) had serum potassium and calcium estimations performed at the time of maximum thrombocytosis before treatment, and at the time of low platelet count after treatment with cytoreductive drugs. Selected patients were further investigated with plasma sampling and estimation of ionised calcium and parathyroid hormone.

RESULTS

At the time of maximum thrombocytosis six patients had serum hyperkalaemia (> 5.5 mmol/litre) and five had serum hypercalcaemia (> 2.6 mmol/litre). Following treatment and reduction of the platelet count, hyperkalaemia resolved in all cases and hypercalcaemia in four of the five cases. Mean serum potassium and calcium concentrations were raised (p < 0.0001) at maximum thrombocytosis compared with the values when the platelet count was low. Serum potassium and calcium values were significantly correlated at all stages. Measurements on plasma consistently corrected the hyperkalaemia but not the hypercalcaemia. Serum hypercalcaemia was associated with raised ionised calcium and normal parathyroid hormone concentrations.

CONCLUSIONS

Essential thrombocythaemia with significant thrombocytosis is associated with serum hyperkalaemia and hypercalcaemia. The probable mechanism of hypercalcaemia is the secretion of calcium in vitro from an excessive number of abnormally activated platelets. It is thus likely that the hypercalcaemia is an artefact, as is the hyperkalaemia.

SPURIOUS HYPERKALAEMIA

In a patient with acute lymphoblastic leukaemia, the plasma was found to have a potassium level of 10.4 mEq./1. Investigations showed that plasma from patients with leukaemia may be found to have falsely high potassium levels because of breakdown of leucocytes between the venepuncture and separation of the plasma.

Hypercalcemia and electrolyte disturbances in malignancy

Hypercalcemia and electrolyte abnormalities are common problems in patients with malignancy. In this article we discuss the pathophysiology, clinical features, and management of hypercalcemia, which is the most common metabolic abnormality. We also analyze the electrolyte disturbances that occur in association with malignancy, including hyponatremia, hypokalemia, hypomagnesemia, hypophosphatemia, and hyperkalemia. Recognition and treatment of these disturbances are important parts of the management of patients with malignant disease.

Effect of platelet count on serum and plasma potassium: evaluation using database information from two hospitals

The availability of retrospective data from potassium (K+) analyses from two hospitals, one using serum and the other plasma for electrolyte measurements, offered us the possibility to investigate the effect of blood platelet count on serum and plasma K+ concentrations. A weak correlation between plasma K+ and platelet count was observed. The in vitro increase of serum K+ in proportion to the platelet count has clinical significance in conditions, where it may impede the detection of an underlying true K+ disorder. Nomograms and correction factors, based on the correlation between platelet count and serum K+, have been suggested also in some recent reports. In the present study unselected routine patient data was used as source data. The effect of platelet count on the concentration of K+ in serum was lower than reported in previous studies, as indicated by the regression analysis. An increase of 1000 x 10(9)/l in the blood platelet count would cause an increase of about 0.7 mmol/l in the serum K+ concentration (p < 0.0001, r = 0.155). The weak correlation between platelet count and serum K+ does not support the application of platelet-count-based correction of serum K+ level in thrombocytosis. The laboratory should notify the clinician of the significance of the in vitro increase of K+ caused by increased platelet count. K+ should be measured from plasma in such cases.

Pseudohyperkalaemia in Kawasaki disease

Pseudohyperkalaemia was observed in 3 of 16 patients with Kawasaki disease showing remarkably increased platelet counts. Their plasma potassium concentration, which is not affected by in vitro coagulation, was in the normal range despite the increased serum level. A significant correlation was observed between the platelet count and the increase in the serum potassium level resulting from blood coagulation, which was estimated by subtracting the plasma potassium level from the serum level. This study indicates that pseudohyperkalaemia should be considered in patients with Kawasaki disease whose platelet counts are markedly increased.