Multiple lipoprotein and electrolyte laboratory artifacts caused by lipoprotein X in obstructive biliary cholestasis secondary to pancreatic cancer

Use of therapeutic plasma exchange to remove lipoprotein X in a patient with vanishing bile duct syndrome presenting with cholestasis, pseudohyponatremia, and hypercholesterolemia: A case report and review of literature

INTRODUCTION

Lipoprotein X (Lp-X) is an abnormal lipoprotein found in multiple disease conditions, including liver dysfunction and cholestasis. High Lp-X concentrations can interfere with some laboratory testing that may result in spurious results. The detection of Lp-X can be challenging, and there is currently a lack of consensus regarding the management of Lp-X other than treating the underlying disease.

CASE PRESENTATION

A 42-year-old female with Hodgkin's lymphoma treated with dexamethasone, high dose cytarabine and cisplatin and vanishing bile duct syndrome confirmed by liver biopsy presented with cholestasis, pseudohyponatremia (sodium, 113 mmol/L; reference range 136-146 mmL/L; serum osmolality, 303 mOsm/kg), and hypercholesterolemia (> 2800 mg/dL, reference range < 200 mg/dL). Lp-X was confirmed by lipoprotein electrophoresis (EP). Although she did not manifest any specific signs or symptoms, therapeutic plasma exchange (TPE) was initiated based on laboratory findings of extreme hypercholesterolemia, spuriously abnormal serum sodium, and HDL values, and the potential for short- and long-term sequelae such as hyperviscosity syndrome, xanthoma, and neuropathy. During the hospitalization, she was treated with four 1.0 plasma volume TPE over 6 days using 5% albumin for replacement fluid. After the first TPE, total cholesterol (TC) decreased to 383 mg/dL and sodium was measured at 131 mmol/L. The patient was transitioned into outpatient maintenance TPE to eliminate the potential of Lp-X reappearance while the underlying disease was treated. Serial follow-up laboratory testing with lipoprotein EP showed the disappearance of Lp-X after nine TPEs over a 10-week period.

LITERATURE REVIEW

There are seven and four case reports of Lp-X treated with TPE and lipoprotein apheresis (LA), respectively. While all previous case reports showed a reduction in TC levels, none had monitored the disappearance of Lp-X after completing a course of therapeutic apheresis.

CONCLUSION

Clinicians should have a heightened suspicion for the presence of abnormal Lp-X in patients with cholestasis, hypercholesterolemia, and pseudohyponatremia. Once Lp-X is confirmed by lipoprotein EP, TPE should be initiated to reduce TC level and remove abnormal Lp-X. Most LA techniques are not expected to be beneficial since Lp-X lacks apolipoprotein B. Therefore, we suggest that inpatient course of TPE be performed every other day until serum sodium, TC and HDL levels become normalized. Outpatient maintenance TPE may also be considered to keep Lp-X levels low while the underlying disease is treated. Serum sodium, TC, and HDL levels should be monitored while on maintenance TPE.

A High-Throughput NMR Method for Lipoprotein-X Quantification

Lipoprotein X (LP-X) is an abnormal cholesterol-rich lipoprotein particle that accumulates in patients with cholestatic liver disease and familial lecithin-cholesterol acyltransferase deficiency (FLD). Because there are no high-throughput diagnostic tests for its detection, a proton nuclear magnetic resonance (NMR) spectroscopy-based method was developed for use on a clinical NMR analyzer commonly used for the quantification of lipoproteins and other cardiovascular biomarkers. The LP-X assay was linear from 89 to 1615 mg/dL (cholesterol units) and had a functional sensitivity of 44 mg/dL. The intra-assay coefficient of variation (CV) varied between 1.8 and 11.8%, depending on the value of LP-X, whereas the inter-assay CV varied between 1.5 and 15.4%. The assay showed no interference with bilirubin levels up to 317 mg/dL and was also unaffected by hemolysis for hemoglobin values up to 216 mg/dL. Samples were stable when stored for up to 6 days at 4 °C but were not stable when frozen. In a large general population cohort (n = 277,000), LP-X was detected in only 50 subjects. The majority of LP-X positive cases had liver disease (64%), and in seven cases, had genetic FLD (14%). In summary, we describe a new NMR-based assay for LP-X, which can be readily implemented for routine clinical laboratory testing.

The necessity for improving lipid testing reagents: A real world study

BACKGROUND

We investigated the interference of vitamin C (VitC), glycerol fructose, lipoprotein X (LpX) and lipemia on the analysis of serum lipids.

METHODS

Serum were collected from 44 patients with VitC infusion, serum lipid concentrations before and after VitC auto-oxidation were compared. Serum of 31 patients with glycerol fructose infusion were collected, triglycerides (TG) measured by glycerol blanking and non-blanking reagents were compared. Forty-four serum samples suspected to contain LpX were collected, LDL-C measured by reagents from five manufacturers were compared. Lipemia samples were collected, LDL-C measured using five different reagents were compared. The interference rate was considered unacceptable if it was greater than 1/2 total allowable error (TEa).

RESULTS

In patients with VitC infusion, the interference rates of TG and total cholesterol (TC) were -59% (-123%, -28%) and -15% (-21%, -11%), respectively. In patients with glycerol fructose infusion, the interference rate of TG was 13% (4%, 113%). LpX interference led to increased LDL-C results for most reagents. Lipemia caused great interference with LDL-C analysis.

CONCLUSION

VitC, glycerol fructose, LpX and lipemia significantly interfered with lipid assays. The reagent formulation should be improved to get reliable results.

Spurious Electrolyte and Acid-Base Disorders in the Patient With Cancer: A Review

Electrolyte and acid-base disorders are frequently encountered in patients with malignancy, either due to cancer itself or as a complication of its therapy. However, spurious electrolyte disorders can complicate the interpretation and management of these patients. Several electrolytes can be artifactually increased or decreased such that the serum electrolyte values do not correspond to their actual systemic levels, potentially resulting in extensive diagnostic investigations and therapeutic interventions. Examples of spurious derangements include pseudohyponatremia, pseudohypokalemia, pseudohyperkalemia, pseudohypophosphatemia, pseudohyperphosphatemia, and artifactual acid-base abnormalities. Correctly interpreting these artifactual laboratory abnormalities is imperative for avoiding unnecessary and potentially harmful interventions in cancer patients. The factors influencing these spurious results also must be recognized, along with the steps to minimize them. We present a narrative review of commonly reported pseudo electrolyte disorders and describe strategies to exclude erroneous interpretations of these laboratory values and avoid pitfalls. Awareness and recognition of spurious electrolyte and acid-base disorders can prevent unnecessary and harmful treatments.

Pseudohyponatremia: Mechanism, Diagnosis, Clinical Associations and Management

Pseudohyponatremia remains a problem for clinical laboratories. In this study, we analyzed the mechanisms, diagnosis, clinical consequences, and conditions associated with pseudohyponatremia, and future developments for its elimination. The two methods involved assess the serum sodium concentration ([Na]_S) using sodium ion-specific electrodes: (a) a direct ion-specific electrode (ISE), and (b) an indirect ISE. A direct ISE does not require dilution of a sample prior to its measurement, whereas an indirect ISE needs pre-measurement sample dilution. [Na]_S measurements using an indirect ISE are influenced by abnormal concentrations of serum proteins or lipids. Pseudohyponatremia occurs when the [Na]_S is measured with an indirect ISE and the serum solid content concentrations are elevated, resulting in reciprocal depressions in serum water and [Na]_S values. Pseudonormonatremia or pseudohypernatremia are encountered in hypoproteinemic patients who have a decreased plasma solids content. Three mechanisms are responsible for pseudohyponatremia: (a) a reduction in the [Na]_S due to lower serum water and sodium concentrations, the electrolyte exclusion effect; (b) an increase in the measured sample's water concentration post-dilution to a greater extent when compared to normal serum, lowering the [Na] in this sample; (c) when serum hyperviscosity reduces serum delivery to the device that apportions serum and diluent. Patients with pseudohyponatremia and a normal [Na]_S do not develop water movement across cell membranes and clinical manifestations of hypotonic hyponatremia. Pseudohyponatremia does not require treatment to address the [Na]_S, making any inadvertent correction treatment potentially detrimental.

Interference in Ion-Selective Electrodes Due to Proteins and Lipids

BACKGROUND

Ion-selective electrodes (ISE) have become the mainstay of electrolyte measurements in the clinical laboratory. In most automated analyzers used in large diagnostic laboratories, indirect ISE (iISE) -based electrolyte estimation is done; whereas direct ISE (dISE) -based equipment are mostly used in blood gas analyzers and in the point-of-care (PoC) setting.

CONTENT

Both the techniques, iISE as well as dISE, are scientifically robust; however, the results are often not interchangeable. Discrepancy happens between the two commonly due to interferences that affect the two measuring principles differently. Over the last decade, several studies have reported discrepancies between dISE and iISE arising due to abnormal protein and lipid contents in the sample.

SUMMARY

The present review endeavors to consolidate the knowledge accumulated in relation to interferences due to abnormal protein and lipid contents in sample with the principal focus resting on probable solutions thereof.

Preventing pseudohyponatremia: Intralipid®-based lipemia cutoffs for sodium are inappropriate

BACKGROUND

Pseudohyponatremia describes an artifactual decrease in plasma sodium result in samples with high proteins and/or lipids when measured by an indirect ion-selective electrode (ISE) method. We suspected that Intralipid®-based lipemia cutoffs are inappropriate for detecting interfering lipids in human samples and a major contributing factor to the existence of pseudohyponatremia.

METHODS

We evaluated 2 approaches to derive a lipemia cutoff for sodium, one in which patient plasma samples were pooled and spiked to simulate hyperlipidemia using Intralipid® (commonly used approach by in-vitro diagnostics manufacturers), and another in which endogenous hyperlipidemic samples (n = 31) were measured by methods not affected by hyperlipidemia (i.e., direct ISE and post-ultracentrifugation indirect ISE). Triglycerides, lipemic index (L-index) and indirect ISE sodium concentrations of samples were measured on Roche Cobas® 8000 and direct ISE on Radiometer® ABL835 Flex analyzers. Endogenous hyperlipidemic samples were also ultracentrifuged on Beckman Coulter® Airfuge to clear excess lipids and re-analyzed for sodium by indirect ISE.

RESULTS

We discovered that Intralipid® is not an accurate emulation of the lipemic interference seen in pseudohyponatremia because it showed no effect up to the maximum level of lipemia tested (L-index = 2000). By contrast, endogenous hyperlipidemic samples demonstrated significant deviations in sodium concentration (≥4 mmol/l) when L-index approached or exceeded 700, and a strong positive correlation between L-index and the difference between the indirect and direct methods (i.e., extent of pseudohyponatremia).

CONCLUSIONS

Clinical laboratories should lower their tolerance for lipemia from the currently recommended L-index cutoff of 2000 on Roche Cobas 8000®. We recommend reflexing to direct ISE when L-index exceeds 700. Manufacturers and laboratories with other indirect ISE methods should evaluate the effect of lipid interference on their method using hyperlipidemic human samples not Intralipid®.

Clinical laboratory characteristics of patients with obstructive jaundice accompanied by dyslipidemia

BACKGROUND

Abnormal lipid metabolism manifests as hypercholesterolemia in patients with obstructive jaundice due to lipoprotein X (LpX). Our aim was to explore the clinical laboratory characteristics of patients with obstructive jaundice accompanied by dyslipidemia in a large number of samples.

METHODS

A total of 665 patients with obstructive jaundice were included and categorized into two groups (with/without dyslipidemia) based on the ratio of the sum of HDL-c and LDL-c to total cholesterol [(HDL-c + LDL-c)/TC] with a cut-off value of 0.695. Laboratory liver, kidney, and blood lipid parameters were determined. Cholesterol composition assessment was performed by ultracentrifugation and high-performance liquid chromatography (UC-HPLC), and serum protein profiles were analyzed by capillary electrophoresis.

RESULTS

Liver function in patients with obstructive jaundice accompanied by dyslipidemia was more aggravated than that in patients with simple obstructive jaundice (P < 0.05). The (HDL-c + LDL-c)/TC ratio was negatively correlated with bilirubin levels (P < 0.05). In addition, the difference in ApoB/LDL-c ratios was statistically significant between the obstructive jaundice accompanied by dyslipidemia group and healthy control group (P < 0.05). The LDL-c concentration determined by the UC-HPLC method was more than five times that determined by the enzymatic method (P < 0.05). Bisalbuminemia was found in 43 of 60 patients with obstructive jaundice accompanied by hypercholesterolemia.

CONCLUSIONS

In patients with obstructive jaundice, the decreased (HDL-c + LDL-c)/TC ratio may be a novel marker to identify dyslipidemia secondary to LpX. The decreased ratio was associated with poor liver function and indicated disease progression.

Pseudohyponatraemia caused by acute pancreatitis-derived hypertriglyceridaemia

We report a case of pseudohyponatraemia due to severe hypertriglyceridaemia-induced acute pancreatitis, stemming from unknown diabetes. A woman in her late 30s was admitted to the local hospital by her general practitioner due to severe hyponatraemia (116 mmol/L) and upper abdominal pain. At admission to the hospital, there was a discrepancy of 19 mmol/L between arterial and venous sodium, along with severe hypertriglyceridaemia and hypercholesterolaemia. Pancreatitis was diagnosed using a CT scan. The patient received plasmapheresis which significantly reduced triglycerides, and venous plasma sodium was normalised indicating pseudohyponatraemia at admission. Finally, a haemoglobin A1c of 83 mmol/mol was found. Diabetes was diagnosed, and insulin was initiated.

Detection of Lipoprotein X (LpX): A challenge in patients with severe hypercholesterolaemia

Background

Lipoprotein X (LpX) is an abnormal lipoprotein fraction, which can be detected in patients with severe hypercholesterolaemia and cholestatic liver disease. LpX is composed largely of phospholipid and free cholesterol, with small amounts of triglyceride, cholesteryl ester and protein. There are no widely available methods for direct measurement of LpX in routine laboratory practice. We present the heterogeneity of clinical and laboratory manifestations of the presence of LpX, a phenomenon which hinders LpX detection.

Methods

The study was conducted on a 26-year-old female after liver transplantation (LTx) with severely elevated total cholesterol (TC) of 38 mmol/L and increased cholestatic liver enzymes. TC, free cholesterol (FC), cholesteryl esters (CE), triglycerides, phospholipids, HDL-C, LDL-C, and apolipoproteins AI and B were measured. TC/apoB and FC:CE ratios were calculated. Lipoprotein electrophoresis was performed using a commercially available kit and laboratory-prepared agarose gel.

Results

Commercially available electrophoresis failed to demonstrate the presence of LpX. Laboratory-prepared gel clearly revealed the presence of lipoproteins with γ mobility, characteristic of LpX. The TC/apoB ratio was elevated and the CE level was reduced, confirming the presence of LpX. Regular lipoprotein apheresis was applied as the method of choice in LpX disease and a bridge to reLTx due to chronic liver insufficiency.

Conclusions

The detection of LpX is crucial as it may influence the method of treatment. As routinely available biochemical laboratory tests do not always indicate the presence of LpX, in severe hypercholesterolaemia with cholestasis, any discrepancy between electrophoresis and biochemical tests should raise suspicions of LpX disease.

Plasma lipoprotein-X quantification on filipin-stained gels: monitoring recombinant LCAT treatment ex vivo

Familial LCAT deficiency (FLD) patients accumulate lipoprotein-X (LP-X), an abnormal nephrotoxic lipoprotein enriched in free cholesterol (FC). The low neutral lipid content of LP-X limits the ability to detect it after separation by lipoprotein electrophoresis and staining with Sudan Black or other neutral lipid stains. A sensitive and accurate method for quantitating LP-X would be useful to examine the relationship between plasma LP-X and renal disease progression in FLD patients and could also serve as a biomarker for monitoring recombinant human LCAT (rhLCAT) therapy. Plasma lipoproteins were separated by agarose gel electrophoresis and cathodal migrating bands corresponding to LP-X were quantified after staining with filipin, which fluoresces with FC, but not with neutral lipids. rhLCAT was incubated with FLD plasma and lipoproteins and LP-X changes were analyzed by agarose gel electrophoresis. Filipin detects synthetic LP-X quantitatively (linearity 20-200 mg/dl FC; coefficient of variation <20%) and sensitively (lower limit of quantitation <1 mg/ml FC), enabling LP-X detection in FLD, cholestatic, and even fish-eye disease patients. rhLCAT incubation with FLD plasma ex vivo reduced LP-X dose dependently, generated HDL, and decreased lipoprotein FC content. Filipin staining after agarose gel electrophoresis sensitively detects LP-X in human plasma and accurately quantifies LP-X reduction after rhLCAT incubation ex vivo.

Lp8 is potentially associated with partial lecithin:cholesterol acyltransferase deficiency in a patient with primary biliary cirrhosis

BACKGROUND

The significance of Lp8, that is, abnormal lipoprotein(s) detected in fraction 8 by combined high-performance liquid chromatography/gel filtration column in patients with familial lecithin:cholesterol acyltransferase (LCAT) syndrome, in relation to the severity of LCAT deficiency has not been analyzed.

OBJECTIVE

We have studied Lp8 in a patient with primary biliary cirrhosis.

METHODS

Plasma lipoproteins were analyzed using high-performance liquid chromatography/gel filtration column in the course of treatment of a 47-year-old female patient with primary biliary cirrhosis.

RESULTS

Electrophoretic lipoprotein analyses showed massive accumulation of abnormal ß- and preß-lipoproteins with a minor lipoprotein fraction at a position near the cathode corresponding to Lp-X, on day A (status: hypercholesterolemia, LCAT activity undetectable). Chromatographic lipoprotein subfraction analysis revealed free cholesterol- and phospholipid-rich lipoproteins in fractions 1-6, corresponding to chylomicrons and very low-density lipoprotein, and phospholipid- and triglyceride-rich lipoproteins with increased free cholesterol, that is, Lp8, in fractions 7-9 (corresponding to low-density lipoprotein). On day B, after additional treatment for 7 months (status: almost normolipidemia, decreased LCAT activity), although the abnormal lipoprotein and the lipoproteins in fractions 1-6, were drastically decreased, the presence of Lp8 persisted.

CONCLUSIONS

Lp8 likely is a minor abnormal lipoprotein fraction in patients with mildly decreased secondary LCAT activity, as well as with severely reduced primary LCAT activity.

Pseudohyponatraemia secondary to hyperlipidaemia in obstructive jaundice

A 44-year-old man with uncontrolled diabetes and chronic pancreatitis presented with abdominal pain, jaundice and unintentional weight loss. Laboratory investigations were significant for hyponatraemia, an obstructive pattern of liver enzymes. Imaging was consistent with intrahepatic and extrahepatic biliary obstruction, and endoscopic evaluation revealed a long common bile duct stricture. Intravascular volume depletion, beer potomania and syndrome of inappropriate antidiuretic hormone (with concern for biliary or pancreatic malignancy) were considered in the work-up for the aetiology of the hyponatraemia. After 4 days of conventional treatment, hyponatraemia persisted. Lipid panel obtained revealed very high levels of total cholesterol. The patient underwent a successful biliary diversion and reconstruction surgery. Follow-up after 3 months showed a clinically stable patient with resolution of elevated liver enzymes, hyperlipidaemia and hyponatraemia. We illustrate this rare case of hyponatraemia secondary to hyperlipidaemia in obstructive biliary cholestasis. It is important for physicians to thoroughly investigate the aetiology of hyponatraemia at its onset.

Severe hypercholesterolemia mediated by lipoprotein X in a patient with cholestasis

Lipoprotein X (LpX) is an abnormal lipoprotein associated with cholestasis. It is a significant cause of severe hypercholesterolemia and should always be considered in patients with cholestatic liver disease. This case highlights the significance of LpX as a cause of severe hypercholesterolemia in a patient with cholestasis secondary to a granulomatous hepatitis attributed to tuberculosis. Lipoprotein agarose gel electrophoresis and gradient gel electrophoresis were performed for the detection of LpX. The liver function tests, electrolytes, lipid profile and bile acids were also determined. Anti-tuberculous therapy was initiated and the liver functions improved with normalisation of the lipid profile.

Management of lipoprotein X and its complications in a patient with primary sclerosing cholangitis

Lipoprotein X (LpX) is an abnormal lipoprotein found in conditions such as lecithin:cholesterol acyltransferase deficiency and cholestatic states (e.g., primary biliary cirrhosis and primary sclerosing cholangitis). Management of severe hypercholesterolemia due to LpX with drugs and physical removal methods is not well established in the literature. A case is discussed of a 51-year-old woman who presented with multiple electrolyte abnormalities, xanthomas and neuropathy found to be secondary to LpX in the setting of primary sclerosing cholangitis. This case highlights that oral medications, including statins, may be insufficient to normalize lipid levels or improve clinical symptoms of LpX and presents therapeutic plasma exchange as a safe and effective therapeutic option to treat the morbid sequela of LpX hyperlipidemia.

Extreme hypercholesterolemia presenting with pseudohyponatremia - a case report and review of the literature

Pseudohyponatremia has been reported in association with severe hypertriglyceridemia and hyperparaproteinemia, but its association with severe hypercholesterolemia is not well-known. We report a 43-year-old woman with refractory primary biliary cirrhosis who presented with asymptomatic hyponatremia (121 mmol/L; normal range: 135-145 mmol/L). She was ultimately found to have a total serum cholesterol level of 2415 mg/dL (normal range: 120-199 mg/dL) - secondary to accumulation of lipoprotein-X-causing pseudohyponatremia. The diagnosis was confirmed by measurement of serum osmolality (296 mOsm/kg H2O; normal range: 270-300 mOsm/kg H2O) and serum sodium by direct potentiometry (141 mmol/L). Furthermore, following 16 sessions of plasmapheresis over a 4-month period, there was marked lowering of serum cholesterol to 200 mg/dL and normalization of serum sodium (139 mmol/L) as measured by indirect potentiometry. This case shows that extreme hypercholesterolemia from elevation of lipoprotein-X particles in cholestasis can be a rare cause of pseudohyponatremia. It highlights the need to measure serum sodium with direct potentiometry in the setting of extreme hypercholesterolemia and consider this possibility before initiating treatment of hyponatremia.

Severe Hypercholesterolemia: A Unique Presentation of Non-Hodgkin's Lymphoma in a Patient with Neurofibromatosis Type 1

We report a case of non-Hodgkin's lymphoma (NHL) with an unusual initial manifestation as severe hypercholesterolemia and obstructive jaundice in a patient with neurofibromatosis type 1 (NF 1). NHL should be considered in the evaluation of obstructive jaundice alone or in combination with severe hypercholesterolemia. Relief of biliary obstruction led to the resolution of hypercholesterolemia in our 59-year-old male patient, followed by doxorubicin-based chemotherapy for the underlying lymphoma. NF 1 is a genetic condition that results from a defect in a tumor-suppressor gene and it is likely that this led to the development of NHL in our patient. It is important that clinicians are familiar with the gastrointestinal manifestations of NF 1, especially its association with intra-abdominal malignancies, when treating patients with a personal or family history. To the best of our knowledge, this is the first case of NHL presenting initially as severe hypercholesterolemia and it is also one of the few instances where NHL has been reported in association with NF 1.

Lipoprotein X in a patient with cholestasis and hypertriglyceridaemia

Hypertriglyceridaemia is an established cause of acute pancreatitis and responds to insulin therapy in addition to lipid lowering medication. We report a case of severe hypertriglycaeridemia of 149 mmol/L in a 36–year–old man with type 2 diabetes who presented to the surgical ward with abdominal pain due to pancreatitis and developed acute cholestasis, jaundice and eruptive xanthomata. His triglycerides improved to 3.8 mmol/L with sliding scale insulin within two weeks of in-hospital stay. However, his total cholesterol remained raised at 23.7 mmol/L. The lipoprotein electrophoresis confirmed the presence of lipoprotein X associated with bile obstruction, which contributed to an increase in total cholesterol. The total cholesterol normalized on improvement of his cholestasis.