Felbamate urolithiasis.

Drug-induced nephrolithiasis is an important consideration in recurrent stone formers with polypharmacy. While felbamate nephrolithiasis has previously been published in the paediatric population, we present the oldest published case of a felbamate stone in an adult, a man in his 30s with Lennox-Gastaut syndrome. Even with moderate dosing, high drug serum levels can occur.

LC-MS/MS Method for High-Throughput Analysis of Methylmalonic Acid in Serum, Plasma, and Urine: Method for Analyzing Isomers Without Chromatographic Separation.

Measurement of methylmalonic acid (MMA) plays an important role in the diagnosis of vitamin B deficiency. Vitamin B is an essential cofactor for the enzymatic carbon rearrangement of methylmalonyl-CoA (MMA-CoA) to succinyl-CoA (SA-CoA), and the lack of vitamin B leads to elevated concentrations of MMA. Measurement of MMA in biological samples is complicated because of the presence of succinic acid (SA), isomer of MMA.

Quantification of 5-Hydroxyindoleacetic Acid in Urine by Ultra-performance Liquid Chromatography Tandem Mass Spectrometry.

Serotonin (5-hydroxytryptamine) is a neurotransmitter produced in excess by carcinoid tumors, which develop from enterochromaffin cells. 5-Hydroxyindoleacetic acid (5-HIAA) is the primary urinary metabolite of serotonin, making measurement of 5-HIAA useful in the diagnosis and management of carcinoid tumors. Here we describe a simple, inexpensive, and fast method for the detection and quantification of 5-HIAA in urine.

A Simple, Fast, and Reliable LC-MS/MS Method for the Measurement of Homovanillic Acid and Vanillylmandelic Acid in Urine Specimens.

Homovanillic acid (HVA) and vanillylmandelic acid (VMA) are catecholamine metabolites used in the diagnostic workup of neuroendocrine tumors. Here we describe a simple dilute-and-shoot method for simultaneously quantitating HVA and VMA in human urine specimens. The method employs analyte separation on a reverse-phase liquid chromatography column followed by detection using electrospray ionization triple quadrupole mass spectrometry (ESI-MS/MS), wherein qualifier and quantifier ion transitions are monitored.

A high sensitivity LC-MS/MS method for measurement of 3-methoxytyramine in plasma and associations between 3-methoxytyramine, metanephrines, and dopamine.

Introduction: Diagnosis of pheochromocytoma and paraganglioma (PPGL) is aided by the measurement of metanephrine (MN) and normetanephrine (NMN). Research suggests that 3-methoxytyramine (3MT), a dopamine (DA) metabolite, may serve as a biomarker of metastasis in patients with paraganglioma. Considering the very low endogenous plasma 3MT concentrations (<0.

Professional Certification in Point-of-Care Testing.

Professional certification is affirmation and documentation that the certified individual has the knowledge, training, and skills necessary to practice some aspect of medicine or other profession. Herein is a description of the genesis of a professional certification in point of care testing (POCT), inclusive of rationale and goals. A distinction between professional certification and certificate training programs is made.

Excessively low cholesterol and triglyceride levels in an apparently healthy patient.

Lipid panels are a commonly performed test in clinical laboratories. Due to the high prevalence of cardiovascular diseases around the world, it is common to see serum or plasma specimens with high results for one or more components of the lipid panel. Exceedingly low results, however, are rare and may be attributed to certain genetic, infectious, or autoimmune conditions in addition to analytical interference.

Verifying Clinically Derived Reference Intervals for Daily Excretion Rates of Fractionated Metanephrines Using Modern Indirect Reference Interval Models.

Objectives: Biochemical testing of urinary metanephrines is useful in the diagnosis and monitoring of pheochromocytoma and paragangliomas. We investigated the feasibility of mixture decomposition (ie, indirect) methods in verifying clinically derived reference intervals for urinary deconjugated metanephrine metabolites.

Methods: Urinary 24-hour metanephrine and normetanephrine excretion results were extracted from our data warehouse and intervals were estimated by the modern variant of the Hoffmann method, maximum likelihood estimation (MLE), and gamma mixture model using R software.

Biochemical Diagnosis of Acute Hepatic Porphyria: Updated Expert Recommendations for Primary Care Physicians.

Acute hepatic porphyria (AHP) is a group of rare, metabolic diseases where patients can experience acute neurovisceral attacks, chronic symptoms, and long-term complications. Diagnostic biochemical testing is widely available and effective, but a substantial time from symptom onset to diagnosis often delays treatment and increases morbidity. A panel of laboratory scientists and clinical AHP specialists collaborated to produce recommendations on how to enhance biochemical diagnosis of AHP in the USA.

Development and Clinical Evaluation of a High-Throughput LC-MS/MS Assay for Vitamin B6 in Human Plasma and Serum.

Background: Pyridoxal 5'-phosphate (PLP) is the primary circulatory form of vitamin B6, an essential cofactor for numerous biochemical enzymatic reactions. Conventional PLP analysis using high-performance liquid chromatography (HPLC) with fluorescence requires derivatization and long injection-to-injection time. Development of high-throughput LC-MS/MS assays is desirable.

Thiamine deficiency disorders: diagnosis, prevalence, and a roadmap for global control programs.

Thiamine is an essential micronutrient that plays a key role in energy metabolism. Many populations worldwide may be at risk of clinical or subclinical thiamine deficiencies, due to famine, reliance on staple crops with low thiamine content, or food preparation practices, such as milling grains and washing milled rice. Clinical manifestations of thiamine deficiency are variable; this, along with the lack of a readily accessible and widely agreed upon biomarker of thiamine status, complicates efforts to diagnose thiamine deficiency and assess its global prevalence.

Development and implementation of an HPLC-ECD method for analysis of vitamin C in plasma using single column and automatic alternating dual column regeneration.

Objectives: Vitamin C (l-ascorbic acid) is a water-soluble micronutrient necessary for human life. Inadequate intake can lead to the fatal disease scurvy. Measurement of vitamin C is used to assess nutritional status and to monitor supplementation.

Simple dilute-and-shoot method for urinary vanillylmandelic acid and homovanillic acid by liquid chromatography tandem mass spectrometry.

Background: Neuroblastomas are pediatric tumors characterized by overproduction of catecholamines. The catecholamine metabolites, vanillylmandelic acid (VMA) and homovanillic acid (HVA), are used in clinical evaluation of neuroblastoma. Tandem mass spectrometry (LC-MS/MS) is an effective analytical method for measurement of VMA and HVA in urine.

Practical LC-MS/MS Method for 5-Hydroxyindoleacetic Acid in Urine.

Background: Serotonin, an endogenous biogenic amine found in enterochromaffin cells of the gastrointestinal tract, is produced in excess by carcinoid tumors. The primary urinary metabolite of serotonin, 5-hydroxyindoleacetic acid (5-HIAA), is used in the diagnosis and management of carcinoid disease. This study describes the development and validation of a dilute-and-shoot LC-MS/MS method for the measurement of 5-HIAA in urine.

LC-MS/MS Measurement of Parathyroid Hormone-Related Peptide.

Introduction: Parathyroid hormone-related peptide (PTHrP) is involved in activating pathways, allowing tumor cells to form bone metastases. Measurement of PTHrP is used for the diagnosis and clinical management of patients suspected of hypercalcemia of malignancy. We developed an LC-MS/MS method for measuring PTHrP, established sex-specific reference intervals, and assessed the method's performance.

Thiamine deficiency and cardiac dysfunction in Cambodian infants.

Objectives: To compare blood thiamine concentrations, echocardiography findings, and plasma N-terminal pro-B-type natriuretic peptide (NT-proBNP) levels in infants with clinically diagnosed beriberi and healthy matched controls, and to evaluate changes after thiamine treatment.

Study Design: Sixty-two Cambodian infants (20 cases and 42 controls), aged 2-47 weeks, were enrolled in this prospective study. Echocardiography and phlebotomy were performed at baseline and after thiamine treatment.

Comparison of plasma free metanephrines between healthy dogs and 3 dogs with pheochromocytoma.

Background: Adrenomegaly and hypertension are common clinical entities in canine medicine for which testing for pheochromocytoma is recommended. Yet, a validated biochemical test for the diagnosis of pheochromocytoma in dogs does not exist. In human medicine, plasma free metanephrine testing is the diagnostic standard for the biochemical diagnosis of pheochromocytoma.

Thiamine pharmacokinetics in Cambodian mothers and their breastfed infants.

Background: Thiamine deficiency is common in parts of Asia and causes beriberi. Pharmacokinetics of thiamine in deficient populations are unknown.

Objective: We characterized thiamine pharmacokinetics in Cambodian mothers and their breastfed infants.

Performance characteristics of an LC-MS/MS method for the determination of plasma metanephrines.

Background: Catecholamines and their metabolites, metanephrines, are produced excessively in pheochromocytoma tumors of the chromaffin cells. Increased concentrations of these compounds produce symptoms and allow for clinical evaluation of disease. Historically, screening for such tumors by determination of catecholamines and metabolites in urine yielded false negative results in individuals with a genetic predisposition for the disease and those with paroxysmal hypertension.

Pediatric urinary stone composition in the United States.

Purpose: The incidence of urolithiasis in children is increasing. However, stone composition studies in this population are limited. We sought to determine the effects of age, gender and geographical location on urinary stone composition in the United States pediatric population.

Urinary metanephrines by liquid chromatography tandem mass spectrometry: using multiple quantification methods to minimize interferences in a high throughput method.

Determination of urinary metanephrines is requested frequently for the differential diagnosis and monitoring of pheochromocytoma. Although numerous methods have been developed, interferences are common and hinder most available assays. This study describes the development, validation and implementation of a reliable high-throughput LC-MS/MS method for the measurement of metanephrine and normetanephrine in urine.

Rapid determination of vitamin B₂ (riboflavin) in plasma by HPLC.

Background: Riboflavin (vitamin B₂), as the exclusive source for the coenzymes flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD) in humans, is a water-soluble vitamin critical for metabolism and energy production. In its coenzyme forms, riboflavin is involved in essential oxidation-reduction reactions. Deficiency leads to skin and mucosal disorders.