Hypercalcemia and elevated concentration of vitamin D: A case report too easy to be true

[A e-Hypercalcemia]

INTRODUCTION

Hypercalcemia is a common biological abnormality. The etiologies are mainly represented by hyperparathyroidism and neoplastic causes. The other causes, including poisoning, are rare, but should not be neglected.

OBSERVATION

An 82-year-old female patient presented to the emergency room for repeated falls at home, confusion, drowsiness and digestive symptoms. The initial assessment showed hypercalcemia above 3mmol/L. The etiological exploration revealed a very high concentration of 25OH-vitamin D. After repeated interrogations, it appeared that the cause of this intoxication was the intake of a food supplement purchased on the internet, following a prescription from her dentist.

CONCLUSION

Intoxication due to a food supplement containing vitamin D is possible and potentially serious. Raising the awareness of patients and healthcare professionals is necessary in order to prevent this type of poisoning and/or to diagnose it as soon as possible.

Pre-analytical mysteries: A case of severe hypervitaminosis D and mild hypercalcaemia

We describe a case of severe hypervitaminosis D and mild hypercalcaemia in a 68-year-old woman who presented with fatigue and weight loss. Her 25-hydroxy vitamin D (25OHD) was > 400 nmol/L (50-150) and corrected serum calcium was 2.83 mmol/L (2.1-2.6). Her intact parathyroid hormone (PTH) was 4.9 pmol/L (2.0-9.5). Further investigation revealed an IgM kappa paraprotein, and a bone marrow aspirate confirmed a diagnosis of lymphoplasmacytic lymphoma/Waldenstrom’s macroglobulinemia (LPL/WM). As the vitamin D level was discordant with the patient’s other results and presentation, the presence of an assay interferent was suspected. A 1-in-2 dilution of the sample returned a 25OHD result of 84 nmol/L in keeping with the presence of an interferent. Testing for rheumatoid factor was negative. The sample was treated with an antibody blocking reagent (Scantibodies) and results were not consistent with heterophile antibody interference. The sample was then analysed using liquid chromatography tandem mass spectrometry (LC-MS/MS), which returned a 25OHD result of 82 nmol/L. Testing on an alternative immunoassay platform produced a 25OHD result of 75 nmol/L. Reapeted testing on the original platform following reduction of the monoclonal paraprotein with chemotherapy, returned a result of 64 nmol/L. The patient’s mild hypercalcaemia persisted following resolution of the monoclonal paraprotein, in keeping with a diagnosis of primary hyperparathyroidism. This case highlights the potential for paraproteins to cause assay interference, and the importance of considering interference when results are incongruous with the clinical presentation.

Falsely markedly elevated 25-hydroxyvitamin D in patients with monoclonal gammopathies

Objectives

Monoclonal immunoglobulins can cause interference in many laboratory analyses. During a 4 month period we observed seven patients with monoclonal disease and falsely extremely elevated 25-hydroxyvitamin D (25(OH)D) results above 160 ng/mL (>400 nmol/L) measured using an immunoassay from Abbott Diagnostics. Based on these findings, we studied the occurrence of falsely elevated 25(OH)D in samples with paraproteins and investigated possible mechanisms of the observed interference.

Methods

25(OH)D was analyzed using the Architect i2000 platform from Abbott Diagnostics and a higher order method, liquid chromatography-mass spectrometry (LC-MS/MS), in serum samples from 50 patients with known monoclonal disease. Patients with falsely elevated 25(OH)D were included in further studies to elucidate the cause of interference. Spuriously elevated results were in addition analyzed on two alternative platforms (Siemens and Roche).

Results

Falsely elevated 25(OH)D levels were present in eight patients on the Abbott analyzer and one on the Siemens platform. Results from Roche were comparable with LC-MS/MS. Additional investigations excluded elevated concentrations of rheumatoid factor and heterophilic antibodies as the cause of interference in the Abbott assay.

Conclusions

Laboratories should be aware of the risk of falsely elevated 25(OH)D in samples run on the Architect analyzer from patients with monoclonal disease. Highly elevated vitamin D results should be diluted and if the dilution is non-linear, rerun by a different method, preferably LC-MS/MS. In patients with spuriously elevated 25(OH)D without known monoclonal disease, the laboratory should consider requesting protein electrophoresis to exclude paraprotein interference.

Falsely Elevated 25-Hydroxy-Vitamin D Levels in Patients with Hypercalcemia

Symptomatic hypercalcemia is a commonly encountered clinical scenario. Though it is important to collect detailed history to find clinical clues connecting to the etiology of hypercalcemia, the diagnostic workup of hypercalcemia depends heavily on laboratory analysis. Accurate measurement of the parathyroid hormone and vitamin D levels is essential. However, commercial laboratory measurement of vitamin D levels can be erroneous in the setting of abundant paraprotein in the serum. One of the most common conditions that can cause an increased amount of paraproteins is multiple myeloma. We report 2 cases of falsely elevated 25-hydroxy-vitamin D levels in patients presenting with hypercalcemia and an underlying diagnosis of MM.

What do you need to know about mass spectrometry? A brief guide for endocrinologists

In routine hormonology, liquid chromatography mass spectrometry (LCMS) is now an established technique for androgen, urinary cortisol and metanephrine assay. It has the undeniable advantage of great analytical specificity, but with sensitivity that clearly depends on financial investment in a very high-end spectrometer. We describe the general principles of LCMS and the routine applications so far developed in hormonology. The purpose is to familiarise endocrinologists with the techniques under development and their pros and cons.

Artefactual 25-OH vitamin D concentration in multiple myeloma

The most commonly used techniques to measure vitamin D are automated immunoassays which are known to be affected by interferences, especially from immunoglobulins present in the patient’s serum. We present a case of a patient with myeloma in whom interference with the vitamin D assay was identified. An 83-year-old female, known to have IgG myeloma, was found to have a high concentration of 25-OH vitamin D on a routine test without any signs of vitamin D toxicity. She was not taking vitamin D supplements or any other multivitamin preparation and had minimal sun exposure. The initial and subsequent samples run by the ARCHITECT 25-OH vitamin D assay (chemiluminescent microparticle immunoassay technology, Abbott Laboratories, Abbott Park, IL) showed a high concentration of 25-OH vitamin D of 281 nmol/L and 327 nmol/L, respectively. Further fresh samples taken for 25-OH vitamin D and analysed by liquid chromatography-mass spectrometry (LC-MS/MS) and ARCHITECT analysis showed results of 49 nmol/L and 289 nmol/L, respectively. Our patient had high concentrations of circulating IgG paraproteins and had a long history of rheumatoid arthritis; paraproteins and rheumatoid factor may interfere in the assay. In conclusion, we report a case of a patient with IgG myeloma and rheumatoid arthritis with high concentrations of 25-OH vitamin D detected by the Abbott ARCHITECT, but not by a reference method (LC-MS/MS). The most likely cause of the discordant results is interference in the immunoassay by the paraprotein but interference from rheumatoid factor remains a possibility.