Vitamin D Assays in Paraproteinemias: A Case Report

Presentation Number: MON 359
Date of Presentation: April 3rd, 2017

Kenechukwu Mezue*1, Kimberly Kochersperger Lessard1, Napatt Kanjanahattakij2 and Patamaporn Lekprasert3
1Albert Einstein Medical Center, Philadelphia, PA, 2Internal Medicine, Albert Einstein Medical Center, Philadelphia, PA, 3Einstein Medical Center, Philadelphia, PA

Abstract

Background: Proper assessment of vitamin D levels in patients with paraproteinemias poses challenges in interpretation and mandates understanding of various testing modalities.

Case: A 63-year-old female with a history of schizophrenia and recently diagnosed IgG lambda multiple myeloma with extensive osseous metastasis presented to the emergency room with back pain, abdominal pain, generalized weakness, and anorexia over one month. On presentation she was hemodynamically stable and physical exam was remarkable only for dry mucosal membranes and diffuse paraspinal tenderness to palpation. Laboratory studies revealed Hgb 7 mg/dL(12-16mg/dL), MCV 91.2 fL (81-96 fL), sodium 126 mEq/L (136-146 mEq/L), potassium 3.7 mEq/L (3.6-5.1 mEq/L), chloride 92 mEq/L (98-107 mEq/L), bicarbonate 27 mEq/L (22-31 mEq/L), blood urea nitrogen 35 mg/dL (9-21 mg/dL), creatinine 3.1 mEq/L (0.7-1.2 mEq/L) and calcium of 16.6 corrected 18.3 mg/dL (8.4 -10.3 mg/dL), albumin level of 2.1 mg/dL (3.5-5 mg/dL) and globulin level of 8.9 mg/dL (2.1 -3.7 mg/dL). Hypercalcemia was treated with intravenous fluids, calcitonin and zoledronic acid, after which it trended downwards to normal within 72 hours. The initial 25-OH Vitamin D level resulted at > 96 ng/mL by radioimmunoassay (RIA) (30 - 50 ng/mL) which was above the analytical range of the analyzer. PTH level was 8.0 pg/mL (9-73 pg/mL). With no history of high dose vitamin D supplement use and with consideration for the possibility of interference of myeloma antibodies with RAI assay, reanalysis of 25-OH Vitamin D levels of the initial sample was performed using liquid chromatography/mass spectrometry (LCMS) method. This revealed a total 25-OH Vitamin D level within normal range at 46 ng/mL (normal 30 - 100 ng/mL) and total 1,25-Dihydroxy Vitamin D level of 12 pg/mL (18 - 72 pg/mL).

Discussion: Hypercalcemia, as discovered in this patient, was secondary to known multiple myeloma. However, the initial Vitamin D level obtained using RAI, the most commonly utilized method, was markedly high. Obtaining accurate levels of Vitamin D is a critical component in management, as true Vitamin D intoxication would require high dose corticosteroids rather than calcium-stabilizing therapy. Reanalysis using the liquid chromatography/mass spectrometry method revealed that Vitamin D levels were normal in the patient. This tells us that the Vitamin D levels obtained by the RAI method were misleadingly high; this is possibly due to interference by endogenous antibodies generated by the abnormal plasma cells in multiple myeloma as suggested in similar cases existing in the literature. This case reminds us that other non-radioimmune assays should be used in the evaluation of patients with paraproteinemias such as multiple myeloma to ensure an accurate result.

 

Nothing to Disclose: KM, KKL, NK, PL