Mitigating the interference of Daratumumab with immunofixation electrophoresis. A single-center experience using Hydrashift 2/4 kit

BACKGROUND

Multiple myeloma (MM) accounts for approximately 10% of hematological malignancies. The monoclonal immunoglobulin G kappa (IgG-κ) daratumumab can bind to CD38 on MM cells and be detected in serum immunofixation (IF), causing pitfalls in M-protein quantification.

OBJECTIVES

To determine the efficacy of mitigating the interference of IgG MM treated with daratumumab.

METHODS

Levels of Ig, free light chains (FLC) kappa (κ) and lambda (λ), serum protein electrophoresis (SPE)/IF, and Hydrashift 2/4 assays were assessed following manufacturer's instructions in three patients.

RESULTS

Patient 1 was a 70-year-old male diagnosed with IgG-λ MM. The IF distinguished two monoclonal bands (IgG-κ and IgG-λ). With the Hydrashift assay, the daratumumab-anti-daratumumab immune complex shifted the IgG-κ to the α zone, suggesting that the monoclonal IgG-κ band corresponded to daratumumab. Patient 2 was a 63-year-old male with IgG-κ MM who was receiving daratumumab once every other week. SPE/IF assay revealed a faint monoclonal IgG-κ band in the  zone. A stronger monoclonal band was observed after administration. The IgG-κ band disappeared on the Hydrashift assay, while the daratumumab-anti-daratumumab complex appeared as a broad smear in the α-region. Patient 3, a 63-year-old male diagnosed with IgG-λMM, was receiving daratumumab once every other month. The IF assay showed two distinct bands (IgG-κ and IgG-λ) post-daratumumab administration. The shift to the α zone of the IgG-κ bands on the Hydrashift assay confirmed that the additional band observed post-infusion was due to the daratumumab.

CONCLUSIONS

The Hydrashift assay can help distinguish daratumumab from endogenous M-spike.

Urate uptake in membrane vesicles of rat renal cortex: effect of copper

[2-14C]Urate uptake was studied in brush border and basolateral membrane vesicles of rat renal cortex. In the absence of copper, urate equilibrated without metabolism of transported urate. Exposure of the vesicles to copper significantly stimulated uptake, and in these vesicles uptake was also stimulated by NaCl or KCl gradients. Allantoin accumulated in these vesicles due to oxidation of transported urate. This oxidation is ascribed to a copper-stimulated, membrane-associated uricase since purified uricase and the membranes had similar Km values, both were inhibited by oxonic acid, and extramembranal uricase was not detected. Oxonic acid and pyrazinoic acid inhibited both uptake and enzyme activity. These findings suggest that urate uptake is carrier mediated and that uricase may play some role in transport. In addition, it appears that a significant loss of copper occurs during isolation of membrane vesicles that profoundly affects the characteristics of urate uptake. Those properties of the membrane that influence urate uptake, however, can be restored by exposure of the membranes to copper.

Renal CO2 production from glutamine and lactate as a function of arterial perfusion pressure in dog

The energy cost of renal function in the intact kidney of the dog was assessed at a series of arterial perfusion pressures. Pressure was varied by partially inflating a balloon at the tip of a catheter positioned in the aorta above the origins of the renal arteries. Either L-[U-14C]-lactate was infused intravenously in tracer amounts throughout each experiment. Total renal CO2 production and 14CO2 production from each isotope permitted assessment of total renal oxidative metabolism and the proportions derived from the two major substrates of the kidney. Stepwise inflation of the aortic balloon progressively lowered glomerular filtration rate, renal blood inflow, filtered and consequently reabsorbed Na+, total renal CO2 production, and 14CO2 derived from glutamine and lactate. The percent of total CO2 derived from lactate decreased more or less in proportion to the decrease in percent of total CO2 produced. Results were consistent with the view that reabsorption of sodium is the major energy sink of the kidney. They suggest that the oxidation of glutamine supplies energy for tubular transport and basal demands such as synthesis of hormones and maintenance of structure, whereas the oxidation of lactate supplies energy mainly for transport activities.

Renal metabolism of citrate

Our studies on renal handling of citrate have shown that: (1) citrate enters renal tubular cells from luminal fluid (reabsorption) and peritubular blood; (2) reabsorption becomes maximal, i.e., Tm-limited, at filtered loads 7 to 8 times the normal; (3) administration of malate stimulates net renal production of citrate, leading to release into urine (net secretion) and into peritubular blood; (4) acute metabolic alkalosis, induced while plasma citrate levels are above normal, depressess net citrate reabsorption, stimulates citrate release into peritubular blood and abolishes overall renal uptake of citrate; (5) essentially all citrate extracted by the kidney is converted to CO2 at endogenous circulating levels. This contribution is 15 per cent of the total renal CO2 production and is independent of chronic alterations in acid-base balance.