Chemistry, toxicology & urinalysis

Endogenous	Exogenous
Fibrinogen Hemolysis Antianimal antibodies Polyclonal increases in IgG4: monoclonal gammopathy mimicry	Contrast dyes Antifungals and antibiotics Gelatin based plasma substitutes Hydroxocobalamin Monoclonal antibody therapies

• Reference: Clin Biochem 2018;51:72

Drugs	Peak zones on CZE
5 fluorocytosine (5FC)	Cathodal region of γ globulin fraction
Ceftriaxone	Anodal region of the prealbumin fraction
Sulfamethoxazole	Albumin peak
Piperacillin with tazobactam	α2 β1 globulin region

• These interferences are more likely to occur when blood samples are collected closer to the time of perfusion, especially in the context of renal failure and drug accumulation
• Reflex testing to IFE or immunotyping can confirm the absence of a monoclonal component
• See image 3
• Reference: Clin Biochem 2018;51:72

• Many of the available monoclonal therapeutics can appear as monoclonal IgG kappa by IFE
• Of the monoclonal drugs used for non-plasma cell dyscrasia based diseases, only rituximab and bevacizumab in therapeutic doses produced a visible M protein on SPEP / IFE
• Drugs like siltuximab, daratumumab and elotuzumab (all IgG kappa monoclonal antibodies) can appear as a small M protein, most often in concentrations of no more than 1 g/L or 0.1 g/dL, when used in therapeutic doses (Clin Chem 2010;56:1897)
• The main concern with the presence of these therapies is misclassification of disease response as having a very good partial response (VGPR) as opposed to a complete response
• Practically applicable mitigation response to monoclonal therapy varies with subtype of clonal immunoglobulin produced by plasma cell neoplasm

IgG plasma cell neoplasm

Plasma cell neoplasm other than IgG

When starting therapy, laboratory might not be able to separate therapeutic monoclonal bands and should report the detection and quantification of the M protein as standard with the additional information that the quantification might be influenced by interference from the therapeutic drug When evaluating treatment response close to complete response (M protein < 2 g/L), laboratory can add a specific assay, e.g., the daratumumab specific immunofixation electrophoresis reflex assay (DIRA), to mitigate the potential comigration of the therapeutic drug with the malignant M protein Another option that laboratories can use is to ask for a report from pharmacy indicating each instance when a patient receives monoclonal therapy susceptible to interfere with IFE

When starting therapy, laboratory should report the detection of the malignant M protein as standard with the supplementary information of a second M spike / M band at the expected electrophoretic position of the therapeutic drug Therapeutic M protein should also be quantified at initial recognition and should under normal circumstances not exceed 1 g/L As malignant M protein and the known therapeutic M protein are of different Ig subtype, the evaluation of treatment response should not be hindered by the phenomenon of comigration of the M proteins

• Daratumumab specific immunofixation electrophoresis reflex assay (DIRA) using an antibody targeting daratumumab to alter the migration of daratumumab during electrophoresis should be utilized
• Reference: Clin Biochem 2018;51:72

Contributed by Ahsan Farooq, M.D. and Yusheng Zhu, Ph.D.

Which of the following statements regarding electrophoreses after initiation of monoclonal therapy is true?

1. Electrophoresis studies should be done before administration of monoclonal antibodies
2. Immunofixation electrophoresis (IFE) will show a peak in the anodal part of the γ region with daratumumab
3. Short time interval between serum protein electrophoresis (SPEP) and drug administration should decrease chances of interference
4. SPEP showing a peak of 300 mg/dL will always mean a very good partial response (VGPR)

A. Electrophoresis studies should be done before administration of monoclonal antibodies. Before each dose, the concentration of therapeutic monoclonal will be lowest and thus give less interference. Answer C is incorrect because with longer intervals between the dose and testing, interference will be less. Answer B is incorrect because daratumumab usually migrates to the cathodal part of the γ region. Answer D is incorrect because a value of < 1 g/dL can be due to therapeutic monoclonal therapy.

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Reference: Interference in protein electrophoresis

Serum electrophoresis of a 60 year old man identifies a peak. Immunofixation electrophoresis (IFE) is performed. Which most the following is most consistent with the findings?

1. Patient has multiple myeloma
2. Plasma sample of patient with macrocytic anemia
3. Serum sample obtained immediately after monoclonal therapy
4. Serum sample of patient with IgG related disease

B. Plasma sample of patient with macrocytic anemia. Plasma contains fibrinogen; plasma sample was erogenously run instead of serum. Answer C is incorrect because IFE shows no monoclonal antibody. Answer D is incorrect because the band is in β / γ region. Answer A is incorrect because IFE shows no monoclonal antibody.

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Reference: Interference in protein electrophoresis