The apDia Ustekinumab ELISA is an enzyme linked immunosorbent assay intended for the quantitative determination of ustekinumab (UST, Stelara®) in human serum and plasma.


Ustekinumab (UST) is a fully human monoclonal antibody that binds to the p40 subunit common to IL-12 and IL-23 thereby preventing the interaction with the cytokine receptors on T cells, natural killer cells and antigen-presenting cells. UST has been approved for treatment of moderate to severe Crohn’s disease (CD), plaque psoriasis and psoriatic arthritis.

A drug can only exerts its pharmacological effect when adequate concentrations are achieved in the circulation. The serum concentration of biologicals just before the next administration, defined as trough concentration, has been used for therapeutic drug monitoring (TDM). Recent data have shown a positive relationship between UST serum concentration, either measured at trough or at an intermediate time point, and clinical outcomes in patients with Crohn’s disease and plaque psoriasis, respectively. TDM may therefore be very instrumental to optimize treatment.

The apDia Ustekinumab ELISA uses highly specific monoclonal antibodies developed at the University of Leuven, Belgium (KU Leuven). Anti-TNF drugs (like infliximab, adalimumab, golimumab) or anti-integrin α4β7 drugs (like vedolizumab) do not interfere with the measurement.

As an example of TDM, the use of UST concentration measurements in plaque psoriasis and CD is described.

Crohn’s Disease

UST is administered intravenously (IV) at week 0 and thereafter every 8 weeks subcutaneously (SC).  The UNITI-1 and -2 induction trials demonstrated that 33.7% and 55.5% of patients had a clinical response at week 6, respectively. During maintenance therapy with SC ustekinumab every 8 weeks, 53.1% of patients were in remission at week 44 in the IM-UNITI trial.

Several studies have demonstrated the relationship between ustekinumab trough concentration and clinical, biological and endoscopic response, indicating the usefulness of therapeutic drug monitoring to guide clinical decision-making.

Plaque psoriasis

UST is weight-based administered subcutaneously at week 0, at week 4 and thereafter every 12 weeks. The Phoenix 1 and 2 trials indicate that treatment with ustekinumab results in rapid, significant improvements in patients with moderate-to-severe psoriasis.

A  recent study demonstrated a concentration-response  relationship  at  week  4  upon  injection  for  ustekinumab-treated psoriasis patients, indicating that monitoring   4-week   post   injection   ustekinumab   concentrations   could   timely   identify underexposed patients who might benefit from treatment optimization.


It has been shown that the immunogenicity of ustekinumab is very low.



The apDia Ustekinumab ELISA uses two highly specific monoclonal antibodies – clones 56C1H12 and 56A2D11, both developed at the KU Leuven – that only detect ustekinumab (Stelara®). 

Microtiterstrips coated with anti-ustekinumab monoclonal antibody clone 56C1H12 are incubated with calibrators, controls and diluted patient samples. During this incubation step ustekinumab binds specifically to the antibodies on the solid phase.  After removal of the unbound serum proteins by a washing procedure, the antigen-antibody complex in each well is detected with specific peroxidase-conjugated anti-ustekinumab monoclonal antibody clone 56A2D11 directed to ustekinumab.
After removal of the unbound conjugate, the strips are incubated with a chromogenic solution containing tetramethylbenzidin and hydrogen peroxide: a blue colour develops in proportion to the amount of immunocomplex bound to the wells of the strips.  The enzymatic reaction is stopped by the addition of 0.5M H2SO4 and the absorbance values at 450 nm are determined.
A standard curve is obtained by plotting the absorbance values versus the corresponding calibrator values. The concentration of ustekinumab in patient samples is determined by interpolation from the calibration curve.