**Core Concept**
The patient presents with symptoms and laboratory findings suggestive of renal involvement in Systemic Lupus Erythematosus (SLE), specifically lupus nephritis, given the presence of hypertension, proteinuria, and an elevated creatinine level. **Lupus nephritis** is a common and serious complication of SLE, often associated with anti-dsDNA antibodies.

**Why the Correct Answer is Right**
Given the acute presentation of hypertension, proteinuria, and a significant rise in creatinine from baseline, along with the absence of RBC casts which might suggest an alternative diagnosis like vasculitis, the most appropriate next step involves managing the potential lupus nephritis flare and the associated hypertension to prevent further renal damage. This typically involves **immunosuppression** and careful management of blood pressure.

**Why Each Wrong Option is Incorrect**
**Option A:** Without specifics, it's hard to judge, but typically, options that do not address the immediate need for immunosuppression and blood pressure management in the context of lupus nephritis would be incorrect.
**Option B:** Similarly, without specifics, if this option does not involve increasing immunosuppression or managing the hypertension and renal involvement, it would be inappropriate.
**Option C:** If this involves only symptomatic treatment without addressing the underlying immunologic issue, it would be insufficient.
**Option D:** If this option suggests a delay in treatment or does not address the acute renal issue and hypertension, it would be incorrect.

**Clinical Pearl / High-Yield Fact**
In patients with SLE, particularly those with a history of high titres of antibodies to dsDNA, any signs of renal dysfunction (such as proteinuria, hematuria, or elevated creatinine) should prompt an urgent evaluation for lupus nephritis. Early initiation of appropriate therapy, including immunosuppressants and careful blood pressure management, is crucial to prevent long-term renal damage.

**Correct Answer:** D. Initiate high-dose corticosteroids and consider adding an immunosuppressive agent.

✓ Correct Answer: C. Initiate high-dose steroid therapy (IV methylprednisolone, 1000 mg daily for 3 doses, followed by oral prednisone, 1 mg/kg daily) and mycophenolate mofetil, 2 g daily.