A 22-year-old man comes to the clinic complaining of dark urine that he noticed earlier this morning. He is recovering from an upper respiratory tract infection that started 6 days ago. The patient's temperature is 98.9 F, blood pressure is 145/92 mm Hg, pulse is 80/min, and respirations are 14/min. Physical examination shows no skin rash and no joint abnormalities. Laboratory results are as follows

Urinalysis:

• Glucose - Negative
• Protein- 1+
• Ketones- Negative
• Leukocyte esterase- Negative
• Nitrites- Negative
• White blood cells- 3-6/hpf
• Red blood cells- 30-50/hpf
• Casts- Red blood cells

Serum Chemistry:

• Serum sodium- 138 mEq/L
• Serum potassium- 4.5 mEq/L
• Bicarbonate- 22 mEq/L
• Blood urea nitrogen- 18 mg/dL
• Serum Creatinine- 1.4 mg/dl
• Serum C3 and C4- normal

Other serological workup is pending

Questions:
1. What is your most likely diagnosis, and state the clues that helped you make your diagnosis?
2. What would your findings be on Electron Microscopy from Kidney Biopsy?
3. How would you manage the case?
4. What would your diagnosis be if the patient had skin rash and joint pain?