A 20-year-old woman comes to the office due to gross hematuria. She otherwise feels well and has had no recent illnesses. She had a prior episode of hematuria 2 years ago that resolved spontaneously. The patient was diagnosed with type 1 diabetes mellitus approximately a year ago and is taking daily insulin injections. She works in a day care center and does not use tobacco, alcohol, or illicit drugs. Temperature is 37 C (98.6 F), blood pressure is 120/80 mm Hg, and pulse is 80/min. Physical examination shows no abnormalities. Laboratory results are as follows:
| Serum creatinine | 1.0 mg/dL |
| Serum albumin | 4.0 g/dL |
| Urinalysis | numerous RBCs and few RBC casts; 1+ protein |
| Serum complement | normal |
Which of the following is the most likely diagnosis?
Show Explanatory Sources
This patient has nephritic syndrome (ie, glomerulonephritis), which is characterized by glomerular inflammation, resulting in hematuria and red blood cell casts on urinalysis. Patients may also have mild to moderate proteinuria, although typically less severe than in nephrotic syndrome. Acute kidney injury and hypertension may also be present.
The most common cause of nephritic syndrome is immune complex deposition. Most immune complex–related nephritic syndromes (eg, poststreptococcal or membranoproliferative glomerulonephritis, lupus nephritis) are associated with IgG and/or IgM complexes and have heavy glomerular complement deposition and subsequent serum hypocomplementemia (consumption). However, IgA nephropathy is characterized by normal serum complement levels, as seen in this patient, likely due to the weak complement-fixing activity of IgA compared to that of IgG and IgM.
IgA nephropathy typically presents with gross, often recurrent, hematuria, as in this case. Although this condition classically presents within several days of an upper respiratory infection (synpharyngitic hematuria), a high degree of suspicion must be maintained because episodes may also be spontaneous, as in this patient.
(Choices A, C, and D) Nephrotic syndromes cause heavy proteinuria, resulting in low albumin levels and edema; hematuria and red blood cell casts are typically absent. Etiologies include diabetic nephropathy, membranous nephropathy, and minimal change disease. Diabetic nephropathy typically takes >5 years to develop in type 1 diabetes, although it can be present at the time of diagnosis in patients with type 2 diabetes.
(Choice E) Poststreptococcal glomerulonephritis, which is most common in school-aged children, presents with nephritic syndrome several weeks after infection with group A Streptococcus (eg, pharyngitis, impetigo). This patient has had no recent illnesses, and in contrast to IgA nephropathy, hypocomplementemia would be expected in poststreptococcal glomerulonephritis.
Educational objective:
IgA nephropathy is characterized as recurrent hematuria that occurs spontaneously or within a few days of upper respiratory or pharyngeal infection (synpharyngitic hematuria). Unlike other causes of immune complex–mediated nephritic syndromes (eg, poststreptococcal glomerulonephritis), IgA nephropathy is associated with normal serum complement levels.