The patient in this vignette most likely has acute post-streptococcal glomerulonephritis (PSGN). The next step in the management of any patient with suspected renal pathology should be urinalysis.
Urinalysis (UA) is a cheap, fast, and informative test. Classically, a UA detects urine leukocytes, nitrites, urobiliniogen, protein, pH, blood, specific gravity, ketones, bilirubin, and glucose. In this case of PSGN, we would expect to see increased RBCs, WBCs +/- elevated protein.
Rahman et al. discuss acute kidney injury (AKI), which is characterized by an abrupt deterioration in kidney function. The best surrogate marker of renal function is an increase in serum creatinine level. AKI may or may not result in reduced urine output. Workup of suspected AKI should involve a physical examination to assess intravascular volume status and identify skin rashes indicative of systemic illness. Initial tests should include serum creatinine level, complete blood count, urinalysis, and fractional excretion of sodium.
Meister et al. performed a meta-analysis of four studies (pooled n = 948) involving the diagnosis of UTIs in females. They conclude that there is no single H&P finding that can accurately rule in or rule out UTI in symptomatic women, but a urinalysis with a positive nitrite or moderate pyuria and/or bacteruria is an accurate predictor. For clinical decision-making, if the pretest probability of UTI is sufficiently low, a negative urinalysis can accurately rule it out.
Illustration A is an example of a urinalysis, with the ranges and parameters tested.
Answer 2: ASO titers would be most likely elevated in this patient with suspected PSGN, but would not be the best initial test.
Answer 3: There is no role for renal US in this immediate context.
Answer 4: There is no role for abdominal CT in this immediate context.
Answer 5: There is no role for antibiotics in the treatment of PSGN.
Rahman M, Shad F, Smith MC. Acute kidney injury: a guide to diagnosis and management. Am Fam Physician. 2012 Oct 1;86(7):631-9.
PMID:23062091 (Link to Abstract)
Meister L, Morley EJ, Scheer D, Sinert R. History and physical examination plus laboratory testing for the diagnosis of adult female urinary tract infection. Acad Emerg Med. 2013 Jul;20(7):631-45.
PMID:23859578 (Link to Abstract)