A 75-year-old man is brought to the emergency department from a skilled nursing facility due to lethargy and decreased oral intake for the past 3 days. He has had multiple episodes of watery diarrhea. His blood pressure is 90/60 mm Hg, and his heart rate is 112/min. Physical examination reveals dry mucous membranes and poor skin turgor. Laboratory studies are obtained:
| Test | Result | Reference Range |
|---|---|---|
| Sodium | 140 mEq/L | 136-145 mEq/L |
| Potassium | 3.8 mEq/L | 3.5-5.0 mEq/L |
| Chloride | 104 mEq/L | 98-106 mEq/L |
| Bicarbonate | 24 mEq/L | 22-28 mEq/L |
| Blood urea nitrogen (BUN) | 54 mg/dL | 8-20 mg/dL |
| Creatinine | 1.8 mg/dL | 0.7-1.3 mg/dL |
| Urine sodium | 12 mEq/L | Varies with diet |
| Urine osmolality | 680 mOsm/kg HO | 50-1200 mOsm/kg HO |
Urinalysis reveals a specific gravity of 1.028, no protein, no blood, and rare hyaline casts. His baseline serum creatinine from one month ago was 0.9 mg/dL. Based on these laboratory findings, which of the following is the most likely diagnosis?
- Prerenal azotemiaCevap
- BAcute tubular necrosis
- CAcute interstitial nephritis
- DAcute glomerulonephritis
- EObstructive uropathy
Cevap
Prerenal azotemia
The correct answer is prerenal azotemia. The patient has a clear history of fluid loss (diarrhea) leading to hypovolemia, supported by hypotension and tachycardia. The laboratory results confirm this with a characteristic prerenal pattern: a BUN-to-creatinine ratio of 30:1 (normal is approximately 10-15:1; > 20:1 indicates a prerenal state), a low urine sodium (< 20 mEq/L), and a highly concentrated urine (osmolality > 500 mOsm/kg H2O and specific gravity > 1.020). The urinalysis is bland, featuring only rare hyaline casts, which are concentrated Tamm-Horsfall proteins frequently seen in concentrated urine and not indicative of intrinsic disease.
Adım Adım Çözüm
Anahtar Kavram
The classic laboratory profile of prerenal azotemia includes a BUN-to-creatinine ratio greater than 20:1, urine sodium less than 20 mEq/L, fractional excretion of sodium (FENa) less than 1%, and a highly concentrated urine (osmolality > 500 mOsm/kg H2O, specific gravity > 1.020) with a bland sediment.