Azotemia
Reading File
Reading File
Finding Sources
Searching PubMed
azotemia
Searching the Web
azotemia definition causes BUN creatinine Merck Manual
Azotemia is an increase in nitrogen-containing waste products in the blood, mainly urea (measured as BUN) and creatinine, usually because glomerular filtration has fallen. It is a laboratory finding, not a diagnosis itself.
Types and common causes
| Type | Mechanism | Common causes | Typical clues |
|---|---|---|---|
| Prerenal azotemia | Reduced renal perfusion, with structurally intact kidneys | Dehydration, vomiting/diarrhea, hemorrhage, sepsis/shock, heart failure, cirrhosis, NSAIDs, ACE inhibitors/ARBs in susceptible patients | BUN:creatinine often >20:1; urine sodium <20 mmol/L; FENa <1% if not taking diuretics |
| Intrinsic renal azotemia | Damage within the kidney | Acute tubular necrosis, glomerulonephritis, interstitial nephritis, vascular renal disease | Often BUN:creatinine about 10-15:1; urine sediment may be diagnostic, such as muddy brown casts in ATN |
| Postrenal azotemia | Obstruction to urine outflow | Enlarged prostate, stones, tumors, urethral stricture, blocked catheter | Hydronephrosis may be present on ultrasound; relief of obstruction is essential |
Prerenal azotemia results from inadequate renal blood flow without initial parenchymal injury, and can progress to ischemic acute tubular necrosis if prolonged. Robbins, Cotran & Kumar Pathologic Basis of Disease, section “Clinical Manifestations of Renal Diseases.”
Azotemia vs uremia
- Azotemia: elevated BUN/creatinine on blood tests, possibly with no symptoms.
- Uremia: the symptomatic clinical syndrome of advanced renal failure, which may cause nausea, vomiting, pruritus, confusion, pericarditis, seizures, or bleeding tendency.
Evaluation
Assessment usually includes:
- Serum creatinine, BUN, electrolytes, bicarbonate
- Urinalysis and urine microscopy
- Urine output and volume status
- Medication review, especially NSAIDs, ACE inhibitors/ARBs, diuretics, contrast agents, and nephrotoxic drugs
- Renal/bladder ultrasound when obstruction is possible
The BUN:creatinine ratio is only a clue: BUN can rise independently with GI bleeding, high protein intake, corticosteroids, infection, trauma, or increased catabolism, as noted in the Merck renal evaluation guidance.
Urgent assessment is needed if there is very low or absent urine output, dyspnea/pulmonary edema, confusion, severe weakness, chest pain, hyperkalemia, or rapidly rising creatinine.
This is a shared conversation. Sign in to Orris to start your own chat.