### Date : 2024-11-24 13:27 ### Topic : Azotemia #nephrology ---- ### **Azotemia** **Azotemia** is a condition characterized by an **elevation in nitrogenous waste products** (mainly **blood urea nitrogen (BUN)** and **creatinine**) in the blood. These waste products are typically excreted by the kidneys. When kidney function is impaired, **azotemia** occurs, reflecting the inability of the kidneys to effectively filter and eliminate these substances. ### **신장 기능 검사 (Renal Function Tests)** | 항목 | 정상 범위 | 단위 | |--------------------|--------------------|-------------| | **Blood Urea Nitrogen (BUN)** | 8–20 | mg/dL | | **Creatinine (Cr)** | 남성: 0.7–1.3 <br> 여성: 0.6–1.1 | mg/dL | | **Glomerular Filtration Rate (GFR)** | >90 | mL/min/1.73m² | ### **Causes of Azotemia**: Azotemia can be classified into three types based on its origin: 1. **Prerenal Azotemia**: - **Cause**: Results from conditions that lead to a **reduction in blood flow to the kidneys**, causing impaired filtration of blood and accumulation of nitrogenous waste products. - **Mechanisms**: Decreased perfusion (blood flow) to the kidneys leads to reduced glomerular filtration rate (GFR). This can be caused by: - **Hypovolemia**: Dehydration, blood loss, or excessive fluid loss (e.g., vomiting, diarrhea, sweating). - **Heart failure**: Reduced cardiac output leads to decreased renal perfusion. - **Shock**: Septic, hypovolemic, or cardiogenic shock reduces renal blood flow. - **Renal artery stenosis**: Narrowing of the renal arteries reduces blood flow to the kidneys. - **Key Findings**: - **Elevated BUN and creatinine** levels. - **Urinary sodium** is usually low (because the kidneys try to retain sodium to conserve fluid). - **FENa (fractional excretion of sodium)** is typically less than 1%. 2. **Renal (Intrarenal) Azotemia**: - **Cause**: This occurs when there is **direct damage to the kidney tissue**, including the glomeruli, tubules, or blood vessels, impairing their ability to filter waste. - **Mechanisms**: Damage to the kidneys reduces their ability to excrete nitrogenous waste products. Conditions causing intrarenal azotemia include: - **Acute tubular necrosis (ATN)**: Often caused by ischemia (due to prolonged hypoperfusion) or nephrotoxic substances (e.g., certain medications like **NSAIDs**, **aminoglycosides**, or contrast agents). - **Glomerulonephritis**: Inflammation of the glomeruli, often caused by **autoimmune diseases** (e.g., **lupus**, **post-streptococcal glomerulonephritis**). - **Acute interstitial nephritis (AIN)**: Inflammation of the kidney interstitium, commonly due to drugs, infections, or systemic diseases. - **Key Findings**: - Elevated **BUN** and **creatinine** levels. - **Urinary sodium** is usually **high** (indicating the kidneys are unable to properly reabsorb sodium). - **FENa > 2%**: Suggests tubular dysfunction. - **Urine sediment** may show **casts** (e.g., **muddy brown casts** in ATN, **red blood cell casts** in glomerulonephritis). 3. **Postrenal Azotemia**: - **Cause**: Occurs due to **obstruction of urine outflow** anywhere in the urinary tract (from the kidneys to the bladder). The obstruction leads to backflow of urine, increased pressure in the kidneys, and impaired filtration. - **Mechanisms**: Any condition that blocks the outflow of urine can lead to postrenal azotemia. These include: - **Kidney stones**: Obstruction of the renal pelvis or ureters. - **Bladder outlet obstruction**: Prostate enlargement (benign prostatic hyperplasia or BPH), bladder cancer, or neurological disorders affecting bladder function. - **Ureteral obstruction**: Due to tumors, fibrosis, or stones. - **Key Findings**: - **Elevated BUN and creatinine**. - **Urinary sodium** is usually low, but **FENa** can be low or normal. - **Urine output** may be reduced, or there may be signs of **post-void residual urine** if the bladder is obstructed. - **Imaging** (e.g., ultrasound, CT scan) may reveal **hydronephrosis** (swelling of the kidney due to urine backup). --- ### **Symptoms of Azotemia**: - **Fatigue** and **weakness** due to the buildup of waste products. - **Nausea** and **vomiting**, which are often related to uremia (a more severe form of azotemia). - **Loss of appetite**. - **Shortness of breath** due to fluid overload. - **Confusion** or **altered mental status**, especially in **uremic encephalopathy**. - **Edema**: Fluid retention caused by kidney dysfunction can lead to swelling in the legs, face, and abdomen. --- ### **Diagnosis of Azotemia**: 1. **Blood Tests**: - **Serum creatinine** and **BUN**: Both elevated in azotemia, but **creatinine** is a more reliable indicator of renal function. - **Electrolyte abnormalities**: May show **hyperkalemia**, **hyponatremia**, and **metabolic acidosis** in severe cases. 2. **Urinalysis**: - **Urinary sodium**: Helps distinguish between prerenal (low sodium) and renal causes (high sodium). - **FENa**: Fractional excretion of sodium helps differentiate prerenal from intrinsic renal causes. A value of less than 1% suggests prerenal azotemia. - **Urine sediment**: Can show **casts** in intrinsic renal causes like ATN or glomerulonephritis. 3. **Imaging**: - **Ultrasound** or **CT scan**: Used to check for postrenal causes (e.g., hydronephrosis, stones, or tumors). 4. **Renal Biopsy**: - May be necessary in cases of **intrarenal azotemia** to determine the exact cause, particularly in conditions like glomerulonephritis or interstitial nephritis. --- ### **Treatment of Azotemia**: 1. **Prerenal Azotemia**: - **Fluid resuscitation**: Restore blood volume with IV fluids (e.g., saline or Ringer's lactate) to improve renal perfusion. - **Treat underlying cause**: Manage heart failure, blood loss, dehydration, or shock. 2. **Renal Azotemia**: - **Dialysis** may be needed in cases of severe kidney dysfunction, especially in acute tubular necrosis (ATN) or glomerulonephritis. - **Treat underlying cause**: Medications for autoimmune conditions (e.g., steroids for glomerulonephritis) or stopping nephrotoxic drugs. 3. **Postrenal Azotemia**: - **Relieve the obstruction**: This can be done through surgery, stone removal, or the insertion of a **catheter** or **stent** to bypass the obstruction. - **Manage kidney function**: If obstruction has caused significant kidney damage, dialysis may be required. --- ### **Conclusion**: **Azotemia** refers to the buildup of nitrogenous waste products, primarily **BUN** and **creatinine**, in the blood due to impaired kidney function. It can be caused by **prerenal**, **renal**, or **postrenal** conditions, each requiring different treatment approaches. Early diagnosis and treatment are crucial to prevent progression to **uremia** and irreversible kidney damage. ### Reference: - ### Connected Documents: -