Renal

Kidney Functions and Key Facts

Acts as the body’s fluid regulator.
Water balance is controlled by antidiuretic hormone (ADH) and aldosterone.
Eliminates water-soluble waste, including creatinine, urea, and uric acid.
Produces essential substances such as erythropoietin (which stimulates red blood cell production in the bone marrow), renin, bradykinin, prostaglandins, and calcitriol (active vitamin D3).
Normal urine output averages 1,500 mL per day.
Oliguria is defined as urine output of less than 400 mL per day.
The right kidney sits lower than the left due to displacement by the liver.

Urinalysis: Key Indicators and Their Significance

Epithelial Cells: A few are normal, but large quantities suggest contamination.
Leukocytes: Normal white blood cell (WBC) count in urine is less than 10.
- Leukocyte esterase: Can indicate infection or inflammation.
- Pyuria (WBCs in urine): Always abnormal in males.
Urine Culture & Sensitivity: Bacterial count greater than 100,000 suggests infection.
Red Blood Cells (RBCs): Fewer than 5 per high-power field is considered normal.
Protein: May indicate kidney damage.
- Standard urine dipstick detects albumin but not microalbumin (such as Bence-Jones proteins).
Nitrites: Presence suggests a bacterial infection.
Casts (Cylindrical structures in urine):
- Hyaline casts: Can be a normal finding.
- WBC casts: Often associated with infections.
- RBC casts with proteinuria: Strongly indicative of glomerulonephritis.

Kidney Function: Key Markers and Interpretation

Serum Creatinine: Inversely related to kidney function—when renal function declines, creatinine levels rise.
- Influenced by age (less reliable in elderly), gender (higher in males), ethnicity (higher in individuals of African descent), and muscle mass.
- Normal Range:
  - Males: 0.7 – 1.3 mg/dL
  - Females: 0.6 – 1.1 mg/dL
Estimated Glomerular Filtration Rate (eGFR):
- Provides an estimated measure of kidney function—the more damaged the kidneys, the lower the eGFR.
- Best measured when the patient avoids meat consumption for 12 hours before testing.
- Less reliable in cases of significant muscle mass changes, pregnancy, or acute kidney failure.
- eGFR Stages:
  - Normal: > 90
  - Stage 2: 60 – 89
  - Stage 3a: 45 – 59
  - Stage 3b: 30 – 44
  - Stage 4: 15 – 30
  - Stage 5 (Kidney Failure): < 15
Blood Urea Nitrogen (BUN):
- Elevated levels may indicate acute kidney failure, high-protein intake, hemolysis, congestive heart failure (CHF), or medication effects.
- BUN rises when protein waste accumulates in the blood; dehydration can also lead to increased BUN levels.
BUN-to-Creatinine Ratio:
- Helps assess dehydration, low blood volume (hypovolemia), and acute kidney injury.

Kidney Conditions: Causes of Azotemia

Prerenal Azotemia: The leading cause of acute kidney failure, resulting from reduced blood flow to the kidneys, which may progress to acute tubular necrosis.
- Triggered by decreased circulating volume (e.g., dehydration, acute blood loss), reduced cardiac output (e.g., heart failure), or fluid sequestration (e.g., severe burns).
Postrenal Azotemia: A less common cause of kidney failure, occurring due to urinary flow obstruction.
- May result from glomerulonephritis or other blockages affecting normal urine drainage.

Chronic Kidney Disease (CKD): Key Facts and Considerations

Common Electrolyte Imbalances: Elevated sodium (hypernatremia), calcium (hypercalcemia), and potassium (hyperkalemia).
Creatinine and Renal Function:
- A rise in creatinine from 1 to 2 mg/dL suggests a 50% decline in kidney function.
- Creatinine clearance typically reflects estimated glomerular filtration rate (eGFR).
- Creatinine is a metabolic byproduct of skeletal muscle breakdown.
Primary Causes of CKD:
- Diabetes mellitus (DM)
- Recurrent pyelonephritis
- Polycystic kidney disease
Early Indicators:
- Persistent proteinuria is often present in the early stages of CKD.
Medications and Treatment Approaches:
- ACE inhibitors (ACEIs) help slow CKD progression by reducing resistance in the efferent arterioles.
Glomerulonephritis Findings:
- Edema, red blood cell (RBC) casts, and proteinuria.
Anemia in CKD:
- Typically normocytic, normochromic with a low reticulocyte count.
- Erythropoiesis-stimulating therapy recommended if hemoglobin (Hgb) falls below 10 g/dL.
Advanced CKD Management:
- Dialysis or kidney transplant discussions should begin at Stage 4 CKD.
Medications Affecting Kidney Function:
- Allopurinol, certain antibiotics, digoxin, lithium, gabapentin, H2 blockers, and antiarrhythmics can impact renal function.

Condition	Cause	Signs & Symptoms	Diagnostic Tests	Treatment Options	Concerns
Pyelonephritis	Commonly caused by E. coli, Klebsiella, and Proteus mirabilis.	High fever, chills, nausea, vomiting, painful urination, frequent urination, and deep, unilateral flank pain. Often preceded by a urinary tract infection (UTI).	Costovertebral angle (CVA) tenderness on exam. Urinalysis (UA) shows large leukocytes, hematuria, white blood cell (WBC) casts, and proteinuria. Urine culture and sensitivity (C&S) confirm the pathogen.	Outpatient treatment for uncomplicated cases includes Ciprofloxacin (Cipro) for 7 days or Levofloxacin (Levaquin) once daily. For more severe cases: Ceftriaxone (Rocephin) 1g plus Augmentin for 14 days.	If untreated, it can lead to sepsis, kidney damage, or chronic infections.
Acute Renal Failure	Can result from reduced kidney blood flow, direct kidney damage, or urinary obstruction.	Sudden onset of reduced urine output, fluid retention (swelling and weight gain), fatigue, nausea, and appetite loss.	Elevated creatinine and decreased glomerular filtration rate (GFR).	Hydration and addressing underlying causes.	If not treated promptly, it may progress to chronic kidney disease.
Bladder Cancer	Long-term use of pioglitazone is a risk factor. Other risks include smoking and exposure to industrial chemicals.	Painless blood in urine (microscopic or visible), possibly more noticeable at the end of urination. Frequent urination, discomfort, nocturia. Advanced cases may cause pelvic, lower abdominal, or bone pain.	Urinalysis (UA) may reveal microscopic hematuria. Urine culture & sensitivity (C&S) rule out infection. Urine cytology can detect cancerous cells.	For non-muscle-invasive cases, treatment involves transurethral resection followed by intravesical chemotherapy.	High recurrence rate even after successful treatment.
Hematuria	Causes include infections, kidney stones, cancer, blood disorders, glomerular disease, trauma, and medications (e.g., anticoagulants).	Urine may appear pink, red, or brown, with or without blood clots.	Urinalysis (UA). Urine C&S if an infection is suspected. Urine cytology if malignancy is a concern.	Treatment depends on the underlying cause.	Further evaluation is needed if persistent or associated with other symptoms.
Urinary Tract Infection (Cystitis)	Typically caused by E. coli, Klebsiella, Staphylococcus saprophyticus, and Proteus mirabilis.	Burning, frequent urination, urgency, hematuria, foul-smelling urine, nocturia, lower abdominal or back pain. No fever.	Urinalysis: Moderate to large leukocytes, possible nitrites, few RBCs. Urine C&S if needed.	Uncomplicated UTI: Bactrim DS for 3 days or Nitrofurantoin (Macrobid) for 5 days. Avoid fluoroquinolones in pregnancy and children under 18. Complicated UTI: Cefalexin (Keflex) or Levofloxacin (Levaquin) for 7-10 days. Phenazopyridine (Pyridium) for symptom relief (turns urine orange).	In men, a prostate exam is necessary. Pregnant women with asymptomatic bacteriuria should be treated. Young children and pregnant women are at higher risk of progression to pyelonephritis.
Kidney Stones (Nephrolithiasis/Urolithiasis)	Most are composed of calcium oxalate. Struvite stones occur in those with recurrent kidney infections.	Intense, intermittent flank or abdominal pain, often causing restlessness. May be accompanied by nausea, vomiting, and hematuria. Stones in the upper urethra cause flank pain; stones in the lower urethra may radiate pain to the groin, testicles, or labia.	Imaging (CT scan or ultrasound). UA may show hematuria.	NSAIDs (e.g., ketorolac/Toradol) for pain, increased hydration, and urine straining. Dietary changes to reduce oxalate intake (e.g., avoiding spinach, beets, chocolate, tea, and meats). Alpha-blockers may aid stone passage. Referral to urology if needed.	Risk factors include family history, gout, bariatric surgery, high-dose vitamin C. Medications like HCTZ, topiramate, and indinavir can contribute to stone formation.
Glomerulonephritis	Inflammation of kidney glomeruli, often following a bacterial infection (1-2 weeks post-infection).	Dark or cola-colored urine (hematuria), foamy urine (proteinuria), hypertension, swelling in the face, hands, feet, or abdomen. Possible anemia.	UA: Increased protein, RBCs, renal casts. Elevated creatinine and blood urea nitrogen (BUN). Imaging (CT scan or kidney ultrasound). Kidney biopsy confirms diagnosis.	Acute cases may resolve on their own. Treatment includes blood pressure control, antibiotics (if infectious), corticosteroids, and immunosuppressants. Severe cases may require plasmapheresis or dialysis.	If untreated, it may lead to kidney failure, hypertension, or nephrotic syndrome. Risk factors include infections (e.g., bacterial endocarditis), autoimmune diseases (e.g., lupus, Goodpasture’s syndrome), and vasculitis.