Renal Conditions, Urinalysis, and Hyponatremia

Renal Conditions and Lab Tests

• Order lab tests for patients with comorbidities and kidney damage, including HIV, lupus, and syphilis to rule out potential causes.

Secondary Membranous Nephropathy

• SLE, Hep B & C, and syphilis can cause the secondary membranous nephropathy (nephrotic syndrome).

Urinalysis Interpretation

• Understand how to interpret urinalysis results (osmolality, sodium, etc.) in conjunction with serum levels.
• Low ECV indicates a "sodium avid state".
• Pre-renal AKI is associated with BUN/Cr > 20 and FeNa < 1%.
• Low ECV leads to increased renin activation, resulting in sodium and water retention.
• Low ECV leads to low urinary sodium (< 20).
• Tonicity reflects the ability of a solution to move water in/out of a cell.
• Tonicity is calculated as osmolality minus ineffective osmoles (BUN).
• Osmolality includes Na+, BUN, and glucose.
• Tonicity is primarily determined by Na+ and glucose.

Hyponatremia Types

• Hypovolemic hyponatremia occurs in patients with vomiting or diarrhea, urine sodium < 20, and urine osmolality > 200.
• Hypervolemic hyponatremia is seen in patients with CHF, cirrhosis, or nephrotic syndrome, urine sodium < 20, and urine osmolality > 200.
• Hypotonic hyponatremia is characterized by low serum sodium (Na+ < 135 mEq/L) and low serum osmolality (< 275 mosm/kg).
• Hypertonic hyponatremia occurs with low serum sodium (Na+ < 135 mEq/L) and normal serum osmolality, often due to additional effective osmoles like glucose.
• Pseudohyponatremia is suspected when there's no explanation for increased osmolality and ineffective osmoles (BUN, alcohols) are present, but it may also be a lab error.
• Euvolemic hyponatremia has urine sodium > 20.

Acid-Base Abnormalities

• Acidosis occurs when there is not enough acid secretion.
• Alkalosis occurs with too much acid secretion.

Acid-Base Balance

• Proximal tubule reabsorbs bicarbonate.
• Distal tubule regenerates bicarbonate.
• Damage to either tubule can result in metabolic acidosis.

Anion Gap Calculation

• AG = Na+ - HCO3- - Cl-, with normal AG being albumin x 2.5.

High Anion Gap

• Elevated anion gap may indicate lactic acid from septic shock or ketoacidosis, or methanol poisoning.

Non-Anion Gap Metabolic Acidosis

• Non-anion gap metabolic acidosis can be caused by kidney or GI loss of bicarbonate.
• Type 1 distal RTA (collecting duct) has decreased net H+ secretion.
• Type 4 RTA involves true or mimics Aldo deficiency/resistance (distal).
• Proximal type 2 RTA causes wasting of filtered bicarbonate and is associated with Fanconi's syndrome.

Filtration vs. Secretion

• Inulin is freely filtered but not secreted and is the gold standard for kidney function assessment.
• Creatinine-based estimates are commonly used, creatinine is freely filtered & secreted in the kidneys, and serum creatinine is a late indicator of acute kidney injury.

Management of Vomiting and Diarrhea Complications

• Address hypovolemia with fluids.

Renal Effects of Infections

• All types of renal (intrinsic) AKI have active urine sediment.

Components of Urinalysis

• Urinalysis assesses WBCs, RBCs, casts, and protein.
• Glowing urine color indicates excess bilirubin.
• Proteinuria indicates glomerular damage.
• Damaged podocytes have an appearance of effacement (smushed together).
• Dark granular casts are caused by acute tubular necrosis (ATN), hypotension, septic shock and some medications.
• Acute/chronic interstitial nephritis (AIN) has Pyuria and is caused by UTI, drugs (i.e abx, proton pump inhibitors) and autoimmune disease.

Glomerular Disease

• Nephritic syndrome has <3.5 g/d of protein in the urine, while nephrotic syndrome has >3.5 g/d.
• Nephritic syndrome can manifest as Berger's disease (IgA nephropathy).
• Lupus nephritis with subendothelial immune deposits is typically nephritic and is with full house staining.
• Causes of nephrotic syndrome include DVT, Minimal change disease, and membranous nephropathy which is associated with Surface antigen PLA2R+.

Staging of Chronic Kidney Disease (CKD)

• eGFR is used for staging CKD, drug dosing, clinical trial eligibility, and kidney donation.
• Management includes free water restriction and consider other treatments, also be aware of the causes that may require an ICU.

Acute Kidney Injury

• The initial management of acute kidney injury when the patient isn't putting out any urine consists of treating by removing the obstruction.

Hepatorenal Syndrome

• Hepatorenal syndrome is liver failure → Splanchnic vasodilation → RAAS activation.

Pulmonary Fibrosis

• Smoking slows FEV1 decline, but lost lung function cannot be regained.

Lung Disease

• ARDS can lead to mechanical ventilation and worsening lung injury.
• Pneumonia is managed by identifying and targeting the pathogen.
• The indications for testing, basics of the standard PFT maneuver, Spirometry: Forced Vital Capacity maneuver, technique, and effort

Obstructive Sleep Apnea (OSA)

• The Mallampati test is an assessment for OSA (obstructive sleep apnea).