Lactate Dehydrogenase (LDH Ascitic Fluid)

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Measures LDH enzyme.

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Lactate Dehydrogenase (LDH Ascitic Fluid) - Comprehensive Medical Test Guide

Section 1: Why is it done?
- Test Overview: LDH (Lactate Dehydrogenase) is an enzyme found in cells throughout the body. This test measures LDH levels in ascitic fluid (fluid that accumulates in the abdominal cavity). The LDH level helps differentiate the cause of ascites and determine if the fluid is due to liver disease, infection, malignancy, or other serious conditions.
- Primary Reasons for Ordering: To determine the classification of ascites as transudate (non-inflammatory) or exudate (inflammatory), which aids in diagnosing the underlying cause of fluid accumulation
- Diagnostic Indications: Suspicion of bacterial peritonitis, malignant ascites, hepatic cirrhosis, portal hypertension, pancreatic disease, kidney disease, heart failure, tuberculosis, or other causes of peritoneal inflammation or infection
- Clinical Circumstances: When a patient presents with unexplained abdominal swelling, fever with ascites, suspected peritonitis, new onset ascites of unclear etiology, or during diagnostic paracentesis (abdominal fluid tap)
- Timing of Testing: Performed during or immediately after paracentesis (fluid aspiration); typically done as part of initial ascitic fluid analysis workup for diagnostic purposes
Section 2: Normal Range
- Reference Values: Normal ascitic fluid LDH is typically less than 400 IU/L (International Units per Liter), though values may vary slightly between laboratories. Some laboratories use a cutoff of less than 200-240 IU/L depending on their reference ranges.
- Units of Measurement: IU/L (International Units per Liter) or U/L (Units per Liter)
- Interpretation of Results:
  - Low/Normal LDH (<400 IU/L): Suggests a transudate, typically associated with non-inflammatory causes such as cirrhosis, portal hypertension, heart failure, or nephrotic syndrome
  - Elevated LDH (>400 IU/L): Suggests an exudate, indicating inflammatory or infectious processes such as bacterial peritonitis, malignant ascites, tuberculosis, or pancreatitis
  - Critical/Very High LDH (>1000 IU/L): May indicate spontaneous bacterial peritonitis, malignant ascites with significant cellular involvement, or severe inflammatory conditions requiring urgent intervention
- Clinical Significance of Normal vs Abnormal: Normal results support non-inflammatory causes, while elevated levels suggest the need for further investigation into infectious, malignant, or inflammatory etiologies. Results should always be interpreted in conjunction with other ascitic fluid parameters such as protein, glucose, albumin, and cell counts.
Section 3: Interpretation
- Transudate vs Exudate Classification: LDH is one of several parameters used to classify ascites. A serum-to-ascitic LDH ratio is often calculated. If ascitic LDH is greater than 2/3 of the upper limit of serum LDH, this suggests exudative ascites.
- Differentiation of Ascites Causes:
  - Low LDH with High Protein: May suggest malignancy or tuberculosis; further investigation with cytology and cultures recommended
  - High LDH with Positive Cultures: Indicates bacterial or fungal infection requiring antibiotic or antifungal therapy
  - High LDH with Elevated WBC: Suggests inflammatory or infectious process, particularly if neutrophils are predominant (spontaneous bacterial peritonitis)
  - High LDH with Malignant Cells: Indicates malignant ascites; correlates with disease burden and prognosis
- Factors Affecting Results:
  - Hemolysis: Blood contamination during paracentesis can falsely elevate LDH levels; results may need to be recollected
  - Cell Count: Higher white blood cell counts correlate with elevated LDH; interpretation must account for cell concentration
  - Time to Processing: Delayed processing can result in cell lysis and falsely elevated LDH; specimens should be processed promptly
  - Laboratory Variation: Different laboratories may use different reference ranges and methodologies; comparison should be made to facility-specific normal values
- Clinical Significance of Result Patterns: LDH elevation must be interpreted as part of the complete ascitic fluid profile including total protein, albumin-ascites gradient (AAG), glucose, cell counts and differential, and culture results. The combination of parameters provides diagnostic specificity superior to any single test.
Section 4: Associated Organs
- Primary Organ Systems Involved:
  - Liver: Primary organ in hepatic cirrhosis and portal hypertension, the most common causes of ascites globally
  - Peritoneum: Serous membrane that lines the abdominal cavity and viscera; directly involved in peritonitis and inflammatory ascites
  - Heart: Involved in ascites secondary to congestive heart failure and right ventricular dysfunction
  - Kidneys: Related to nephrotic syndrome and renal failure causing ascites through protein loss and fluid retention
  - Pancreas: Involved in pancreatic ascites from acute or chronic pancreatitis, particularly with pancreatic duct disruption
- Medical Conditions Associated with Abnormal Results:
  - Infections: Spontaneous bacterial peritonitis (SBP), secondary bacterial peritonitis, tuberculosis peritonitis, fungal infections
  - Malignancies: Peritoneal carcinomatosis, ovarian cancer, gastric cancer, liver cancer, pancreatic cancer, peritoneal mesothelioma
  - Inflammatory Conditions: Acute or chronic pancreatitis, lupus peritonitis, vasculitis, inflammatory bowel disease with perforation
  - Hepatic Disorders: Cirrhosis from viral hepatitis, alcohol, NAFLD, autoimmune hepatitis, hemochromatosis, primary biliary cirrhosis
  - Cardiovascular Conditions: Congestive heart failure, constrictive pericarditis, restrictive cardiomyopathy, right ventricular infarction
  - Renal Disorders: Nephrotic syndrome, acute kidney injury, chronic kidney disease with severe proteinuria
- Potential Complications Associated with Abnormal Results:
  - Sepsis and Shock: Untreated bacterial peritonitis can progress to sepsis and multi-organ failure if antibiotics are delayed
  - Hepatic Encephalopathy: Spontaneous bacterial peritonitis can precipitate hepatic encephalopathy in cirrhotic patients
  - Acute Kidney Injury: Can occur with severe peritonitis or related to systemic complications
  - Peritoneal Fibrosis: Chronic peritonitis, especially from tuberculosis, can lead to peritoneal fibrosis and adhesions
  - Disease Progression: Elevated LDH may correlate with worse prognosis in malignant ascites and indicates advanced disease
Section 5: Follow-up Tests
- Recommended Complementary Ascitic Fluid Tests:
  - Total Protein: Used alongside LDH to classify ascites; <2.5 g/dL suggests transudate, >2.5 g/dL suggests exudate
  - Serum-Ascites Albumin Gradient (SAAG): Essential for differentiating portal hypertension-related ascites (SAAG ≥1.1) from other causes
  - Glucose: Low glucose (<50 mg/dL) suggests bacterial peritonitis or malignancy; very helpful in diagnosis
  - Cell Count and Differential: WBC >1000/µL or >250 PMN/µL suggests infection; high lymphocytes suggest TB or malignancy; presence of RBC indicates bleeding
  - Culture and Gram Stain: Mandatory when peritonitis is suspected; culture bottles should be inoculated immediately for optimal yield
  - Cytology: Important when malignancy is suspected; sensitivity increases with repeated samples
  - Amylase: Ascitic amylase >serum amylase suggests pancreatic ascites
  - AFB Stain and TB Culture: When tuberculous peritonitis is suspected; culture is more sensitive than smear
- Additional Diagnostic Investigations:
  - Serum LDH: For calculating serum-to-ascitic LDH ratio to classify ascites
  - Liver Function Tests: AST, ALT, alkaline phosphatase, bilirubin to assess hepatic function
  - Serum Albumin: For SAAG calculation and assessing protein status
  - Prothrombin Time/INR: To assess coagulopathy; important before invasive procedures
  - Imaging Studies: Ultrasound or CT imaging of abdomen to evaluate underlying pathology, peritoneal thickening, masses
  - Endoscopy: When variceal bleeding is suspected as cause of ascites
- Monitoring Frequency and Follow-up Paracentesis:
  - Bacterial Peritonitis: Repeat paracentesis may be indicated 48 hours after antibiotic initiation to document improvement (PMN count should decrease >30%)
  - Malignant Ascites: Repeat cytology may be performed if initial result was negative but clinical suspicion remains high
  - Portal Hypertension Monitoring: Regular paracentesis may be needed for symptom management; repeat testing only if clinical status changes significantly
Section 6: Fasting Required?
- Fasting Requirement: NO - Fasting is not required for ascitic fluid LDH testing
- Reason: The test is performed on ascitic fluid obtained via paracentesis, not blood. The collection method and specimen type are not affected by food intake.
- Patient Preparation Instructions:
  - Pre-Procedure: Patient should void bladder completely before paracentesis; wear comfortable, loose clothing; may eat normally
  - Positioning: Patient typically lies supine or semi-upright during paracentesis; position aids fluid accumulation at accessible sites
  - Skin Preparation: Abdomen will be cleansed with antiseptic solution; local anesthesia will be administered at insertion site
- Medications to Avoid or Modify:
  - Anticoagulants: Warfarin, apixaban, rivaroxaban, dabigatran should be held or dose adjusted; discuss with provider before procedure. INR and PT should be checked beforehand.
  - Aspirin and NSAIDs: Should be discontinued 5-7 days before procedure to minimize bleeding risk
  - Heparin Products: Unfractionated heparin or low-molecular-weight heparin should be discontinued prior to paracentesis per protocol
  - Other Medications: Most other medications may be continued; consult with physician regarding specific medications
- Specimen Collection and Handling:
  - Collection Container: Sterile tube, typically 10-20 mL of ascitic fluid; may be collected in different tubes depending on tests ordered
  - Processing Time: Specimens should be transported to laboratory promptly (preferably within 15-30 minutes) to prevent cell lysis and false elevation of LDH
  - Temperature: Keep specimen at room temperature for routine analysis; refrigerate if culture is being done to prevent bacterial overgrowth
  - Labeling: Specimen must be labeled as 'Ascitic Fluid' with patient identification, collection date/time, and 'STAT' if urgent testing is needed
- Post-Procedure Care:
  - Observation: Patient is monitored for vital signs; remain supine for 30 minutes post-procedure to reduce complication risk
  - Dressing: Puncture site is covered with sterile dressing; keep area clean and dry
  - Activity: Limit activity for 24 hours; avoid heavy lifting or strenuous exercise
  - When to Seek Medical Attention: Report fever, persistent abdominal pain, bleeding from puncture site, severe dizziness, or signs of peritonitis

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