LDH – Pleural Fluid:
Why LDH Pleural Fluid Test ?
CLINICAL INFORMATION
In General, the enzymes within the cell (cytosol) are impermeable to cell membranes (hence these cellular enzymes cannot enter blood circulation easily) and thus these enzyme activities are very low compared to those within the cell. LDH is also known as ‘lactate dehydrogenase’. This enzyme catalyzes the conversion of lactate to pyruvate. LDH is present in almost every cell in the body- including blood (serum and/or plasma), muscles, brain (CSF sample specimen collected by lumbar puncture also known as a spinal tap), kidneys, liver, lung (eg. empyema), pancreas etc. “Iso-Enzymes” are the multiple forms of the same enzyme that differ in physical properties but they have the same function (similar catalytic activity) eg- they bind to the same substrates (or in other words - They are different variants of the same enzyme having identical functions). Iso-enzymes are of utmost clinical interest since they can be used as molecular markers of tissue damage. The iso-forms of LDH are LDH-1: present in the heart, brain and RBCs, LDH-2: present in the RES – Reticulo-Endothelial System, LDH-3: present in the lungs, LDH-4: present in the kidney, placenta and the pancreas, LDH-5: present in the liver, striated muscles and the brain. LDH test measures the amount of LDH enzyme present in the blood and/or other body fluids. Hence this test looks for signs of damage to the body tissues (eg. Myocardial infarction) and also to know the extent of injury in case of heart, liver, kidney diseases etc. This test is a helpful tool in conditions like hemolytic and/or megaloblastic anaemia, prognosis in cancer treatment etc. The sample specimen is usually an intra-vascular fluid eg. Blood (serum/plasma) and/or body or bio-fluids. High levels of LDH are found in certain pathological conditions such as anaemia, liver diseases, muscle injury, kidney diseases, heart attack (myocardial infarction), pancreatitis, infections like infectious mononucleosis, and encephalitis, meningitis etc, certain cancer types including leukaemia, lymphoma etc. Additional tests include the Troponin-1 (the diagnosis of infarction has been largely superseded by this test) test. Supporting tests include other serum levels of skeletal muscle enzymes or proteins that serve as markers in pathological conditions eg. Creatine kinase (CK), aldolase, myoglobin, troponin, aspartate aminotransferase, carbonic anhydrase CAIII. But in physiological conditions too for example in strenuous exercises – muscle injury mediated by apoptosis may occur triggered by increased oxidative stress and hence other markers may serve as an important tool like thiobarbituric acid- reactive substances, malondialdehyde, sulfhydryl groups, reduced glutathione, oxidized glutathione, super-oxide dismutase, catalase etc. Other tests include ESR, D-dimer, CRP, enzymatic assays or colourimetric, HPLC, spectrophotometry etc.
Pleural Fluid(specimen fluid) is collected from pleural space (area between the lining of the lungs – ‘Pleura’, and in between the chest wall by thoracentesis - needle inserted between the ribs to aspirate pleural fluid biopsy). The pleural fluid aspirate is done to perform analysis to find the cause of pleural effusion, to differentiate it, either of a transudate or exudate – in origin (for differential diagnosis), which has caused that extra fluid leak into the pleural space. Therefore the test results (confirm a definitive diagnosis), hence determining the mode of treatment needed, accordingly. For eg. if the pleural effusion is confirmed from the specimen analysis (of an exudative type), medical treatment is initiated as required. Test on the pleural fluid is performed to differentiate between transudates (it is a filtrate of blood caused due to increased pressure in veins and capillaries that forces fluid through vessel walls or to a low level of protein in blood serum and since transudate accumulates in tissue outside the blood vessels hence causes edema) and exudates (the fluid that filters from the circulatory system into lesion or areas of inflammation which is usually comprised of serum, fibrin and leucocytes). This differentiation is based on fluid albumin level i.e the Serum-Ascites Albumin Gradient (SAAG) calculation, which is serum albumin level minus the fluid albumin level will distinguish if it is a case of exudate or transudate. Most common causes of lung and pleural injuries include injuries of the chest (physical trauma), viral, fungal, bacterial causes of pleural effusion are due to Streptococcus milleri group, Streptococcus pneumonia, Streptococcal aureusetc and also by autoimmune diseases, rheumatoid arthritis, tuberculosis etc. Symptoms of pleural effusion include chest pain, dry and non-productive cough, dyspnea, orthopnea etc. Some of the complications of pathology causing pleurisy may include lung damage, an infection that turns into an abscess called empyema, empyema (an infection that turns into an abscess, pneumothorax (air in chest cavity after pleural effusion), pleural thickening (scarring of the lining of the lung) etc.
Hence LDH pleural fluid test is performed to screen to detect the underlying pathology in the lungs.
General Instructions:
Sample Requirement: Specimen - Pleural fluid. Test Preparation: None.
NOTE - Sample for specimen collections may vary based on the patient’s condition / cases according to the patient’s presenting complaints/signs or symptoms:
SPECIMEN REQUIREMENT (Special or Rare Cases) - As instructed and guided by Physician / Clinician / Pathologist / as per Laboratory’s requirements, according to procedures and protocols.
This Multi-Specialty Clinical Referral Laboratory RT DIAGNOSTICS provides precise and accurate tests with an extensive range of testing services to the medical centres to help in the diagnosis and identification of pathology in the test specimens for infectious diseases and also to evaluate the function of organ systems of the patient. It prevents further complications and helps to stabilize and restore health to near normalcy at the earliest without delay.
