Chapter 29: Body Fluid Analysis

1. Chapter 29: Body Fluid Analysis By Kristy Shanahan, Lillian A. Mundt

2. Amniotic Fluid (AF) • Functions • Provides cushioning medium for fetus • Regulates temperature of fetal environment • Allows fetal movement • Serves as matrix for influx & efflux of constituents • Sources • Mother is ultimate physiologic source for AF. • Other sources: maternal secretion across amnion, transudation across fetal skin, fetal micturition or urination

3. Amniotic Fluid (AF) (cont’d) • Dynamic balance between production & clearance of AF • Balance is maintained by fetal urination & swallowing. • AF sample contains cells originating from fetus & may be obtained by transabdominal amniocentesis. • Amniocentesis & subsequent AF analysis test for: • Congenital diseases • Neural tube defects • Hemolytic disease • Fetal pulmonary development

4. Amniotic Fluid (AF) (cont’d) • Neural Tube Defects (NTDs) • Elevated levels of -fetoprotein (AFP) associated with spina bifida, anencephaly, abdominal hernias into umbilical cord, cystic hygroma, & poor pregnancy outcome • Low maternal serum AFP associated with Down’s syndrome • Protocol for AFP testing: • 1. Serum AFP, assay of hCG, unconjugated estriol, & inhibin A • 2. Repeat if positive • 3. Diagnostic ultrasound • 4. Amniocentesis for confirmation

5. Amniotic Fluid (AF) (cont’d) • Hemolytic Disease of Newborn (HDN) • A syndrome of fetus resulting from ABO incompatibility of maternal & fetal blood • Maternal antibodies to fetal erythrocytes cause hemolytic reaction varying in severity. • Resultant hemoglobin breakdown products appear in AF & provide a measure of severity of incompatibility reaction. • Method of measurement: direct spectrophotometric scan of undiluted AF & calculation bilirubin • Treatment options: immediate delivery, intrauterine transfusion, or observation

6. Amniotic Fluid (AF) (cont’d) • Assessment of fetal prognosis

7. Amniotic Fluid (AF) (cont’d) • Fetal Lung Maturity • Primary reason for AF testing is assessment of fetal pulmonary maturity. • Testing indicates whether specific phospholipid levels are sufficient to prevent atelectasis (alveolar collapse) at delivery. • Risk factors to fetus or mother must be weighed against interventions. • Respiratory distress syndrome: alveolar collapse in neonatal lung during changeover from placental oxygen to air • Lung maturation is function of differentiation of alveolar epithelial cells into types I & II cells.

8. Amniotic Fluid (AF) (cont’d) • Fetal Lung Maturity • Tests for assessing fetal lung maturity • Functional assays: bubble or shake test, foam stability index • Quantitative assays: lecithin-sphingomyelin ratio (L/S ratio), phosphatidylglycerol, fluorescence polarization, lamellar body counts • Classic technique for separation & evaluation of lipids involves thin-layer chromatography of an extract of AF. • Classic breakpoint for judgment of maturity has been an L/S ratio of 2.

9. Amniotic Fluid (AF) (cont’d) • Thin-layer chromatogram of amniotic fluid phospholipids

10. Phosphatidylglycerol (PG) • A phospholipid essential for fetal lung maturity (FLM) is PG that increases in proportion to lecithin. • Development of PG is delayed in diabetic mothers. • Thus, L/S ratio of 2 cannot be relied upon unless PG is included in interpretation. • An immunologic assay using antibody specific for PG can be used to determine FLM .

11. Fluorescence Polarization • Compares polarization of a fluorescent dye that combines with albumin & surfactant in AF specimen • Lamellar Body Counts • Type II alveolar cells produce & secrete phospholipids in form of lamellar bodies. • As FLM increases, these lamellated packets of surfactant also exhibit an increased presence in AF. • The fact that lamellar bodies are about same size as platelets provides a convenient method to determine their concentration using platelet channel on automated hematology analyzers.

12. Cerebrospinal Fluid (CSF) • Description • Liquid that surrounds brain & spinal cord • Flows between arachnoid & pia mater in subarachnoid space • Total CSF volume is about 150 mL (8% of CNS cavity volume). • Functions • Physical support & protection • Provision of a controlled chemical environment for nutrient supply & waste removal • Intracerebral & extracerebral transport

13. Cerebrospinal Fluid (CSF) (cont’d) • Formation • Formed predominantly at choroid plexus deep within brain & by ependymal cells lining ventricles • Formed at average rate of 0.4 mL/min, or 500 mL/day • Formation results from selective ultrafiltration of plasma & active secretion by epithelial membranes. • Analysis • Investigated for cases of suspected CNS infection, demyelinating disease, malignancy, & hemorrhage in CNS • Normal CSF is clear, colorless, free of clots, & free of blood.

14. Cerebrospinal Fluid (CSF) (cont’d) • Analysis • Common reasons for blood to be found in CSF: traumatic tap & subarachnoid hemorrhage • Tests of interest: glucose, protein, lactate, glutamine • Plasma sample should be obtained 2–4 hours prior to tap so plasma & CSF glucose levels can equilibrate. • Decreased CSF glucose levels can be result of: • 1. Disorder in carrier-mediated transport of glucose to CSF • 2. Active metabolism of glucose by cells or organisms • 3. Increased metabolism by CNS

15. Cerebrospinal Fluid (CSF) (cont’d) • Analysis • Increased lactate level with a normal to decreased glucose level has been suggested as a readily accessible indicator for bacterial vs. viral meningitis. • Protein levels in CSF reflect selective ultrafiltration of CSF blood–brain barrier. • Increased level of CSF total protein is useful nonspecific indicator of pathologic states.

16. Sweat • Eccrine Sweat Glands • Regulate body temperature • Are innervated by cholinergic nerve fibers & are type of exocrine gland • Analysis • Generally not proven to be a clinically useful model • Used effectively, however, for determination of chloride levels in diagnosis of cystic fibrosis (CF)

17. Sweat (cont’d) • Analysis • Diagnostic algorithms for CF rely on abnormal sweat electrolytes, pancreatic or bronchial abnormalities, & family history. • Sweat glands, although affected in their secretion, remain structurally unaffected by CF. • Both sodium & chloride are measured in sweat, but chloride remains more important. • Standard method of measurement is based on pilocarpine nitrate iontophoresis method of Gibson & Cooke. • Other methods include osmolarity, conductivity, & chloride electrodes or patches placed on skin.

18. Synovial Fluid • Fluid found in the cavities of movable joints • Formed by ultrafiltration of plasma across synovial membrane • Serves as transport medium for delivery of nutrients & removal of cell wastes • Normal fluid is clear, colorless to pale yellow, viscous, & nonclotting. • Variations are indicative of pathologic conditions. • Sample is collected via arthrocentesis of joint.

19. Serous Fluids • Lungs, heart, & abdominal cavities are surrounded by 2 serous membranes: • Parietal membrane lining cavity wall • Visceral membrane lining organs • Serous fluids, ultrafiltrates of plasma, are located between membranes. • Formed by serum dialyzing across these membranes • 3 types: pleural (lung), pericardial (heart), peritoneal (abdominal)

20. Serous Fluids (cont’d) • Pleural Fluid • Essentially interstitial fluid of systemic circulation • Normally, there is 3–20 mL of pleural fluid in pleural space. • Fluid is removed from pleural space by needle & syringe. • Classifications • Transudate: secondary to remote pathology; indicates that treatment should begin elsewhere • Exudate: primary involvement of pleura & lung; demands immediate attention • Fluid is classified based on series of fluid/plasma ratios known as Light’s criteria.

21. Serous Fluids (cont’d) • Pericardial Fluid • Relationship of pericardium, pericardial fluid, & heart is similar to that of pleura, pleural fluid, & lungs; formation & drainage are same. • Pericardial sampling & lab analysis is rare. • Peritoneal Fluid • Excess fluid (>50 mL) in peritoneal cavity indicates disease. • Presence of excess fluid is ascites, & fluid is called ascitic fluid. • Samples are obtained by needle aspiration (paracentesis). • Exudative causes of ascites are metastatic ovarian, prostate, & colon cancer, & infective peritonitis.