MLPAO Urinalysis and Body Fluids Advanced Practice Flashcards

What are the different types of peritoneal fluid analysis performed in suspected spontaneous bacterial peritonitis (SBP)?

Answer: Cell count with differential (WBC >250 neutrophils/µL diagnostic), protein, albumin, glucose, LDH, Gram stain, and culture (in blood culture bottles)

SBP diagnosis is based on ascitic fluid polymorphonuclear (PMN) count >250 cells/µL. Additional analysis includes total protein, albumin (SAAG = serum albumin - ascitic albumin; >11 g/L suggests portal hypertension), glucose, LDH, Gram stain, and culture. Inoculating ascitic fluid into blood culture bottles at the bedside increases culture sensitivity from ~50% to ~80%.

What is the significance of xanthochromia in cerebrospinal fluid?

Answer: A yellow discolouration of CSF supernatant indicating the presence of hemoglobin degradation products (bilirubin, oxyhemoglobin), suggesting subarachnoid hemorrhage at least 2-4 hours old

Xanthochromia (yellow discolouration of CSF supernatant after centrifugation) indicates in vivo hemoglobin degradation, distinguishing subarachnoid hemorrhage (SAH) from traumatic tap. It develops 2-4 hours after SAH as RBCs lyse and hemoglobin is converted to oxyhemoglobin and then bilirubin. Spectrophotometric analysis provides objective xanthochromia assessment.

What is the serum-ascites albumin gradient (SAAG) and how is it used?

Answer: SAAG = serum albumin - ascitic fluid albumin; ≥11 g/L indicates portal hypertension; <11 g/L indicates non-portal hypertensive causes

SAAG is calculated by subtracting the ascitic fluid albumin from the serum albumin. A SAAG ≥11 g/L (1.1 g/dL) indicates portal hypertension with 97% accuracy (cirrhosis, heart failure, Budd-Chiari). SAAG <11 g/L suggests non-portal hypertensive causes (malignancy, TB peritonitis, nephrotic syndrome, pancreatitis). SAAG has replaced the traditional transudate/exudate classification for ascites.

How should a CSF specimen be prioritized if the volume is limited?

Answer: Cell count and differential first (tube 1), then chemistry/serology (tube 2), then microbiology (tube 3 — least likely contaminated)

When CSF volume is limited, prioritization depends on clinical suspicion. Generally: Tube 1 (cell count — most affected by traumatic tap, so use first tube), Tube 2 (chemistry/protein/glucose), Tube 3 (Gram stain and culture — last tube is least contaminated by blood from traumatic tap). However, if meningitis is strongly suspected, microbiology may take priority.

What is the significance of finding eosinophils in a pleural fluid?

Answer: Pleural eosinophilia (>10% eosinophils) suggests parasitic infection, drug reaction, malignancy, or prior pneumothorax/hemothorax

Pleural eosinophilia (>10% eosinophils in pleural fluid) has a specific differential diagnosis including parasitic infection, drug-induced pleuritis, malignancy (especially lymphoma), and prior air or blood in the pleural space. It notably makes tuberculosis very unlikely (<1% of TB effusions have eosinophilia), which can be diagnostically useful.

What automated method is used for urine chemistry in high-volume clinical laboratories?

Answer: Automated urine chemistry analyzers (Clinitek Atlas, Atellica, Cobas u701) that use reflectance photometry to read and standardize dipstick results

Automated urine analyzers use reflectance photometry to objectively read reagent strip colour changes, eliminating the subjectivity of manual visual reading. Instruments like the Roche Cobas u701, Siemens Clinitek, and Beckman Atellica standardize timing, minimize human error, and provide consistent semi-quantitative results with audit trails.