Synovial fluid

7 DOH Abu Dhabi (HAAD) lab licensing practice questions on Synovial fluid, part of Urinalysis and Body Fluids. The first 7 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

1. Question 1 · Hard

   A 67-year-old woman with osteoarthritis of the right knee had an intra-articular corticosteroid injection 3 weeks ago. The knee is still swollen but not hot, and she is afebrile. Synovial fluid: clear, pale yellow, good viscosity; WBC 1.2 x 10^9/L (1,200/µL), 70% mononuclear cells; Gram stain negative. Under compensated polarized light there are many extracellular crystals: flat, irregular plates and blunt rods of varied size, some with positive and others with negative birefringence. No needle-shaped crystals are seen inside neutrophils, and there are no plates with notched corners. Which crystals are most likely present?

   1. ACorticosteroid crystals from the injection
   2. BCalcium pyrophosphate crystals of pseudogout
   3. CCholesterol crystals of a chronic effusion
   4. DMonosodium urate crystals of acute gout

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   Answer: A · Corticosteroid crystals from the injection

   Injected corticosteroid suspensions, such as triamcinolone or methylprednisolone esters, leave crystals in the joint that can persist for weeks. They are pleomorphic flat plates and rods, mostly extracellular, and individual crystals may show positive or negative birefringence, so they can be mistaken for urate or pyrophosphate. Urate crystals are needles with strong negative birefringence, and calcium pyrophosphate crystals are rhomboids and rods with weak positive birefringence; in an acute attack both are seen inside neutrophils in an inflammatory fluid. Cholesterol crystals are flat plates with notched corners, and none are present. The low, mainly mononuclear count fits a noninflammatory osteoarthritic effusion, and the injection history should be noted on the crystal report.

   • B: Calcium pyrophosphate crystals are rhomboids or rods with weak positive birefringence.
   • C: Cholesterol crystals are flat plates with notched corners, which are absent here.
   • D: Urate crystals are needles with strong negative birefringence, usually inside neutrophils.

2. Question 2 · Hard

   A 63-year-old man with known gout has a hot, swollen knee and a temperature of 38.9 °C. Synovial fluid: WBC 85 × 10^9/L (85,000/µL), 94% neutrophils, intracellular monosodium urate crystals, no organisms on Gram stain. What should the laboratory do?

   1. AReport gout and cancel the culture
   2. BReport the crystals and complete the culture
   3. CReport septic arthritis and omit the crystals
   4. DAsk for a new tap before reporting anything

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   Answer: B · Report the crystals and complete the culture

   Gout and septic arthritis can occur in the same joint, and finding crystals does not exclude infection. A WBC above about 50 × 10^9/L with more than 90% neutrophils and fever raises real concern for sepsis, and the Gram stain misses many infected joints. The crystals are reported, and the culture is completed so that infection is confirmed or excluded. A missed septic arthritis can destroy the joint within days.

   • A: Crystals do not rule out infection, so the culture is still needed.
   • C: The urate crystals are a real finding and must be reported.
   • D: The sample is adequate; delaying the report delays treatment.

3. Question 3 · Easy

   What is the approximate upper limit of the white cell count in normal synovial fluid?

   1. A2 × 10^9/L (2,000/µL)
   2. B0.2 × 10^9/L (200/µL)
   3. C20 × 10^9/L (20,000/µL)
   4. D50 × 10^9/L (50,000/µL)

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   Answer: B · 0.2 × 10^9/L (200/µL)

   Normal joint fluid has fewer than about 200 white cells/µL (0.2 × 10^9/L), mostly monocytes, macrophages and lymphocytes, with neutrophils under 25%. Counts up to about 2 × 10^9/L with few neutrophils suggest a noninflammatory effusion such as osteoarthritis. Counts in the tens of thousands per µL with many neutrophils suggest inflammatory arthritis, and counts above about 50 × 10^9/L with more than 90% neutrophils suggest septic arthritis. The groups overlap, so the count is read together with the crystal examination, Gram stain and culture.

   • A: About 2 × 10^9/L is the upper end of a noninflammatory effusion.
   • C: Around 20 × 10^9/L is typical of inflammatory arthritis.
   • D: Above about 50 × 10^9/L with many neutrophils suggests septic arthritis.

4. Question 4 · Medium

   A synovial fluid is so viscous that it cannot be pipetted accurately for a white cell count. What is the best way to prepare it?

   1. AHeat it in a 56 °C water bath
   2. BIncubate it with hyaluronidase
   3. CDilute it in 3% acetic acid
   4. DCount the cells in the sediment

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   Answer: B · Incubate it with hyaluronidase

   Synovial fluid is viscous because of its hyaluronic acid. A small amount of hyaluronidase breaks the hyaluronate down, so the fluid can be pipetted, mixed and diluted accurately for a manual or automated count. The enzyme does not damage the cells, but the added volume is allowed for if it is significant. Acetic acid must not be used, because it forms a mucin clot that traps the cells.

   • A: Heating is not a standard method and can damage the cells.
   • C: Acetic acid forms a mucin clot with hyaluronate and traps the cells.
   • D: Counting a sediment concentrates the cells and gives a falsely high count.

5. Question 5 · Hard

   A 74-year-old woman has an acutely swollen knee. Her synovial fluid contains weakly birefringent, rod- and rhomboid-shaped crystals inside neutrophils. With a red compensator they are blue when their long axis is parallel to the slow axis, and yellow when perpendicular. Which crystal and condition fit?

   1. AHydroxyapatite; calcific arthritis
   2. BCholesterol; chronic effusion
   3. CCalcium pyrophosphate; pseudogout
   4. DMonosodium urate; acute gout

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   Answer: C · Calcium pyrophosphate; pseudogout

   A crystal that is blue when parallel to the compensator's slow axis is positively birefringent. Weakly positive, rod-shaped or rhomboid crystals are calcium pyrophosphate dihydrate (CPPD), the cause of pseudogout, which most often affects the knee in older people. Monosodium urate is the opposite: needle-shaped, strongly birefringent, and yellow when parallel to the slow axis. Chondrocalcinosis on X-ray supports CPPD disease.

   • A: Hydroxyapatite crystals are too small to see singly and are not birefringent.
   • B: Cholesterol forms large flat plates with notched corners, usually outside cells.
   • D: Urate needles are strongly negative: yellow, not blue, when parallel.

6. Question 6 · Hard

   A 45-year-old woman with active rheumatoid arthritis has a knee effusion. Which synovial fluid result set fits her disease best?

   1. AWBC 150 × 10^9/L, 97% neutrophils, no crystals
   2. BWBC 25 × 10^9/L, 85% neutrophils, urate crystals
   3. CWBC 16 × 10^9/L, 70% neutrophils, no crystals
   4. DWBC 0.9 × 10^9/L, 20% neutrophils, no crystals

   Answer and explanation in LearnFree account

7. Question 7 · Medium

   Which collection tube is preferred for synovial fluid sent for crystal examination?

   1. APotassium oxalate
   2. BSodium heparin
   3. CPowdered EDTA
   4. DLithium heparin

   Answer and explanation in LearnFree account