Physical

The physical examination is your first look at the crime scene. Before you bring in the high-tech chemical analyzers or the fancy microscopes, your own eyes and senses can give you a massive amount of information. These initial observations are critical—they provide immediate clues, help you prioritize your next steps, and can even be diagnostic on their own. It’s the foundation upon which all other testing is built. So, let’s get our eyes sharp and dive in!

General Concepts: Color and Clarity

Across almost all non-blood body fluids, the two most important physical characteristics we assess are color and clarity (also called turbidity). We have to be systematic in how we describe them

• Color: This tells us if substances are present that shouldn’t be. We always view the specimen in a clear tube against a white background
  • Red/Pink/Smoky: Usually indicates the presence of red blood cells. The question then becomes, is it from a disease process (hemorrhage) or a traumatic collection?
  • Yellow/Orange/Brown: Can indicate the breakdown of old red blood cells (leading to bilirubin formation, a condition we call xanthochromia), the presence of bilirubin from liver disease, or even high protein levels
  • Green/Purulent: Often a screaming sign of infection, with the color coming from the presence of neutrophils and bacteria
  • Milky/White: This can suggest a high number of white blood cells (infection) or the presence of lipids/chyle (from lymphatic obstruction)
• Clarity/Turbidity: This describes how clear the fluid is and is a rough indicator of the number of suspended particles. We grade it on a simple scale
  • Clear: Like water. You can easily read newsprint through it
  • Hazy: Some visible particles, but you can still mostly read newsprint
  • Cloudy: Newsprint is blurry or hard to read
  • Turbid/Opaque: You cannot see the newsprint at all
  • What causes turbidity?: The culprits are usually cells (WBCs, RBCs, tissue cells), microorganisms (bacteria, fungi), crystals, or lipids

Fluid-Specific Physical Characteristics

Let’s break down what we’re looking for in specific fluids

Cerebrospinal Fluid (CSF)

• Appearance (Color & Clarity)
  • Normal: Crystal clear and colorless, like a tube of water. Any deviation from this is significant
  • Cloudy/Turbid: Immediately suggests infection (meningitis). The cloudiness is caused by the presence of bacteria and the huge number of WBCs (primarily neutrophils) rushing in to fight it
  • Xanthochromia: This is a critical finding. It refers to a yellow, orange, or pinkish supernatant after centrifugation. It indicates that blood has been in the CSF for at least a couple of hours, signifying a subarachnoid hemorrhage, NOT a traumatic tap. In a traumatic tap, the supernatant will be clear
  • Bloody: How do we differentiate a traumatic tap from a true hemorrhage?
    1. Tube Comparison In a typical 3- or 4-tube collection, a traumatic tap will show decreasing amounts of blood from tube 1 to tube 3. In a hemorrhage, the blood will be evenly distributed in all tubes
    2. Clot Formation Traumatic taps may form clots due to the introduction of plasma fibrinogen. Pathologic CSF does not have enough fibrinogen to clot (with rare exceptions like TB meningitis, which can form a web-like pellicle)
    3. Centrifugation As mentioned, a spun sample from a hemorrhage will have a xanthochromic supernatant. A fresh traumatic tap will have a clear supernatant

Synovial Fluid (Joint Fluid)

• Appearance (Color & Clarity)
  • Normal: Pale yellow, straw-colored, and clear
  • Abnormal: Deeper yellow can indicate inflammation (non-inflammatory arthritis). A cloudy or turbid appearance points towards inflammatory conditions like Rheumatoid Arthritis (due to WBCs) or gout (due to crystals). A purulent, opaque fluid is highly indicative of a septic (bacterial) arthritis. A red/brown fluid indicates hemorrhage into the joint
• Viscosity: This is a hallmark test for synovial fluid!
  • Normal: The fluid is viscous (thick) due to a high concentration of hyaluronate. We test this with the “string test.” By aspirating the fluid into a pipette and dispensing it, a normal sample will form a string 4-6 cm long before breaking
  • Abnormal: In inflammatory conditions like RA, bacteria and inflammatory cells release enzymes that break down the hyaluronate. This causes the fluid to become watery, and the string test will be poor (short string or breaks immediately)

Serous Fluids (Pleural, Peritoneal, Pericardial)

• Appearance (Color & Clarity)
  • Normal: A small amount of pale yellow, clear fluid exists in these spaces for lubrication
  • Transudate vs. Exudate: The physical appearance is our first clue. Transudates are systemic effusions (e.g., from congestive heart failure) and are typically pale yellow and clear. Exudates are localized effusions (e.g., from infection or malignancy) and are often cloudy, turbid, or bloody due to the presence of cells and high protein
  • Bloody (Hemorrhagic): Indicates trauma or malignancy
  • Milky (Chylous/Pseudochylous): A milky white fluid can be a chylous effusion, caused by obstruction of the thoracic lymphatic duct, which is rich in triglycerides. A pseudochylous effusion looks similar but is typically seen in chronic inflammatory conditions like RA or TB and is rich in cholesterol

Amniotic Fluid

• Appearance (Color & Clarity)
  • Normal: Colorless to pale yellow. It can have some slight turbidity from fetal cells, hair, and vernix, which increases as the pregnancy progresses
  • Green: This is a significant finding and indicates the presence of meconium (the baby’s first stool), which suggests fetal distress
  • Yellow/Amber: Points to the presence of bilirubin, a key indicator of Hemolytic Disease of the Newborn (HDN)
  • Dark Red/Brown: Associated with fetal death

Semen

• Volume: A key fertility parameter. Normal is 2-5 mL
• Appearance: Normal is gray-white and opalescent. It can appear more clear with very low sperm counts. Red/brown indicates blood; yellow may indicate urine contamination or prolonged abstinence
• Liquefaction: After collection, semen is a coagulum. It must liquefy within 30-60 minutes at room temperature for the sperm to become motile. This process is due to prostatic enzymes. Failure to liquefy can indicate a prostate issue and cause infertility
• Viscosity: After liquefaction, normal semen should be able to be poured in discrete droplets. Highly viscous samples can interfere with sperm motility

Feces

• Color
  • Normal: Brown, due to the bacterial breakdown of bilirubin into urobilin/stercobilin
  • Black/Tarry: Indicates an upper GI bleed. The black color is from digested blood (oxidized iron)
  • Red: Indicates a lower GI bleed. The blood is fresh and has not been digested
  • Pale/Clay-Colored/Acholic: A classic sign of bile duct obstruction. Bilirubin can’t get into the gut to be converted to stercobilin, so the stool loses its color
  • Green: Can be caused by diet (leafy greens), certain medications, or rapid transit time where bile pigments don’t have time to be converted
• Consistency
  • Formed (Normal): Soft but holds its shape
  • Watery: Diarrhea, associated with infections or malabsorption
  • Bulky/Frothy/Greasy: Classic sign of steatorrhea, or fat malabsorption (e.g., in Cystic Fibrosis or Celiac Disease). These stools are often foul-smelling and may float

Putting It All Together

Never underestimate the power of simple observation. The physical examination is the first, and sometimes most important, chapter in the story of a patient’s sample. A “crystal clear” CSF can essentially rule out bacterial meningitis on the spot. A “watery” synovial fluid immediately points you towards an inflammatory process. And a “clay-colored” stool is a powerful clue pointing directly to the biliary system. This initial assessment isn’t just a formality; it’s a dynamic part of the diagnostic process that shapes the entire laboratory workup. Keep your eyes open