Activity 1.3
Measuring Specific Gravity: The Refractometer Method

Materials and Equipment

• Gloves
  
  
• Hand disinfectant
  
  
• Puncture-proof container for sharps
  
  
• Clear plastic conical centrifuge tubes
  
  
• Test tube rack
  
  
• Fresh urine sample
  
  
• Dropping pipet
  
  
• Refractometer
  
  
• Distilled water
  
  
• Urinalysis report form or worksheet
  
  
• Soft tissue or soft paper towels
  
  
• Biohazard container
  
  
• 10% chlorine bleach solution or other surface disinfectant
  
  
• Urine control solutions

Procedure

1. Wash hands and put on gloves.
   
   
2. Assemble equipment and materials.
   
   
3. Obtain a fresh urine specimen. If specimen has been refrigerated, allow it to reach room temperature before proceeding with tests.
   
   
4. Record the specimen identification on the worksheet (or report form).
   
   
5. Mix the urine gently by swirling and pour approximately 10 mL into a clear, conical centrifuge tube.
   
   
6. Place one drop of distilled water on the glass plate of the refractometer and close gently.
   
   
7. Look through ocular and read the specific gravity from the scale. For water, the specific gravity should read 1.000. (If it does not, calibrate with the screwdriver provided with the refractometer).
   
   
8. Wipe the water from the glass plate, place one drop of urine control solution on the plate and close gently.
   
   
9. Look through the ocular, read the specific gravity from the scale, and record the control value.
   
   
10. Clean the glass plate with disinfectant and dry with a soft tissue.
    
    
11. Repeat steps 8-9 with a urine specimen(s), recording result(s).
    
    
12. Discard urine sample(s) properly.
    
    
13. Disinfect and clean equipment and return to proper storage.
    
    
14. Clean work area with disinfectant.
    
    
15. Remove and discard gloves appropriately.
    
    
16. Wash hands with hand disinfectant.