14.3 Microscopy Parts, Magnification, Wet Prep, and Cleaning

AMT III.9.C requires microscopy terminology, microscopic urinalysis procedures within the laboratory assistant’s scope, and general cleaning of the microscope. III.9.B.2 adds prepare slides for microscopic examination. CLIA provider-performed microscopy (PPM) (42 CFR 493.19) is a moderate-complexity subset restricted to providers. A CMLA may prepare slides and perform sediment microscopy only when the laboratory’s certificate, SOP, and competency checklist authorize that assistant-level work. A CMLA must not independently sign out PPM procedures.

Quick Answer: Total magnification = ocular × objective. A typical ocular is 10×. Scan casts on 10×; count cells on 40× high dry. Immersion oil belongs only on the 100× oil objective—never on 40×. Light travels lamp → diaphragm → condenser → specimen on the stage → objective → ocular. PPM (wet mounts, KOH, fern, pinworm, and the rest of the federal list) is provider work. Clean optics with lens paper; wipe oil off the same day.

Parts you must name

AMT’s outline spells “fine/course.” The knob is coarse (large movements), not “course work.” Exam stems may use either spelling; the function does not change.

Total magnification = ocular × objective. 10× ocular × 10× objective = 100×. 10× × 40× = 400×. 10× × 100× = 1000×. You do not add the numbers (10 + 40 is not 50×), and you do not oil a 40× lens “to get 1000.”

Light path

Light is born in the base, shaped by the diaphragm, focused by the condenser onto the specimen on the stage, collected by the objective, and magnified again by the ocular. If the field is dark, check the lamp, the diaphragm, the condenser height, and whether an objective is clicked in—before you twist coarse adjustment through the slide.

Prepare a urine sediment slide (assistant scope)

Follow the laboratory SOP. Classic manual teaching (volumes and g-force are SOP numbers, not improvisation):

1. Mix the specimen. Pour a measured volume (often about 12 mL) into a labeled centrifuge tube.
2. Centrifuge at the SOP relative centrifugal force and time (classic teaching is about 400–450 × g for 5 minutes). Too hard packs casts into a button you then dump; too light leaves cells in the supernatant.
3. Decant or pipette off supernatant, leaving a uniform small residual volume. Do not drain dry and then “add a drop of water to save it.”
4. Gently resuspend the button. Place one drop on a labeled slide and add a coverslip for a wet preparation. Avoid bubbles (artifacts).
5. Optional supravital stains (for example Sternheimer-Malbin) only if the SOP uses them. Do not invent a Gram stain on a UA cup and call it C&S.
6. Examine sooner rather than later. Casts dissolve in alkaline dilute urine; trichomonas motility fades; bacteria multiply in delayed unpreserved sediment.

What you look at, at which power:

• 10× objective (100× total): scan the entire coverslip for casts, large crystals, mucus, and to find a representative area. Casts are easy to miss if you jump straight to 40× in one corner.
• 40× objective (400× total): identify and count cells, bacteria, yeast, crystals, trichomonas, and spermatozoa. This is high-dry. No oil.
• 100× oil: not the routine UA counting objective. Oil is for stained smears (Gram stain is Chapter 13), not for a wet coverslip you still need to scan on 40×.

Brightfield is the default teaching method. Some laboratories use phase contrast for hyaline casts. Use what the SOP validates. Report using the laboratory’s format (cells per high-power field, casts per low-power field). Do not upgrade a wet drop into a species-level microbiology identification.

PPM is not a CMLA sign-out category

Provider-performed microscopy is moderate-complexity testing that CLIA allows certain licensed providers to perform under a PPM certificate (42 CFR 493.19). AMT IV.11.A.6 states the same restriction: PPM is providers only. The federal PPM procedure list includes:

• Direct wet mounts (bacteria, fungi, parasites, cellular elements)
• KOH preparations
• Pinworm examinations
• Fern tests
• Post-coital mucus examinations
• Urine sediment examinations when performed as PPM
• Nasal smears for granulocytes
• Fecal leukocyte examinations
• Limited qualitative semen analysis (presence or absence of sperm and motility)

A CMLA does not independently perform or sign out PPM procedures because “I can use a microscope.” Wet mounts, KOH, fern, and pinworm are the favorite exam names.

Separate idea: a laboratory with a Certificate of Compliance or Accreditation may assign manual urine microscopy to testing personnel who are trained, competency-assessed, and listed in the SOP. That is still not a personal PPM license. If you are in a Certificate of Waiver site, manual sediment microscopy is not a waived dipstick. Do not turn a closet microscope into an uncertified moderate-complexity department.

You may prepare the slide for a provider or a qualified analyst. Preparing is not signing the report.

General cleaning

• Switch to 10×, lower the stage, remove the slide.
• Oil: wipe 100× with lens paper immediately after use. Do not leave oil overnight. Never drag the 40× objective through leftover oil when you spin the nosepiece.
• Optics: lens paper (or manufacturer wipes). Facial tissue and paper towels scratch coatings. A tiny amount of manufacturer-approved lens cleaner if SOP allows—not alcohol dumped on the ocular, not a xylene bath you invented.
• Stage and base: disinfectant compatible with the instrument after a urine splash. Do not soak the electrical housing.
• Cover the microscope. Carry it with two hands (base and arm), never by the oculars.
• Do not use coarse adjustment as a bottle opener. Document lamp failures and damaged objectives instead of “making do.”

In practice

A waived clinic wants you to “just KOH that discharge and fern that mucus” because the microscope is already on. Those are PPM procedures. You do not independently examine or sign them, and you route the request to a provider credentialed for PPM or to the main laboratory. For a hospital UA with micro that your competency list includes, you spin the measured aliquot, coverslip a wet drop, scan on 10× for casts, identify on 40×, never oil the 40×, and clean the 100× only if you actually used it for a stained smear elsewhere.

Exam traps

• Adding 10 + 40 = 50×, or oiling 40× to “get 100×.”
• Coarse-focusing on high power through the slide.
• Calling wet mount, KOH, fern, or pinworm CMLA-independent work.
• Reporting unspun urine as a complete microscopic.
• Cleaning optics with gauze, or leaving oil on the 100× so the 40× wades through it tomorrow.

Name the part, multiply the lenses, keep oil on 100×, and keep PPM on the provider’s side of the line.