Urinalysis: Specific Gravity Calculation

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Questions and Answers

What is the correction factor for glucose in specific gravity measurement?

0.003 for every g/dL glucose

0.005 for every g/dL glucose

0.004 for every g/dL glucose (correct)

0.001 for every g/dL glucose

What is the purpose of the motion detector in the U-shaped glass tube?

To apply electric current to the coil

To amplify the electric current

To detect the sound wave frequency (correct)

To measure the velocity of the sound wave

What is the calibration temperature usually printed on the instrument?

30°C

25°C

35°C

20°C (correct)

How does the microprocessor convert the reading to specific gravity?

By converting the change in sound wave frequency Signup and view all the answers

What is the refractive index a comparison of?

The velocity of light in air and in the urine sample Signup and view all the answers

What is the correction factor for protein in specific gravity measurement?

0.003 for every g/dL protein Signup and view all the answers

What is the purpose of electric current in the U-shaped glass tube?

To generate a sound wave in the urine sample Signup and view all the answers

What is the correction factor for temperature in specific gravity measurement?

Deduct 0.001 for every 3°C above the calibration temperature Signup and view all the answers

Which of the following is the purpose of cytodiagnostic urine testing?

To provide definitive information about renal tubular changes associated with transplant rejection Signup and view all the answers

Why is it recommended to use reduced light when examining unstained sediment by bright-field microscope?

To reduce glare from the microscope Signup and view all the answers

What is the purpose of reporting the microscopic examination of urine?

To provide consistent results within a laboratory system Signup and view all the answers

What type of stain is used for slides prepared by cytocentrifugation?

Papanicolaou stain Signup and view all the answers

What is the first step in the formation of bilirubin?

Hemoglobin breakdown into heme Signup and view all the answers

What is the purpose of scanning the cover-slip perimeter under LPO?

To examine hemosiderin-containing cells and casts Signup and view all the answers

What is the role of the urinalysis laboratory in cases with unusual cellular findings?

To refer specimens to the cytology laboratory for further examination Signup and view all the answers

What is the role of glucoronic acid in bilirubin formation?

Conjugation with bilirubin Signup and view all the answers

What is the purpose of converting the number of elements per LPF or HPF to the number per mL?

To provide standardization Signup and view all the answers

What is the purpose of the reagent peroxide in the blood reagent strip?

To oxidize the chromogen Signup and view all the answers

What is the clinical significance of conjugated bilirubin in the urine?

It is an indicator of liver disease Signup and view all the answers

What is the term used to describe the number of RBCs and WBCs observed under the microscope?

Semiquantitative terms Signup and view all the answers

What is the purpose of the reagent tetramethylbenzidine in the blood reagent strip?

To act as a chromogen Signup and view all the answers

What is the result of bilirubin formation in the intestines?

Formation of urobilinogen Signup and view all the answers

What is the significance of bilirubinuria in liver disease?

It is an early indicator of liver disease Signup and view all the answers

What is the result of intact RBCs on the pad in the blood reagent strip?

Formation of a speckled pattern Signup and view all the answers

What is the primary function of the oculars/eyepiece lens?

To further magnify and concentrate light into the specimen Signup and view all the answers

What is the purpose of the Abbe condenser?

To optimize light quality and sharpness Signup and view all the answers

What is the function of the iris diaphragm?

To control the amount of light passing through the specimen Signup and view all the answers

What is the purpose of the field diaphragm?

To focus the light onto the stage Signup and view all the answers

What is the main purpose of Kohler illumination?

To optimize light quality and sharpness Signup and view all the answers

What happens to the image in the microscope?

It appears upside down and reversed Signup and view all the answers

When is Kohler illumination performed?

Whenever an objective is changed Signup and view all the answers

What is the purpose of the objectives in the lens system?

To perform the initial magnification Signup and view all the answers

What is the purpose of adding 0.005 to specific gravity readings when the pH is 6.5 or higher?

To correct for the automated strip reader's error Signup and view all the answers

What is the reagent used in urine tests for ascorbic acid?

Methylene green Signup and view all the answers

What is the minimum amount of ascorbic acid detectable by C-Stix at 60 seconds?

25 mg/dL Signup and view all the answers

What is the significance of a urine test showing 150 mg/dL of ascorbic acid?

Adequate ascorbic acid therapy Signup and view all the answers

What is the purpose of microscopic examination of urine?

To identify and quantify insoluble materials in urine Signup and view all the answers

What is the significance of a urine test showing a color change from blue to purple?

Presence of ascorbic acid Signup and view all the answers

What is the role of neutral red in urine tests for ascorbic acid?

It provides a background color Signup and view all the answers

What is the correlation between the clarity of urine and the presence of hematuria?

Cloudy urine indicates the presence of hematuria Signup and view all the answers

Study Notes

Urinalysis

Specific gravity measures the ability of the kidneys to reabsorb essential chemicals and water.
For every g/dL of CHON, deduct 0.003 from the specific gravity reading.
For every g/dL of glucose, deduct 0.004 from the specific gravity reading.
For every 3°C drop in calibration temperature, deduct 0.001 from the specific gravity reading.
For every 3°C above the calibration temperature, add 0.001 to the specific gravity reading.
Calibration temperature is usually 20°C.

Clinical Microscopy

Refractometry measures specific gravity by measuring the refractive index.
Refractive index is a comparison of the velocity of sound waves in air and in the urine sample.
Electric current is applied to the coil, causing a sound wave to pass through the urine sample.
The microprocessor measures the change in sound wave frequency and converts it to specific gravity.

Blood Reagent Strip

Pseudoperoxidase activity of hemoglobin is the principle of the blood reagent strip.
Reagents used are peroxide, tetramethylbenzidine, and buffer.
Reaction: H2O2 + chromogen –Hgb Peroxidase→ oxidized chromogen (yellow to green to blue color*) + H2O.
Sensitivity: Multistix (5-20 RBCs/mL, 0.015-0.062 mg/dL hgb), Chemstrip (5 RBCs/mL, hgb corresponding to 10 RBCs/mL).
Correlation with other tests: protein, microscopic examination.

Bilirubin

Formation of bilirubin: RES (RBC → hgb → heme → protoporphyrin → biliverdin → B1) → circulation (B1 coupled with albumin) → liver (B1 conjugated with glucoronic acid to form B2) → intestines (B2 converted to urobilinogen by intestinal bacteria).
Clinical significance of bilirubinuria: early indicator of liver disease, conjugated bilirubin appears in urine when there is bile duct obstruction or liver damage.
Used in determining the cause of jaundice.

Ascorbic Acid

Urine tests for ascorbic acid have been used as an indication of adequate ascorbic acid therapy.
Large quantities of ascorbic acid may occasionally be found in the urine of individuals taking therapeutic doses of vitamin C or other preparations containing ascorbic acid.
Reagent: methylene green, which is reduced to its colorless form with ascorbic acid.
Neutral red provides a background color, and the overall color changes from blue to purple at levels of 150 mg/dL.

Microscopic Examination of Urine

Used to detect and identify insoluble materials in urine.
Must include quantitation of elements present.
Some elements are considered normal unless present in increased amounts.
Slide examined first under LPO, setting changed to HPO for identification.
LPO scanning of cover-slip perimeter is recommended.
For detection of casts, use reduced light when examining unstained sediment by bright-field microscope.

Reporting the Microscopic Examination

May vary among laboratories but must be consistent within a particular laboratory system.
Routine reporting includes:
- Casts: per 10 LPFs.
- RBCs and WBCs: per 10 HPFs.
- Epithelial cells, crystals, and other elements: semi-quantitative terms (rare, few, moderate, many).

Oculars/Eyepiece Lens

Responsible for further magnification and resolution (ability to visualize fine details).
Coarse- and fine-adjustment knobs.
Iris diaphragm: controls the amount of light that will pass through the specimen.
Rheostat: controls the intensity of light.
Image in the microscope is upside down and reversed.

Microscopy

Kohler illumination is a technique to optimize light quality and sharpness by aligning and adjusting each component of the optical system.
Adjustments done to provide optimal viewing of illuminated objects.
Steps:
- Place a slide on the stage and focus using LPO with the condensers raised.
- ...

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Description

This quiz covers the calculations involved in determining specific gravity in urinalysis, including the effects of glucose and temperature on specific gravity measurements.