Urinalysis (Macroscopic Physical Tests) Urinalysis. Basic Urinalysis 12/22/2012. Mohammad Reza Bakhtiari DCLS, PhD

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1 Urinalysis (Macroscopic Physical Tests) Mohammad Reza Bakhtiari DCLS, PhD Urinalysis Basic Urinalysis CLSI: U/A is the testing of urine with procedures commonly performed in an expeditious, reliable, accurate, safe, and cost-effective manner. 1

2 Types of Urine Specimens Changes in Unpreserved Urine Renal Concentration 2

3 Specific Gravity The reabsorption process is often the first renal function to become impaired; therefore, an assessment of the kidney s ability to reabsorb is a necessary component of the routine urinalysis. This evaluation can be performed by measuring the specific gravity of the specimen. Specific gravity = ρ/ρ DW at a similar temperature. Other uses To detect possible dehydration To detect abnormalities in antidiuretic hormone To determine whether specimen concentration is adequate to ensure the accuracy of chemical tests. Specific Gravity vs. Osmolarity Specific Gravity A function of particles number & Size. Sensitivity to Glucose> Urea > Cl - > Na + A Screening Test. The specific gravity of the plasma filtrate entering the glomerulus is Normal random specimens may range from to 1.035, depending on the patient s amount of hydration. Most random specimens fall between and Osmolarity A function of particles number. Sensitivity to Ions (Na +, Cl -, ) = Others A quantitative measurement of renal concentrating ability An osmole is defined as 1 g molecular weight of a substance divided by the number of particles into which it dissociates. Clinical laboratory instruments are available to measure freezing point depression and vapor pressure depression. The effect of Hydration on Renal Concentration 3

4 SG Methodology Direct Urinometer (hydrometer) Harmonic Oscillation Densitometry (HOD) Indirect Refractometer Chemical reagent strip Urinometer The additional mass provided by the dissolved substances in urine causes the float to displace a volume of urine smaller than that of distilled water. Requires a large volume (10 to 15 ml) of specimen. The reading may need to be corrected for temperature, If the specimen is cold, / 3 C that the specimen temperature is below the urinometer calibration temperature. Conversely, / 3 C that the specimen measures above the calibration temperature. A correction also must be calculated when using either the urinometer or the refractometer if large amounts of glucose or protein are present. For each gram of protein present, For each gram of glucose present, Dilution Procedure Refractometer Refractive index is a comparison of the velocity of light in air with the velocity of light in a solution. The concentration of dissolved particles present in the solution determines the velocity and angle at which light passes through a solution. Requires a small volume of specimen. Temperature corrections are not necessary (15-38 C). Corrections for glucose and protein are still calculated, although refractometer readings are less affected by particle density than are urinometer readings. Calibration 4

5 Refractometer Calibration Calibration of the refractometer is performed using distilled water that should read If necessary, the instrument contains a zero set screw to adjust the distilled water reading. The calibration is further checked using 5% NaCl, which should read ±0.001, or 9% sucrose that should read ± Urine control samples representing low, medium, and high concentrations should also be run at he beginning of each shift. Calibration and control results are always recorded in the appropriate quality control records. Strip Specific Gravity A convenient method for routine screening. Based on the change in pka (dissociation constant) of a polyelectrolyte in an alkaline medium. As the specific gravity increases, the indicator changes from blue (1.000 [alkaline]), through shades of green, to yellow (1.030 [acid]). Readings can be made in intervals by careful comparison with the color chart. Replacing osmometry or refractometry for critical fluid monitoring is not recommended. Strip Specific Gravity The reagent strip specific gravity measures only ionic solutes, thereby eliminating the interference by the large organic molecules, such as urea and glucose, and by radiographic contrast media and plasma expanders that are included in physical measurements of specific gravity. FP results: Elevated concentrations of protein slightly increase the readings as a result of protein anions. FN results: Specimens with a ph 6.5 have readings caused by interference with the bromthymol blue indicator. Therefore, manufacturers recommend adding to specific gravity readings when the ph 6.5.The correction is performed by automated strip readers. 5

6 Color & Appearance Color and Clarity Procedure Clarity Terminology Appearance Non Pathologic Causes of Urine Turbidity Pathologic Causes of Urine Turbidity Laboratory Correlations in Urine Turbidity 6

7 Laboratory Correlation of Urine Color Laboratory Correlation of Urine Color Common causes of Urine Odor 7