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CLS 1113 Introduction to Clinical Laboratory Practices

CLS 1113 Introduction to Clinical Laboratory Practices. Specific Gravity The Reagent Test Strip. Specific Gravity (Chapter 5&6). S.G. is a measure of the density (weight) of dissolved particles in the urine Assesses the kidney’s ability to reabsorb water and essential minerals

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CLS 1113 Introduction to Clinical Laboratory Practices

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  1. CLS 1113Introduction to Clinical Laboratory Practices Specific Gravity The Reagent Test Strip

  2. Specific Gravity (Chapter 5&6) • S.G. is a measure of the density (weight) of dissolved particles in the urine Assesses the kidney’s ability to reabsorb water and essential minerals • Also shows patient hydration • Weight of urine / Weight of water

  3. Specific Gravity • Normal range 1.005 to 1.025 • SG <1.002 or >1.040 are not physiologically possible • Measured by reagent test strip or refractometer

  4. Interference with SG tests • Glucose and Protein are actively REABSORBED in the nephron. • Their presence has nothing to do with the concentrating ability of the kidney. • If they are present in large amounts, they must be corrected for.

  5. For each gram/deciliter of protein subtract .003 from the specific gravity. • For each gram/deciliter of glucose subtract .004 from the specific gravity. • Example: • 2 gm/dl Glucose - .008 • 3 gm/dl Protein - .009 • Specific Gravity = 1.052 • Correction - .017 • Corrected SG = 1.035

  6. High S.G. dehydration high levels of glucose or protein x-ray contrast media or dye diabetes mellitus Low S.G. dilute urine renal failure tubular necrosis diabetes insipidus decreased ADH function Specific Gravity

  7. Urometer • Old Technology • Uses too much urine • Affected by large molecules in the urine • We don’t do it anymore!

  8. SG – Reagent Test Strip • Indirect colorimetric estimation of the specific gravity • Detects only the ionic solutes • No need to correct SG for glucose, etc. • Reagent Pad • Polyelectrolyte: pH indicator • Maintained at an alkaline pH • Immerse pad in urine the pKa of the polyelectrolyte will decrease with ionic concentration

  9. SG – Reagent Test Strip • Bromthymol Blue: indicator • As pH decreases color change • From dark blue-green (SG - 1.000) to yellow-green (SG - 1.030) • More ions – more protons released from polyelectrolyte – decrease pad pH – change in indicator.

  10. Osmolality • Is the concentration of a solution expressed in osmoles of solute particles per kilogram of solvent. • One osmole is the amount of a substance that dissociates to produce one mole (6.023 x 1023) of particles. NaCl(One mole of salt) Na+ Cl- (Two osmoles) Glucose (One mole) Glucose (One osmole)

  11. Osmolality • Performed by Freezing Point Depression. • The freezing point is inversely proportional to the concentration of the urine. • Dependant upon number of particles not size or ionic charge.

  12. Reagent Test Strip Reactions Based on three principles: 1.Colorimetric: substance in urine plus key color = visible reaction 2.Enzymatic: enzymes breakdown specific compounds = visible reaction 3.Catalytic: substance in urine causes reaction to proceed = visible reaction

  13. Reagent Test Strips Two different types of information result: 1.Qualitative: positive or negative 2.Quantitative: how much (mg/dl, 4 plus, etc.)

  14. Reagent Test Strips • Run a positive and negative control daily • Record results • Repeat if controls are out of range • Date bottles when received and when in use • QC new Lot #’s of reagents and strips

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