MLP II Unit 4: Chemistry

POC tests in the medical office

• Glucose

• A1C

• Cholesterol

Blood chemistry

• Quantitative measurement of chemical substances in the plasma

POCT Chemistry Analyzers

• Accu-Check glucometers

• A1c Now (for HgA1c)

• Cholestetech LDX Cholesterol System

• Each machine has an operating manual, personnel for on-site training, and sometimes instructional DVDs to help the staff using them

• It is important to learn your analyzers b/c improper use causes false results!

Quality Control

• The goal of chem testing is to obtain ACCURATE results!

• We can guarantee accuracy through QC

• Two methods of QC: calibration and controls

Controls

• A control is a solution similar to patient sample with a known result — usually an acceptable range

• We use this to determine if reagents are performing properly

• We also use to detect errors in technique by person performing test

• Two levels:

  • Low/normal AKA level 1

  • High AKA level 2

When controls don’t work

• Expired reagents/strips

• Improper storage

• Errors in technique used to perform test

• Cannot run patient samples until controls work

• According to CLIA, controls should be performed each day the test is done on a patient sample

Calibration

• Used to check precision & accuracy of machine

• Detects errors caused by lab equipment not working properly

• Performed using a standard — usually a strip or cassette inserted in analyzer

  • Standards have EXACT known measurements — not an acceptable range like QC

• If results are what we expect them to be, machine is in good condition

• If not, patient samples shouldn’t be run until issue is fixed

• Calibration frequency should be at least every 6 month according to CLIA

  • Usually at least when you use a new lot number

Glucose

• Glucose is the end product of carb metabolism, required for energy

• Ingested glucose not needed is stored as glycogen in muscle and liver

• When no more tissue storage is possible, it is converted to triglycerides and stored as adipose tissue

• Insulin is a hormone secreted in pancreas required for normal use of glucose in body

• Needed to convert glucose to energy and also to glycogen

• Normal glucose levels are necessary for homeostasis

• Diabetes is the most common disease that affects glucose levels

• Other diseases:

  • Pancreatitis

  • Endocrine disorders

  • Chronic renal failure

Type 1 Diabetes

• AKA juvenile diabetes

• Inherited disorder, usually presents before 18

• Autoimmune disease — body attacks beta cells of the pancreas

• When beta cells are 80% destroyed, pancreas does not secrete enough or any insulin to manage blood glucose levels

• No way to prevent

• Tx is insulin injections or insulin pump

Type 2 Diabetes

• Adult-onset, lifestyle related

• Insulin is available but not used correctly by the body

• Treatments are lifestyle changes, oral medication, only insulin shots when other treatments don’t work

• Both types of diabetes can cause serious complications with nerves, kidneys, eyes, circulation, and more

Diabetes S&S

• Elevated fasting blood glucose (>140 mg/dL)

• Polyuria

• Polydipsia

• Blurred vision

• Positive glucose & ketones on UA dipstick

Fasting Blood Glucose

• Normal FBG is 70-100 mg/dL

• Fasting = 10-14 hours with nothing to eat or drink (only water)

• This can be a POC test, done on glucometer with capillary blood (or venipuncture, analyze plasma)

  • As with all CLIA tests, you must perform normal and abnormal controls on each day of use & they must work!

  • Check lot numbers and expiration dates on strips & controls, make sure to use the same brand of strips as your glucometer

• If FBG is elevated, provider can order a glucose tolerance test (GTT)

• Provider usually makes diagnosis based on two or more elevated FBG results and results of GTT

3 Hour Glucose Tolerance Test

1. Draw FBG when patient arrives — if too high, physician may not continue test

2. Give patient oral glucose drink (usually contains 100 g of glucose)

3. Instruct patient they have 5 minutes to drink it, bring bottle up when finished

4. When the patient is finished with the drink, start timer for 1 hour

5. At 1 hour, draw patient’s blood then set timer for another hour

   1. After 1 hr, blood glucose should be 139 mg/dL or less

6. At 2 hours, draw patient’s blood then set another 1 hour timer

7. At 3 hours, draw patient’s blood and let patient leave

8. During the test, patients cannot walk around, smoke, or eat

9. Provider will look at glucose results from all three draws to determine glucose tolerance

10. This is often done on pregnant women who fail the 1 hour GTT to diagnose gestational diabetes!

HgA1C

• Used to monitor average glucose levels over a three month period — gives more in depth look rather than one FBG

• Measuring the amount of sugar that has absorbed on the RBC membrane

• Performed no more frequently than every 3 months — remember the average lifespan of an RBC is about 120 days

• For diabetic patients, the goal is to have HgA1C below 7%

• Non-diabetic should be 4-6%

• CLIA-waived test uses capillary blood, quick and easy

Cholesterol

• Waxy, fat (lipid) essential for body functions

• Essential for cell membranes and production of hormones and bile

• Most produced by liver, but some comes from diet

• Amount of cholesterol affected by genetics and consumption of fat

  • Can cause atherosclerosis — build up of fatty plaque on walls of arteries

  • Can lead to heart attack, stroke, coronary artery disease

  • Hypothyroidism can also cause elevated cholesterol!

LDL

• Picks up cholesterol from liver and ingested fats and deposits in blood vessels

• This causes atherosclerosis

• “Bad” or “Lousy” cholesterol

HDL

• Removes excess cholesterol from cells/blood vessels and carries to liver to be removed

• Lowers cholesterol buildup in arteries, reduces risk for CAD

• “Good” or “Healthy” cholesterol

• Ideal is greater than 60 mg/dL

• Men - <40 and women - <50 = greater risk for heart disease

Cholesterol testing

• All adults over 20 should have a total cholesterol tested once every 5 years

• Cholesterol tests are screening tools to see if patient is at risk for CAD

• Total cholesterol should be below 200 mg/dL

• HDL is also measured, because low HDL increases risk for CAD

• LDL is a calculation of HDL and total cholesterol

• Patients do not need to fast for this test

Triglycerides

• Fat in the blood related to caloric intake

• Elevated levels typically stored in belly, associated with central obesity

• Comes from two sources

  • Glucose

  • Diet

• Normal range is below 150 mg/dL

• If triglycerides are consistently elevated it suggests greater risk for CAD

• Patients DO need to be fasting for this test!

• Conditions with elevated triglycerides:

  • Obesity

  • Type 2 diabetes

  • Physical inactivity

  • Excessive alcohol consumption

  • Smoking

  • Hypothyroidism

  • Kidney disease

  • Liver disease

Thyroid testing

• Thyroid located in anterior neck, produces T3 and T4

  • Primary hyper/hypothyroidism

• Pituitary gland in brain controls thyroid by secreting thyroid stimulating hormone or TSH

  • Secondary hyper/hypothyroidism

• Hypothalamus in brain controls this entire process by secreting thyroid regulating hormone or TRH

  • Tertiary hyper/hypothyroidism

• Deficiencies in this process are called hypothyroidism (underactive thyroid) or hyperthyroidism (overactive thyroid) and can be caused by genetics or autoimmune diseases

Hypothyroidism

• Underactive thyroid

• Genetics or autoimmune

  • Autoimmune = Hashimoto’s

• S&S

  • Weight gain

  • Fatigue

  • Dry skin

  • MANY more!

Hyperthyroidism

• Overactive thyroid

• Genetics or autoimmune

  • Autoimmune = Graves disease

• S&S

  • Weight loss

  • Exophthalmos

  • Cardiac arrhythmias

  • Menstrual irregularities

  • Sleep problems

  • MANY more!

Kidney function tests

• Blood Urea Nitrogen (BUN)

  • Urea is the end product of protein metabolism

  • Normally present in blood and eventually excreted by kidneys

  • Problems with kidney usually = elevated urea (BUN)

• Creatinine

  • A waste product of creatine phosphate (muscles)

  • Elevated in kidney problems

Commonly measured electrolytes

• Sodium (Na) — conditions r/t = hypernatremia, hyponatremia

• Potassium (K) — conditions r/t = hyperkalemia, hypokalemia

  • Falsely elevated in hemolyzed samples!!

• Chloride

• CO2

Panels

• Physicians often order panels as part of physical or to diagnose disease:

  • Basic Metabolic Profile (BMP)

  • Comprehensive Metabolic Profile (CMP)

  • Renal Function Panel

  • Liver Function Panel

  • Lipid Panel

Basic Metabolic Profile (BMP)

• Most common chemistry test ordered

• Tests:

  • Glucose

  • Calcium

  • Electrolytes

  • Kidney function (BUN, Creatinine)

• Used for screening or to monitor kidney function, diabetes management

Comprehensive Metabolic Profile (CMP)

• Also commonly ordered

• More in-depth than BMP because it measures protein and liver function

• Tests:

  • Glucose

  • Calcium

  • Electrolytes

  • Protein

  • Kidney tests: BUN/Creatinine

  • Liver tests: ALT, AST, bilirubin, ALP

Renal Function Panel

• BUN

• Creatinine

• Uric acid

• Glucose

Liver Function Panel

• ALP

• GGT (liver specific enzyme, elevated in cirrhosis, severe liver damage)

• AST

• ALT

• LDH

• Bilirubin — can monitor separately in newborns

• Helpful diagnosing and monitoring liver disease, more in-depth than CMP!

Thyroid Panel

• T3

• T4

• TSH

Medication testing

• Trough — medication level drawn before patient is to take his/her dose

• Peak — medication level drawn 30 minutes after a dose of the medication

Specimen Collection Errors

• Hemolysis

• Exposure to light

• Centrifugation

• Drawing the wrong tube

Hemolysis

• Small needle, pulling too hard on syringe

• Causes many errors in results, ESPECIALLY POTASSIUM (falsely increased)

Exposure to light

• Light breaks down bilirubin, causes falsely decreased bilirubin

Centrifugation

• Not centrifuging promptly can cause intracellular RBC material to leach out into serum (falsely elevated potassium)

Drawing the wrong tube

• Usually we draw a green tube for chemistry, but some tests require serum tubes or other special tubes