Lecture 6-Quality Contro

Quality Control

A process in which the actions of people, performance of equipment and materials ensure the reliability of analytical test results

How are Q.C accomplished

• with the use of

• standards,

• controls

• and statistical analysis

• Involve running controls, check for accuracy and precision, controls within ± 2SD

Standard Deviation (SD)

• ◦ Refers to the natural variation (or random dispersion) of data points about the mean that will exist in any series of data

• ◦ SD is always expressed as a plus or minus (±) from the mean

• ◦ Used in the laboratory to define the limits that will allow any measurement to vary e.g. to establish normal ranges

  •  Normal range

  • – the limits within which a result can vary and still be considered normal

Laboratories to establish the allowable SD for each analytical method

confidence limit

Two standard deviation from the mean includes 95% of all values

A ± 2 SD limit is commonly used to accept or reject control values

If control results are outside ± 2 SD, patient samples cannot be tested

– troubleshoot and fix the problem

Used with Levy-Jennings Chart

Automated Testing Instrumentation could include

• Patient home use

  • ◦ Blood glucose meters

• Physician’s Office

  • ◦ Hb / Hgb

  • ◦ Urine dipstick

  • ◦ Blood glucose

Point-of-Care Testing (POCT)

• ◦ Critical care areas in the hospital

  •  Emergency department, ICU, OR …

• ◦ Test most often done at the patient’s bedside

  •  Blood glucose, electrolytes, cardiac markers

• ◦ Portable analyzers that give rapid, reliable test results

  • – decreasing TAT

• ◦ Usually require a very small amount of blood (one or two drops of capillary blood)

benefits of POCT in Hospitals / Private Labs

◦ High volume testing

◦ Capable of performing a variety of tests

◦ Less variation in technique

◦ Capable of producing accurate results

◦ Shorter TAT - Improved rate of diagnosis and treatment

◦ Laboratories are required to run controls for each test performed

◦ Controls must fall within ± 2SD

Principles of Instrumentation

Patient samples applied to individual cartridge, cassette or reagent strip for reactions

Instrument detect and quantitate the endpoint of the reaction – samples and reagents

Principles include:

◦ Photometry / Spectrophotometry (A / %T)

◦ Ion-Selective Electrodes (pH - H+, Na, K, Cl ...)

◦ Electrochemical Technology (glucose meters)

Blood collection chemistry tests : Venous or capillary

 Serum most often used (SST)

• avoid glass, as it is a clot activator'

• serum ideal for alot of test, but must wait 10 mins till blood has clotted, then spin down

 Could also include plasma (heparinized) or whole blood

• plasma has faster TAT

• usually use Lithium avoid sodium heparin

• not great for all tests

Serum is commonly used for most clinical chemistry tests

Depending on the analyzer and methods, serum, plasma and/or whole blood may be used

Be familiar with all blood collection tubes and anticoagulants

◦ Chemistry – SST, red top, green, grey, royal blue

Blood collection chemistry tests :Arterial

 For blood gas measurements – Heparinized sample

 Place on ice and analyze immediately

Body fluids for chemical testing

• Urine,

• CSF,

• pleural,

• synovial,

• pericardial

• and amniotic fluids

Blood and Urine – most commonly tested in Clinical Chemistry laboratory

Collection of blood specimen

Avoid collecting blood from an arm with IV, or collecting above an IV line

Specimen must be free from hemolysis

◦ Falsely elevated results – K+, LD, AST, Mg+, Iron, Vitamin B12, Folate

Timing of specimen – fasting

Avoid delay in delivery to the lab or testing – test within one hour of collection

◦ Refrigerate at 40C if testing is delayed

Proper centrifugation is essential

Analyte

Chemical substance for analysis

Profiles

Group of tests performed to determine the condition of patients, function of tissues or systems

include –

• Kidney/renal,

• liver/hepatic,

• cardiac,

• lipid,

• thyroid

Units of measurement – SI units of Analytes

millimoles per liter – mmol/L

Units of measurement – SI units of Enzymes

Units per liter – U/L

or international units IU/L

Units of measurement – SI units of Therapeutic Drugs

often in mg/dL (mol/L)

Electrolytes / “Lytes”

Electrolytes – ions in body fluids

Measurement of electrolytes include:

◦ Na+, K+, Cl-, HCO3-

◦ Cations and Anions

Electrolyte balance within the body is important in maintaining fluid and acid-base balance

Electrolyte imbalance affect all organs and body systems – can be life-threatening

Influence:

Blood volume

Blood pressure

Fluid retention

Muscular activity

Blood pH

INTRACELLULAR ELECTROLYTES

• POTASSIUM

• MAGNESIUM

• PHOSPHOROUS

Electrolyte measurement can be done on laboratory instruments or as POCT

EXTRACELLULAR ELECTROLYTES

• SODIUM & CALCIUM

• CHLORIDE

• BICARBONATE

Hypernatremia (sodium electrolytes)

◦ Excess loss of H2O or excessive retention of Na

 Dehydration

 Diabetes Insipidus

Hyponatremia (sodium electrolytes)

◦ Excessive sodium loss or H2O gain

 Diabetic acidosis

 Renal diseases

Sodium Functions

Transmission of nerve impulses

Regulation of body fluid levels

Assists with regulation of acid-base balance by combining with Cl or HCO3 to regulate the balance

Potassium

is the most abundant cation in the body cells

97% is found in the intracellular fluid

If Serum is left sitting on a blood clot the potassium will leak out of the cells, causing the potassium level in the serum to increase

• cell lysis

A serum K+ level below 2.5 or above 7.0 mmol/L can cause cardiac arrest

• but reference values varry depending on organization

80-90% is excreted through the kidneys

Potassium Function (has Na and K have similar dysfunction)

◦ Promote transmission of nerve impulses

◦ Regulate heartbeat and muscle function

◦ Promote enzyme action

◦ Assist in the maintenance of acid-basex

Hyperkalemia (potassium electrolyte)

– Results from impaired renal function

 Anoxia

 Acidosis

Hypokalemia (potassium electrolyte)

– Prolonged diuretic therapy(loss of water)

 Inadequate intake of potassium

 Increase aldosterone

less potassium, less H2O

Chloride

Maintain serum osmolarity

Works with Na in retention of water

Assist with regulation of acid-base balance

Combine with other ions for homeostasis

◦ Cl combines with hydrogen to form hydrochloric acid in the stomach

Increased Cl-:

dehydration and respiratory difficulties (hyperventilation)

Decreased Cl-:

renal diseases

Bicarbonate

Helps to maintain blood pH (very important process)

Usually measured as total CO2

Changed by respiration

◦ Diabetic/Ketoacidosis

◦ Renal failure

Calcium (Ca)

Necessary for proper bone and teeth development, blood coagulation

Highest concentration of minerals in the body

Vitamin D is necessary for the absorption and use of calcium

• Reference Range 1.15 – 1.33 mmol/L

Hypercalcemia

causes – Parathyroidism, kidneystones …

Hypocalcemia

– Life threatening – Vitamin D3 deficiency, impaired absorption, kidney disease …

Phosphorus / Phosphate

Necessary for proper bone and teeth development and cell membrane

High energy compounds (ATP) within cells

Reference Range 0.96 – 1.44 mmol/L

Magnesium

Help maintain normal muscle, heart and nerve function; supports a healthy immune system

Reference Range 0.7 – 1.0 mmol/L

Uric Acid

Used to diagnose and treat gout

Gout – Precipitation of uric acid in tissues and joints causing pain

Reference Range 0.21 – 0.44 mmol/L

Amylase-Clinical Significance

Used in the diagnosis and monitoring of acute pancreatitis

Hyperamylasemia also found in renal failure, lung or ovary tumors and pulmonary inflammation’

Reference Range

◦ Serum 28 - 100 U/L

◦ Urine 0 - 460 U/L

Acid Phosphatase

An enzyme which is increased in Prostatic Cancer

Serum is acidified after separation for Acid Phosphate test

Kidney/Renal Function Profiles

Kidneys – eliminate waste products for homeostasis; production of hormones Profile (test) for kidney disease include:

◦ Creatinine/clearance, BUN, eGFR, Uric Acid and 24-hour urine

Creatinine

Waste product of creatine phosphate

◦ Increased in impaired kidney functions

◦ Very useful in assessing kidney disease

◦ Reference Range 62 – 125 μmol/L

BUN/Urea – Blood Urea Nitrogen

◦ Measurement of urea in the blood

◦ Urea – Conversion of surplus amino acids

◦ Influenced by diet, hormones and kidney functions

◦ Reference Range 2.9 – 6.4 mmol/L

eGFR - Estimated Glomerular Filtration Rate

• – To assess kidney function

◦ Performed by ordering a creatinine test and calculating the eGFR using the age, gender, and race of the patient

◦ Normal values are 90 – 120 mL/min

◦ Below 60 mL/min suggest that some kidney damage has occurred