17) Analytical variables Flashcards
anything that may affect test results, which would result in an incorrect result
analytical variable
tracks errors and strives to find solutions to sources of error
quality assurance (QA) department
4 types of preanalytical variables
physiologic
specimen collection
handling of specimens
interferences
analytes affected by diurnal variation
BUN, aldosterone, bilirubin, catecholamines, cortisol, testosterone, luteinizing and follicle stimulating hormone, iron, potassium, thyroxine-stimulating hormone, triglycerides, uric acid and therapeutic drugs
analytes affected by exercise level
bilirubin, creatine kinase, aspartate aminotransferase, high-density lipoprotein cholesterol, lactate dehydrogenase, myoglobin, and uric acid
high protein diet effects
increase uric acid, urea, and ammonia levels
caffeine effects
decreases pH, increases ionized calcium and catecholamine levels
smoking effects
increases glucose, triglycerides, cholesterol, LDL cholesterol, ammonia
alcohol short term effects
decreases glucose, increase in plasma lactate, increases uric acid and triglycerides
alcohol moderate intake effects
increases HDL
alcohol long term effects
increases gamma glutamyltransferase, aspartate aminotransferase and alanine aminotransferase
prolonged fasting effects
Decreases prealbumin, glucose, albumin, LD, HDL cholesterol, ketones, and insulin
dehydration effects
Results in hemoconcentration, which falsely elevates iron, calcium, sodium, and enzymes
NIH recommendation for patient positioning
patients sit for 5 minutes before collecting a specimen for lipid testing
effects of standing vs supine
decrease in aldosterone, ADH, catecholamines, renin, albumin, ALP, ALT, bilirubin, calcium, cholesterol, total protein, and triglycerides
examples of physiologic variables
- age, ethnicity, gender
- diurnal variation
- exercise
- lifestyle/diet
- nonfasting/prolonged fasting
- dehydration
- pt position
examples of specimen collection variables
- requisition errors
- tourniquet time
- cleaning agent
- IV fluids/contamination
- drug interference
- capillary vs venous, serum vs plasma
- additives
- tube order
- short draw
- mixing
- labelling
- specific collections for micro
effects of long tourniquet time
increase in the ratio of cellular elements to plasma (hemoconcentration) and by causing hemolysis
analytes affected by long tourniquet time
those measuring large molecules, such as plasma proteins and lipids, or analytes affected by hemolysis, including potassium, lactic acid, and enzymes
betadine effects
falsely increase the phosphorus, uric acid and K+
Isopropyl (70%) alcohol cannot be used when…
collecting medical or legal ethanol specimens
IV draw procedure
not below IV
IV has been turned off for 2 – 5 min
draw a waste tube (10 mL, thrown away, usually a red top)
examples of IV contamination effects
Na and Cl may be increased, everything else diluted out.
Extremely high glucose, potassium, etc
analytes that require a conversion factor when EDTA plasma is used
cholesterol, triglycerides and HDL should be multiplied by 1.03 to be equivalent to a serum result
Capillary glucose values are —- higher than in venous specimens
1.4%
EDTA used for…
CBC’s, platelet count, ammonia, reticulosytes, sedimentation rates, A1c
Calcium could be less than test
Potassium could be greater than test
EDTA contamination
purple top/pink top
EDTA
lithium heparin used for…
BMP, CMP, troponin, CKMB, ionized calcium (on ice)
lithium heparin not used for…
lithium
duh
mint green with gel, dark green without gel
lithium heparin
heparin general function
acts to activate antithrombin to prevent the formation of fibrin, which stops clotting
sodium heparin used for…
cytogenetics
dark green
sodium heparin
Never in chemistry
sodium heparin
balanced heparin used for…
Blood gases and whole blood sodium and potassium performed on a blood gas analyzer
syringe tube additive
balanced heparin
sodium oxalate fluoride used for…
glucose (gold standard glycolysis inhibitor), lactic acid and ethanol
sodium oxalate fluoride not used for…
electrolytes, because it alters the blood cell membrane permeability
gray top
sodium oxalate fluoride
Inhibits coagulation by forming insoluble complexes with calcium ions
sodium oxalate fluoride
SST/nonSST used for…
BMP’s, CMP’s and most chemistry tests
SST/nonSST not used for…
therapeutic drug levels (in those with gel)
Contains a clot activator to promote clotting; gel separates RBCs from serum
SST
gold top with gel, red top without gel
SST/nonSST
sodium citrate used for…
PT, PTT, INR coagulation tests
light blue top
sodium citrate
Acid citrate dextrose. Can be used for fungal cultures and bone marrows.
blood culture tubes
yellow tops
blood culture tubes
royal blue top
Metal free tube for trace metal testing. Often made of glass as plastics can contain metal ions.
why might we use a glass tube instead of plastic?
Some analytes adhere to glass (vancomycin); others may be absorbed by the plastic tube if allowed to sit
order of tube draw
- blood cultures
- citrate or coagulation tubes
- serum (SST) tubes
- heparin tubes
- EDTA tubes
- fluoride tubes
….are collected in special tubes prepared by coag dept
pediatric APTTs and PTs
———- tubes get vigorously shaken.
tuberculosis
examples of specimen handling variables
- light
- temperature
- specimen processing
- prompt delivery
examples of interfering substances
- hemolysis
- icterus
- lipemia
- fibrin
analytes that must be protected from light
bilirubin, vitamin B12, folate, vitamin A and carotene
Once centrifuged, plasma or serum should be separated from cells within ——–. (Unless SST or PST)
2 hours
subtract bilirubin/lipemia interference by measuring with two wavelengths to eliminate the increase/decrease in absorbance
bichromatic analysis
lipemia can be reduced by ——— of the sample
ultracentrifugation
how to handle fibrin in serum and plasma
Serum: Allow blood to clot, no fibrin
Plasma: No need to wait to clot, contains fibrin
2 types of analytical variables
instrument
technologist
examples of instrument variables
- imprecision
- assay
- power source
- maintenance
- calibration
- QC
examples of postanalytical variables
- delivery of test results
- calling critical results
- LIS issues
- printer malfunction
- fax machine malfunction
- file results in wrong chart
example of critical result call documentation
Results called to Jane Smith, RN by Mindy D Lampe at 2:30 PM on 11/12/2018 and read back verified.
