general lab 2

pre-analytical

variables that may affect results before the specimen is analyzed

analytical

variables that may affect results while the specimen is analyzed

post-analytical

variables that may affect results after the specimen is analyzed

pre-analytical phase - influencing factors

method independent effects on laboratory results of biological origin which can occur in vivo and in vitro

pre-analytical phase - modifiable

factors that lead to avoidable changes in analyte concentration and can be controlled by patient action or standardization, analyte concentration fluctuates over the course of the day

pre-analytical phase - modifiable factors

diet, physical activity

pre-analytical phase - unmodifiable factors

factors that lead to unavoidable changes in analyte concentration and cannot be controlled by patient action, addressed by partitioning reference intervals

pre-analytical phase - unmodifiable factors examples

age, race, gender, pregnancy, altitude

pre-analytical phase - interference factors

method dependent effects on laboratory results that occur after collection and can be endogenous or exogenous, nay be reduced or eliminated by selecting a more specific method

pre-analytical phase - interference factors endogenous

biological constituents of the same (natural) (ex: glucose, paraproteins, free hemoglobin, lipids, bilirubin)

pre-analytical phase - interference factors exogenous

either present ion the same or added to the sample during or after sampling (ex: drugs, herbal components, anticoagulants, tube additives)

pre endogenous interference factors, hemolysis causes

immunological mechanisms: autoantibodies (autoimmune hemolytic anemia), incomplete transfusion reaction (also biochemical, physical, and chemical causes all in vivo)

pre endogenous interference factors, lipemia removal of

lipids from the sample through ultracentrifugation at almost 2000000 (to separate lipid and aqueous layers)

pre specific consideration blood gas testing relevant factors

patient status: resting exercising, crying, anxious, ventilator setting: spontaneous breathing or assisted mechanical ventilation, mode of oxygen delivery, respiratory rate: hyperventilation, hypoventilation, body temp

pre specific considerations, blood gas testing ideal sample CHECK THIS

lithium heparin, anticoagulated with lyophilized lithium heparin

pre specific consideration, hemostasis testing collection

pre specific consideration, hemostasis testing, platelet function analysis (PFA)

pre specific considerations in hematology underfilled

falsely decreased cell count and hematocrit; overfilled: clots, platelet clumps

pre specific considerations hematology stability

each lab should verify stability of hematologic parameters on their instruments

pre specific considerations cold agglutinins

monoclonal or polyclonal antibodies specific for erythrocyte surface carbohydrate antigens and bind at 0-4C

pre specific considerations signs of interference

pre specific considerations cryoglobulins signs

pre specific considerations, EDTA-dependent antibodies

pre-analytical variables identification

pre-analytical variables patient preparation

recent intake of food, alcohol, and drugs, smoking, exercising, stress, sleep, posture during collection

pre analytical variables turnaround time

delayed or lost requisitions, specimens, and result reports

pre analytical variables laboratory logs

specimen collection and receiving

pre analytical variables transcription errors

illegible handwriting

pre analytical variables specimen collection posture

seated or supine

pre analytical variables specimen collection needle selection

sterile, sharp, appropriate size, small bore needle can cause hemolysis

pre analytical variables sample collection site selection

avoid IV lines, hematomas, scarring, mastectomy, IV fluid dilutes specimen giving falsely decreased results

pre analytical specimen collection cleaning

allow alcohol to completely dry, can cause hemolysis

pre analytical variables

stress (can increase cortisol, TSH and growth hormone), fist pumping (increase plasma potassium, phosphate and lactate), tourniquet (increase protein concentration, order of draw, time, fill line

pre analytical variables hemolysis

pre analytical variables body fluids

pre analytical variables when handling specimen for analysis

maintain specimen identification, preservation (of temp, either frozen or body temp), light, separation, transport

pre analytical variables separation, plasma or serum separate within

must be controlled carefully to ensure accurate measurements by analytical methods

pre analytical variables urine temp

1 hr at room temperatures, 4 hours refrigerated, chemical constituents stable 24 hrs at 4C

reference values

results of a certain type of quantity obtained from a single individual or group of individuals corresponding to a stated description

in reference values the value range for a test or analyte that

most of the random population using the same testing method included

normal values vs reference ranges ?

used in the past but the term has become obsolete. Lacks conformity with different connotations

reference values health associated

values associated with a non diseased state, distinctions help prevent the misunderstanding that reference values are associated only with health, diabetic patient, hospitliized diabetic patient, ambulatory diabetic patient

reference values subject-based

previous values from the same individual obtained when the individual was in a defined state of health

reference values population based

obtained from a group of systematically defined reference individuals. The type of values referred to when the term reference values is used without qualifying words

positive diagnosis in reference valaues

condition of patient resembles what is considered typical of a particular disease

diagnosis by exclusion in reference values

observed symptoms and signs do not fit the pattern characterized by a set of alternative diseases

establish of reference values

a patients lab result is not medically useful if appropriate data for comparison are lacking

reference individual in reference values

an individual selected as the basis for comparison with individuals under clinical investigation through the use of defined criteria

random sample in reference individual

random sample of individuals in the parent population that meet selection criteria

selection of reference individuals in reference values

must be a random sample from the parent population who fulfill the selection criteria: statement of source population, specification of criteria for health or disease of interest

essential components required for a set of reference values are

analytical method: should include information on equipment, reagents, calibrators, type of raw data, and calculation method, quality control, and reliability criteria

sample collection in reference values

pre-analytical standardization to reduce bias and variation, preparation of the individual, sample collection, handling of specimen before analysis

exclusion criteria in reference values

used in established health-associated reference values, diseases, risk factors (obesity, occupation, genetics, hypertension), medication, physiological state (pregnancy, stress)

after the analysis of reference specimens is performed, the reference values are subject to

partitioning of the reference values into appropriate groups, inspection of distribution of each group, identification and handling of outliers, determination of reference limits

partitioning of reference values

use of specific criteria in the sub classification of reference groups to reduce the biological variation in each group, age, sex, genetic factor, physiological factor, other factors (environmental, socioeconomic, chronobiological)

inspection of distribution

highly deviating values (outliers) that may represent erroneous values, bimodal or polymodal distributions indicating nonhomogeneous results (reevaluate reference individuals selection criteria, partitioning of values)

identification of outliers

erroneous values that deviate significantly from the proper reference values, values near the furthest point on the long tail of a skewed distribution may be misinterpreted as outliers, deviating values identified as possible outliers should not be discarded automatically

determination of reference limits - reference interval

a set of values usually defined by an upper and lower reference limit, representing a specified proportion of the values frequently the central 95%

determination of reference limits - reference limits

describe the reference distribution and provide information about the observed variation of values in the selected set of reference individuals, observed patients values are compared with the corresponding reference interval, which is bounded by a pair of reference limits

determination of reference limits - clinical decision limits

provide optimal separations among clinical categories, usually based on analysis of reference values from several groups and thus sued for differential diagnosis

nonparametric analysis

statistical approach to reference value analysis that requires no assumptions about the distributions, Guassian or non-Gaussian, preferred method to establish reference intervals, requires 120 reference values per partition

parametric analysis

statical approach to reference value analysis that requires the distribution of values to be Gaussian

abnormal results often indicated in patietn values

low (yellow), high (purple), critical (red)