FACTORS THAT MAY INFLUENCE CLINICAL LABORATORY RESULTS Dr KB Sedumedi DEPT OF CHEMICAL PATHOLOGY

OUTLINE  Clinical Laboratory Results - Role in Clinical Medicine  Task: Examples of patients’ results  Factors that may influence Laboratory Results - Pre-Analytical Factors - Analytical Factors - Post-Analytical Factors  Handling Of Laboratory Results - Interpretation of Laboratory Results - Critical evaluation of Laboratory Results  Conclusion & Recommendation

CLINICAL LABORATORY RESULTS (PATHOLOGY RESULTS) Role in Clinical Medicine  Pathology = the study of disease  Pathology laboratory results – crucial in confirming or r/o presence of disease - Used for: screening, diagnosis, monitoring & prognosis - require knowledge and understanding of biochemistry, anatomy, physiology & pathophysiological mechanism of diseases  Applicable across all Medical Specialties

Analyte (Serum) Patient APatient BPatient CPatient D Na + N N N ↑ K+K+ ↑↑ ↑ ↑ ↓ Cl - N N N ↑ Urea N N N ↓ LDH N ↑ - - ALP ↓ TP N - ↑ ↓ Calcium ↓↓ N ↑ - Mg ↓ N - - PO4 N ↑ - - Please indicate possible pre-analytical factor that might be responsible for each of the following pattern of results (N=normal, ↑ =high, ↓=low, - = not done)

FACTORS THAT MAY INFLUENCE LABORATORY RESULTS  Classified into:  Pre-analytical factors  Analytical factors  Post-analytical factors Process/ sequence of events in laboratory results production Patient preparation -> sample collection -> transportation -> receipt and registration in the lab -> sample preparation and analysis -> results transmission/ manual entry into a computer -> verification & authorisation -> printing

Pre-Analytical Factors  From patient preparation -> sample collection -> transportation -> receipt & registration in the laboratory  Physiological & non physiological factors 1. Patient Preparation a) Diet e.g. Lipid profile (egg yolk, dairy products, poultry (skin), organ meat, butter) glucose (high carbohydrate), uric acid (high protein) b) Drugs - may influence normal physiological processes e.g. Phenytoin(ɤGT) - may cause methodological interferences e.g. due to structural similarities or non specificity of the analytical method. e.g. salicylates & cimetidine (s-creatinine & creatinine clearance)

2. Sample collection a) Posture - Based on Starlings law of capillary exchange: Haemodynamic adaptation to postural change (e.g. lying to sitting and vice versa). - These postural changes will affect proteins & protein bound analytes e.g. Ca²˖, Fe²˖, Cholesterol, Triglycerides, etc. b) Prolonged application of tourniquet - ↑ Protein & protein bound analytes c) IV solutions - e.g. NaCl drip: ↑Na & Cl (other analytes ±↓) d) Hemolysis - narrow bore needle, tight tourniquet, sample clotting during collection  ↑ K, Mg, PO 3, AST, LDH

e) Sample tubes - e.g. K-EDTA will influence the following analytes: K(↑), Ca(↓), Mg(↓), Zn(↓), ALP(↓) f) Sequence of sample collection (multiple tubes) - tubes without preservatives 1 st g) Sample volume & mixing where necessary h) Type of sample - e.g. arterial vs venous blood: PCO 2, PO 2 i) Mislabeling of sample tubes j) Exercise - e.g. ↑ CK, AST, LDH etc. k) Sex - e.g. ↑ PSA i) Timing for sample collection Diurnal variation e.g. Cortisol

NB: Age and gender - e.g. ALP, creatinine, testosterone, oestradiol, etc. 3. Sample transportation a) Improper preservation e.g ice or not e.g. ACTH, ammonia, lactate, etc. b) Delayed transportation to the lab e.g. K, AST, ALT etc. 4. Sample receipt and registration a) Transcription or sample labelling error

Analytical Factors  From sample preparation -> analysis -> results production 1.Incomplete/ improper sample preparation 2.Poor instrument/ method performance Ensured by: - proper instrument/ method selection & evaluation (accurate/ precise/ sensitive & specific) - performance monitoring through rigorous quality assurance procedures (calibration & QC measures) Post-Analytical Factors  From results transmission/ manual entry into computer-> verification & authorization -> printing 1. Transcription/ transmission error of results Ensured by: - evaluation of the performance of the LIS - verification of results prior authorization

Handling of Laboratory Results  Interpretation Of Laboratory Results - Based on RR or RI values defined for a specific analyte -> ‘normal’/ within or ‘abnormal’/ outside? -> significantly different from ‘normal’/ previous results (if available)? -> consistent with the clinical findings? Reference Ranges (RR)/ Reference Interval (RI) - Definition: prediction interval/ range between which 95% (mean ± two SD) of values of a reference population will fall and 5% will be outside (2.5% on each side of this interval, i.e. below & above) -> determined statistically using values obtained from a healthy population - Limitations: 1) may differ across populations or subsets of populations 2) may differ across individuals within same population NB -> abnormal results not always = presence of disease -> normal results not always = absence of disease -> the greater the variation from the RI/ RR, the greater the probability of disease presence

NORMAL DISTRIBUTION OR GAUSSIAN CURVE Reference Ranges 12

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 Critical evaluation of laboratory results Requires the following: -> thorough review of clinical findings (hx & exam) (require sufficient knowledge & understanding of normal physiology and biochemical processes as well as the pathophysiological mechanisms of various clinical conditions) -> awareness of the limitations of the laboratory test RR/ RI -> consideration of possibility of pre-analytical, analytical & or post-analytical factors which might have affected the results

Conclusion and Recommendation  Quality of laboratory results relies on the quality of the sample as well as that of the analytical instrument/ method  crucial to ensure good quality sample & quality analytical process at all times: - proper patient prep & timing of sample collection, - correct; - sample collection technique & sequence, - sample tube, -sample volume & tube labelling - proper sample handling & transportation NB: The lab to provide information & support - quality analytical method & QC measures  Awareness of the limitations of the RR/ RI is crucial  always interpret results in conjunction with clinical findings + other results  if in doubt, do not treat, rather consult the lab or repeat the test to verify or determine the trend of results (NB: local EGK rules)