Chemical Pathology Flashcards
Objectives
Organ and non-organ related diagnostic biochemical tests
The difference between screening and selective laboratory tests
Reasons/justifications for selective lab tests
Commonly used biological specimen in Chemical Pathology
What is Chemical Pathology Laboratory Test
Chemical Pathology is part of medicine and Pathology and the laboratory tests performed in this subdiscipline of pathology is to assist in
diagnosis of diseases
treatment of patients, and
management of patients
What are some egs of the Biological Specimens
blood sample – venous, capillary or arterial
urine sample – early morning sample (Pregnancy test), 24h urine (kidney test, GFR)
cerebrospinal fluid (CSF)
saliva
faeces – for occult blood tests etc
What is the purpose Biochemical Tests
i. Screening
non-diagnostic tests - done to establish reference range, for research or estimating prevalence or incidence rates of diseases. Not associated with clinical signs & symptoms of a disease.
ii. Diagnostic tests
also called selective tests or discretionary tests – battery of tests routinely done in any hospital; associated with clinical signs & symptoms of a disease.
Justifications/reasons for selective laboratory investigations
to confirm a provisional diagnosis e.g. measurement of plasma free T4 and TSH levels to confirm a clinical diagnosis of hyperthyroidism.
to refine a diagnosis e.g. determination of plasma ACTH level to differentiate b/w pituitary and adrenal causes of Cushing’s Syndrome (high level of cortisol). Or conjugated and unconjugated bilirubin to differentiate b/w pre-hepatic and post-hepatic jaundice.
to assess the severity of disease e.g. measurement of plasma urea or creatinine levels to assess the severity of renal disease or HbA1c to assess integrated blood glucose level for about 3 months
to monitor progress of disease e.g. measurement of plasma glucose and K+ levels to assess the treatment of patients with diabetic keto-acidosis or hyperglycaemia.
to detect complication e.g measurement of renal function tests (creatinine, GFR etc) to detect renal complication in diabetes patients.
To save cost – to avoid doing unnecessary laboratory investigations that will not help the patient or aid in diagnosis or treatment of the patient
Liver Function Tests (LFT)
LFT specifically assesses:
Catabolic functions of the liver
Anabolic (synthetic) functions of the liver
Excretory functions of the liver
Liver function tests cont’d
a. Synthetic function
Measure
plasma total protein – not liver specific because value includes Immunoglobulins that are not produced in the liver
Albumin – more specific for the liver
b. Enzyme activity or hepatocellular damage - measure plasma
alanine aminotransferase (ALT)
aspartate aminotransferase (AST)
alkaline phosphatase (ALP)
gamma-glutamyl transferase (GGT)
Liver function tests cont’d
c. Hepatic ion transport and excretion – measure plasma
Total bilirubin Conjugated bilirubin Unconjugated bilirubin
Urinary metabolites bilirubin
urobilinogen
Bilirubin is derived from red blood, myoglobin breakdown (will do bilirubin metabolism in Yr. 2)
RENAL FUNCTION TESTS
Functions of the kidney include:-
regulation of water, electrolyte and osmolality -
regulation of acid and base status
removal of waste products of metabolism
Removal of toxic substances
conversion of Vit. D to its active metabolite (1-25-Vit D)
NUMBER OF SOLUTE PARTICLES PER UNIT WEIGHT OF WATER USUALLY EXPRESSED AS MMOL/KG OF WATER
Renal function tests cont’d
Measurement of plasma/serum
Urea and/or Creatinine
Na+
K +
HCO3
PO4
Ca
GFR
Measurement of glomerular filtration rate (GFR) requires 24h urine collection while calculation of e-GFR requires gender, ethnicity, creatinine etc.
Thyroid function tests
These are tests done to assess thyroid gland diseases e.g. hyperthyroidism, hypothyroidism
The tests include:-
Plasma thyroxine (T4)
Plasma tri-iodothyronine (T3)
Free (unbound) T3 and T4
Plasma thyroid stimulating hormone (TSH)
Adrenal function tests
These are tests done to assess adrenal gland associated disease e.g. Cushing’s syndrome
Measure:
Early morning (9.00am) plasma cortisol
Late (2300H) plasma cortisol
Adrenocorticotrophic hormone (ACTH)
NB:
Cortisol concentration varies during the day – high in the morning and low in the evening. Diagnostic values in Cushing’s syndrome are best determined in the evening when the normal values are expected to be low.
Cardiac function tests
These are tests done to assess the heart function as in myocardial infarction:
Creatine kinase (CK)
Creatine kinase isoenzyme B (CKMB)
Heart specific lactate dehydrogenase isoenzyme (LD1 & LD2)
Troponin (I,T, C) more specific and time-dependent test
Myoglobulin currently more useful
Gonadal function tests
Tests used to assess the testis and ovaries in cases of infertility in a couple
For Males, measure
Plasma testosterone
Leutenising hormone (LH)
Follicle stimulating hormone (FSH)
Prolactin (PRL)
Gonadal function tests cont’d
For female, measure
Plasma progesterone
Plasma LH
Plasma FSH and
Plasma prolactin (PRL)
