Laboratory Tests
The central theme of the General Medicine course is as follows:
Systemic diseases cause alterations in normal physiology and function.
These alterations complicate the diagnosis and treatment of dental problems.
Clinicians need to identify and classify systemic disorders and appropriately
modify diagnosis and treatment planning in order to avoid systemic
complications. Diagnosis is based on: previous history, medication lists,
symptoms, clinical signs, clinical tests such as radiographs and laboratory data.
To fully appreciate laboratory data as a diagnostic tool, one must have an
understanding of:
Organ systems: cardiovascular, respiratory, renal, hepatic, etc.
Anatomy and physiology
Disease states and classification
Diagnosis and treatment including pharmacology
Example: Diabetes mellitus
Organ:
endocrine pancreas
Anatomy: endocrine gland (alpha cells: glucagon, beta cells: insulin),
secretes directly into the systemic circulation
Physiology: glucose is regulated within a relatively narrow range (in part) by the
effects of insulin which drives the uptake of glucose into cells and glucagon
which stimulates the production of glucose through the metabolism of glycogen
and release of the glucose into the blood
Disease:
diabetes (Type I or II) as a result of loss of pancreatic insulin
production or systemic cellular sensitivity leading to a build up of serum glucose.
There is an inability of cells to take up glucose and a resulting “cellular starvation”
leading to alternate metabolic pathways (ketoacidosis).
Treatment: diet and exercise management, oral hypoglycemics or insulin
Test: Measurement of serum glucose gives the clinician insight into the
presence or absence of disease, its severity, patient compliance and control.
As we progress through the course, a number of lab values will come up as
important markers of organ function, dysfunction or treatment. This list is not
meant to be exhaustive. It is intended to be a reference for the more commonly
used (and therefore important) ones.
Commonly ordered tests:
CBC (complete blood count) offers insight into the function of the haematopoeitic
system … the production of hemoglobin, red blood cells, white blood cells and
platelets.
Hemoglobin
male
female
male
female
135 - 170 g/L
115 - 160 g/L
Hematocrit
0.40 - 0.51
0.34 - 0.48
RBCs
4.50 - 6.00 x 1012/L
RBC indices are useful to the hematologist in diagnosing a patient’s
anemia, for example iron deficiency vs. pernicious anemia eg. MCV
(mean corpuscular volume), MCH (mean corpuscular hemoglobin),
MCHC (mean corpuscular hemoglobin concentration)
WBCs
4.0 - 10.0 x 109/L
WBC differential (neutrophils, lymphocytes, monocytes, eosinophils,
basophils)
Platelets
150 - 400 x 109/L
Disturbances to hemoglobin include anemia due to iron or other deficiency,
bleeding or marrow suppression such as chemotherapy.
WBC increases are due to steroid use, infection or leukemia, decrease due to
marrow suppression.
Platelet decreases are due to increased consumption (ITP or spenlomegaly), or
decreased production due to marrow suppression.
Coagulation Studies
INR (International normalized ratio
0.9 - 1.1
of PT or prothrombin time)
Therapeutic coumadin
2.0 - 3.0
Mechanical heart valves
2.5 - 3.5
PTT (partial thromboplastin time) 21 - 33 seconds
Therapeutic heparin
60 - 85 seconds
INR and PTT may be elevated due to loss of factor production in liver disease,
due to congenital deficiency such as hemophilia, or suppression with drugs such
as coumadin or heparin.
Renal function
Electrolytes … the common ions that are important in serum
Sodium
135 - 145 mmol/L
Potassium
3.5 - 5.5 mmol/L
Chloride
98 - 107 mmol/L
Bicarbonate
24 - 32 mmol/L
Electrolyte disturbances may be due to renal failure, alterations in hydration
(hypo or hyper), drug use (diuretics), alterations in pH (acidosis or alkalosis),
diabetic ketoacidosis, adrenal disease, etc.
Renal function tests (more specific)
BUN (blood urea nitrogen) 2.5-8.0 mmol/L
Creatinine
60-125 umol/L (from which is calculated
creatinine clearance)
Renal failure (and increasing BUN and creatinine) may be due to acute tubular
necrosis (due to hypotension), glomerulonephritis, diabetic nephropathy, urinary
tract infection, etc.
Liver function
Albumin
Bilirubin
AST (aspartate aminotransferase)
ALT (alanine aminotransferase)
35 - 50
3.4 - 17.1
10 - 42
10 - 40
g/L
umol/l
U/L
U/L
In liver failure (due to hepatitis or cirrhosis) serum albumin will be decreased due
to reduced production, serum bilirubin will be increased due to loss of liver
metabolic function, serum enzymes will be increased due to “leakage” of
contents of damaged cells.
Respiratory function
ABGs (arterial blood gases)
ph
PO2
PCO2
7.35 - 7.45
70 - 104 mm Hg
35 - 45
PFTs (pulmonary function tests) FEV1 (forced expiratory volume in one
second / percent of predicted based on total forced expiratory volume)
Normal
moderate disease
>70%
40 to 60 %
mild disease
severe disease
< 60%
<40%
Endocrine function
Calcium
2.12 - 2.62 mmol/L
Calcium levels will be reduced with dietary Vitamin D or calcium deficiency,
loss of parathyroid function (for example post thyroid surgery), etc.
TSH
Suppressed
Elevated
0.35 - 5.00
< 0.10
> 15.0
mIU/L
mIU/L
mIU/L
TSH is elevated in hypothyroidism due to primary thyroid deficiency disease.
TSH is depressed with excess exogenous thyroid hormone, Grave’s disease or a
secreting thyroid adenoma
Glucose (random)
3.6 - 11.0 mmol/L
Glucose (fasting)
3.9 - 6.1 mmol/L
Glycated hemoglobin (long term (3 month) measure of diabetic control)
Normal
4.0 - 6.0 %
Good
<7.0
%
Fair
7.0 to 8.9 %
Poor
>9.0
%
Increased serum glucose may be related to either undiagnosed diabetes, or
poorly controlled diabetes due to non-compliance or the “brittleness” of the
underlying disease.
Decrease serum glucose is typically due to insulin overdose or inadequate
dietary intake of calories in the face of insulin or oral hypoglycemic use
HIV studies
CD4 count
essentially normal immunity
Mild
Moderate
Severe
End Stage
>400
301 – 400
201 – 300
101 – 200
0 – 100
x 106/L
x 106/L
x 106/L
x 106/L
x 106/L