60 tests in 60 seconds
Graham Jones
Chemical Pathologist
St Vincent’s Hospital, Sydney
“10 words in 10 seconds”
• Sir Muir Grey
• A strategy we use to recall common pieces of
information
• Kernels: small chunks of useable knowledge
• Aphorisms
Aphorisms
• An aphorism is an original thought in a concise and
memorable form
• First used in the Aphorisms of Hippocrates. The oftcited first sentence of this work (see Ars longa, vita
brevis) is:
– Life is short, art long, opportunity fleeting,
experience deceptive, judgment difficult.
• In modern usage an aphorism is generally
understood to be a concise statement containing a
subjective truth or observation cleverly and pithily
written.
Medical Aphorisms
• Time is generally the best doctor.
– Ovid
• If you don't put your finger in it, you'll put your
foot in it
– Gastroenterologist
• Collected medical sayings from Hippocrates to
Osler
Aphorisms
• It is easy to get a thousand prescriptions, but
hard to get one single remedy
• In a dangerous illness, call in three doctors.
– Chinese sayings
Serum Sodium
Test
Result
Sodium
155 H
Reference
Units
(135 - 145) mmol/L
• Hypernatraemia is dehydration until proven
otherwise
Hypernatraemia (mmol/L)
• Too much salt
Rare
– Iatrogenic
– Sea water drowning
– Mineralocorticoid excess + inadequate intake
or
• Not enough water
– Too young
– Too old
– Too Sick
– Prevented
– Thirst centre lesion
Common
• Hypernatraemia is
dehydration until
proven otherwise
Celcus (25BC – 55 AD)
• The art of medicine has almost no constant
rule.
• There are three words in medicine you must
never use: always, never and must
– Matthew Meerkin (chemical Pathologist ~1995)
Serum Sodium
Test
Sodium
Result
125 L
Reference Units
(135 - 145) mmol/L
• Hyponatraemia has many causes.
• For diagnosis you need the following:
– Medications
– State of hydration
– Urine sample (sodium and osmolality)
www.sydpath.com.au
www.sydpath.com.au
Drugs and Hyponatraemia
• www.sydpath.com.au
Serum Sodium
Test
Sodium
Result
125 L
Reference Units
(135 - 145) mmol/L
• There is no aphorism for hyponatraemia
Serum Potassium
Male age 60
Test
Potassium
Creatinine
eGFR
Result
5.7 H
75
95
Reference Units
(3.5 - 5.0) mmol/L
(50 - 110) umol/L
mL/min/1.73m2
There are many causes of false elevation of
potassium
Pseudo-Hyperkalaemia
•
•
•
•
•
•
•
•
Fist clenching
Sample in fridge (even shortly)
Delayed separation (> 6 hours)
High white cell count (leukaemia)
High platelet count (serum, gold top)
Traumatic collection (heelprick)
EDTA contamination (order of draw)
Drip arm
Serum Potassium
Male age 60
Test
Potassium
Creatinine
eGFR
Result
5.7 H
75
95
Reference Units
(3.5 - 5.0) mmol/L
(50 - 110) umol/L
mL/min/1.73m2
• High Potassium is less likely to be real with
normal renal function
• A normal kidney can excrete potassium easily –
but remember medications
Potassium
Male age 60
Test
Potassium
Creatinine
eGFR
Result
5.7 H
155 H
41 L
Reference Units
(3.5 - 5.0) mmol/L
(50 - 110) umol/L
>60
mL/min/1.73m2
• High Potassium is more likely to be real with
reduced renal function
Serum Potassium
Test
Potassium
Creatinine
eGFR
Result
2.3 L
75
95
Reference Units
(3.5 - 5.0) mmol/L
(50 - 110) umol/L
mL/min/1.73m2
• There are very few causes of falsely low serum
potassium
• Drip arm, wrong patient
Serum Bicarbonate
Test
Bicarbonate
Result
15 L
Reference Units
(22 - 32) mmol/L
• Low bicarbonate = metabolic acidosis
Test
Bicarbonate
Result
35 H
Reference Units
(22 - 32) mmol/L
• High bicarbonate = metabolic alkalosis
Serum Chloride
Test
Sodium
Potassium
Chloride
Bicarbonate
Anion Gap
Result
140
4.8
115 H
15 L
15
Reference
Units
(135 - 145)
(3.5 - 5.0)
(95 - 110)
(22 - 32)
(12 - 18)
mmol/L
mmol/L
mmol/L
mmol/L
mmol/L
• The only use of a serum chloride is to calculate
an anion gap
• The only use of an anion gap is to identify the
cause of a metabolic acidosis
Serum Chloride
Test
Sodium
Potassium
Chloride
Bicarbonate
Anion Gap
Result
140
4.8
115 H
15 L
15
Reference
Units
(135 - 145)
(3.5 - 5.0)
(95 - 110)
(22 - 32)
(12 - 18)
mmol/L
mmol/L
mmol/L
mmol/L
mmol/L
• Normal anion Gap metabolic acidosis
• Acid ingestion, diarrhoea, renal tubular acidosis,
compensation, endocrine causes …
Serum Chloride
Test
Sodium
Potassium
Chloride
Bicarbonate
Anion Gap
Result
140
4.8
100
15 L
30 H
Reference
Units
(135 - 145)
(3.5 - 5.0)
(95 - 110)
(22 - 32)
(12 - 18)
mmol/L
mmol/L
mmol/L
mmol/L
mmol/L
• High Anion gap metabolic acidosis
• Lactic acidosis, ketoacidosis, renal failure,
ingestions
Hippocratic Aphorisms
• Never work when hungry
(~400 BC)
Serum Urea
Female age 30
Test
Urea
Creatinine
Result
1.2 L
75
Reference Units
(3.5 - 8.0) mmol/L
(45 - 90) umol/L
• A low urea is usually a healthy person who is
not eating much protein
Graham’s Favourite Pathology Diagram
Concentration of
anything in blood
relates to:
• Rate of entry
• Rate of removal
Urea
Only low with
low protein
intake, no
muscle
breakdown and
normal kidneys
Removal
(GFR)
Protein Breakdown
- Dietary
- Muscle (ill)
Aphorisms - Chinese
• A dirty cook gives diarrhoea quicker than
rhubarb.
– Tung-Su Pai.
Creatinine
Male age 60
Test
Creatinine
eGFR
Urine ACR
Result
135 H
46 L
10 H
Reference Units
(50 - 110) umol/L
(≥ 60)
mL/min/1.73m2
(<2.5)
mg/mmol
• Creatinine alone is not sufficient for CKD staging
• Urine albumin creatinine ratio also needed
Aust
2012
KHA
www.kidney.org.au
Hippocrates Aphorisms
• I have never seen people over fifty recover from
renal disease
(~400 BC)
LFT
Test
ALP
GGT
Result
250 H
27
Reference
Units
(0 - 110)
U/L
(0 - 35) U/L
• Isolated Alkaline phosphatase rises – think of
bone
• Remember Physiological causes: neonates,
puberty, pregnancy, post menopause
LFT
Test
AST
ALT
GGT
Result
45 H
50 H
55 H
Reference
(0 - 30)
(0 - 30)
(0 - 50)
Units
U/L
U/L
U/L
• The commonest cause of mild elevations of
ASLT, ALT and GGT is fatty liver (N<25)
• The commonest causes of fatty liver are obesity,
diabetes and alcohol
LFT
Test
Result
AST
90 H
ALT
27
Creatine Kinase 1100 H
Reference
(0 - 30)
(0 - 30)
(0 - 150)
Units
U/L
U/L
U/L
• An increased AST without ALT can be due to
muscle damage (skeletal or cardiac)
• A CK can provide confirmation
Creatine Kinase (CK)
Test
Creatine Kinase
Result
870 H
Reference
(0 - 150)
Units
U/L
• Elevated CK is common with unaccustomed
exercise
• Timing matches muscle soreness (peak 2nd day,
last 3 – 4 days)
Hippocrates Aphorisms
• Sudden exertion is harmful to the sedentary
(~400 BC)
Tumour Markers
Test
CEA
Result
10 H
Reference
(0 - 3.0)
Units
ug/L
• Tumour markers are lousy for screening
(PSA is the best, and PSA is controversial)
• All tumour markers have benign causes of elevation
Hippocratic Aphorisms
• To do nothing is sometimes a good remedy
(~400 BC)
Cholesterol etc
Test
Result
Reference
Cholesterol
5.8
(<4.0)
mmol/L
Triglycerides
2.2 H
(<2.0)
mmol/L
HDL cholesterol
LDL cholesterol
Tot Chol: HDL
0.8 L
4.0 H
7.2
(≥1.0)
(<2.0)
mmol/L
mmol/L
• Lipids in untreated patients should be
interpreted by assessing absolute risk
Units
Cholesterol etc
Test
Targets
Result
Reference
Units
Cholesterol
5.8
(<4.0)
mmol/L
Triglycerides
2.2 H
(<2.0)
mmol/L
HDL cholesterol
LDL cholesterol
Tot Chol: HDL
0.8 L
4.0 H
7.2
(≥1.0)
(<2.0)
mmol/L
mmol/L
• Lipids in treated patients should be interpreted
against treatment targets
West Africa Proverb
• Poison should be tried out on a frog.
(the beginning of clinical trials?)
Cholesterol
Male age 18
Test
Result
Reference
Cholesterol
7.7 H
(<6.0)
mmol/L
Triglycerides
2.3
(<2.0)
mmol/L
1.2
(>1.0)
mmol/L
HDL cholesterol
Units
• Very high total cholesterol (>7.5 mmol/L) should
consider Familial Hypercholesterolaemia (FH)
www.athero.org.au/FH
www.heartfoundation.org.au
Aphorisms - Chinese
• The able doctor acts before sickness comes.
– Liu Kung Cho.
Triglycerides
Test
Cholesterol
Result
Reference
Units
11.2 H
(<4.0)
mmol/L
Triglycerides
35 H
(<2.0)
mmol/L
HDL cholesterol
LDL cholesterol
NA
NA
(≥1.0)
(<2.0)
mmol/L
mmol/L
• Triglycerides > 10 mmol/L are a risk for
pancreatitis (probably) not cardiovascular
disease
Urate
Male age 60 - Inflammed 1st MTP joint
Test
Urate
Result
0.39
Reference
(0.12 - 0.46)
Units
mmol/L
Target for urate lowering therapy is <0.36 mmol/L
• Serum urate has very little role for diagnosis of
gout
• Serum urate is vital for monitoring treatment of
gout
Hippocratic Aphorisms
• Science begets knowledge, opinion ignorance
• An important phase of medicine is the ability to
appraise the literature correctly
Folate
Test
RBC Folate
Result
1330
Reference
(>1000)
Units
nmol/L
• Folate measurements are rarely useful since the
introduction of folate fortification of bread
(2009).
Osler (1849 – 1929)
• In all things relating to disease, credulity
remains a permanent fact, uninfluenced by
civilization or education.
Spot Urine Creatinine
Spot Urine Sample (Patient A)
Test
U Creatinine
Result
2.5 L
Reference
Units
(8.0 - 16.0) mmol/L
Spot Urine Sample (Patient B)
Test
U Creatinine
Result
19.2 H
Reference
Units
(8.0 - 16.0) mmol/L
• Spot sample: creatinine concentration informs
about urine concentration and muscle mass
24 hour Urine Creatinine
24 hour Urine Sample
Test
U Creatinine
U Volume
Creat Excr
Result
12
2.2
26.4 H
Reference Units
(8.0 - 16.0) mmol/L
(5.0 - 16.0) mmol/day
• 24 hour urine sample: creatinine amount helps
assess adequacy of collection time
(high – more than 24 hours; low – less than 24)