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Quick References

Adult reference ranges in SI units, critical values, Westgard rules, stains, tube colours and specimen handling — the tables every MLS student keeps coming back to.

For exam revision only. Reference ranges and critical limits vary by laboratory, method, analyser, age, sex and population. Always use the intervals validated and issued by your own laboratory for patient care.

Adult Haematology Reference Ranges Adult Chemical Pathology Reference Ranges Critical (Panic) Values Westgard QC Rules Common Stains & What They Demonstrate Anticoagulants & Tube Colours Specimen Storage & Transport Basics

Adult Haematology Reference Ranges

Full blood count, red cell indices and basic coagulation screen.

Haemoglobin (Hb)

Reference range: M 130–170 · F 120–150
Units: g/L
Notes: = 13.0–17.0 / 12.0–15.0 g/dL

Packed cell volume (PCV)

Reference range: M 0.40–0.50 · F 0.36–0.46
Units: L/L
Notes: = 40–50% / 36–46%

Red cell count (RBC)

Reference range: M 4.5–5.5 · F 3.8–4.8
Units: × 10¹²/L

Mean cell volume (MCV)

Reference range: 83–101
Units: fL
Notes: < 80 microcytic · > 100 macrocytic

Mean cell haemoglobin (MCH)

Reference range: 27–32
Units: pg

MCHC

Reference range: 315–345
Units: g/L
Notes: = 31.5–34.5 g/dL; raised in spherocytosis

Red cell distribution width (RDW-CV)

Reference range: 11.6–14.0
Units: %
Notes: Raised in iron deficiency, mixed populations

White cell count (WBC)

Reference range: 4.0–10.0
Units: × 10⁹/L
Notes: Often physiologically lower in people of African descent

Neutrophils

Reference range: 2.0–7.0
Units: × 10⁹/L
Notes: Benign ethnic neutropenia: down to ~1.0–1.5 may be normal

Lymphocytes

Reference range: 1.0–3.0
Units: × 10⁹/L

Monocytes

Reference range: 0.2–1.0
Units: × 10⁹/L

Eosinophils

Reference range: 0.02–0.5
Units: × 10⁹/L
Notes: Raised in helminth infection and allergy

Basophils

Reference range: 0.02–0.1
Units: × 10⁹/L

Platelets

Reference range: 150–400
Units: × 10⁹/L

Reticulocytes

Reference range: 0.5–2.5 (50–100 × 10⁹/L)
Units: %
Notes: Supravital stain (new methylene blue)

ESR (Westergren)

Reference range: M 0–10 · F 0–20
Units: mm/1st hour
Notes: Rises with age and in pregnancy

Prothrombin time (PT)

Reference range: 11–16
Units: s
Notes: Reagent dependent — use local range

INR

Reference range: 0.8–1.2
Units: —
Notes: Warfarin target usually 2.0–3.0

APTT

Reference range: 26–40
Units: s
Notes: Reagent dependent — use local range

Fibrinogen (Clauss)

Reference range: 2.0–4.0
Units: g/L

Bleeding time (Ivy)

Reference range: 2–7
Units: min
Notes: Platelet/vascular function

D-dimer

Reference range: < 0.5
Units: mg/L FEU
Notes: Assay dependent; age-adjusted cut-offs exist

Test	Reference range	Units	Notes
Haemoglobin (Hb)	M 130–170 · F 120–150	g/L	= 13.0–17.0 / 12.0–15.0 g/dL
Packed cell volume (PCV)	M 0.40–0.50 · F 0.36–0.46	L/L	= 40–50% / 36–46%
Red cell count (RBC)	M 4.5–5.5 · F 3.8–4.8	× 10¹²/L	—
Mean cell volume (MCV)	83–101	fL	< 80 microcytic · > 100 macrocytic
Mean cell haemoglobin (MCH)	27–32	pg	—
MCHC	315–345	g/L	= 31.5–34.5 g/dL; raised in spherocytosis
Red cell distribution width (RDW-CV)	11.6–14.0	%	Raised in iron deficiency, mixed populations
White cell count (WBC)	4.0–10.0	× 10⁹/L	Often physiologically lower in people of African descent
Neutrophils	2.0–7.0	× 10⁹/L	Benign ethnic neutropenia: down to ~1.0–1.5 may be normal
Lymphocytes	1.0–3.0	× 10⁹/L	—
Monocytes	0.2–1.0	× 10⁹/L	—
Eosinophils	0.02–0.5	× 10⁹/L	Raised in helminth infection and allergy
Basophils	0.02–0.1	× 10⁹/L	—
Platelets	150–400	× 10⁹/L	—
Reticulocytes	0.5–2.5 (50–100 × 10⁹/L)	%	Supravital stain (new methylene blue)
ESR (Westergren)	M 0–10 · F 0–20	mm/1st hour	Rises with age and in pregnancy
Prothrombin time (PT)	11–16	s	Reagent dependent — use local range
INR	0.8–1.2	—	Warfarin target usually 2.0–3.0
APTT	26–40	s	Reagent dependent — use local range
Fibrinogen (Clauss)	2.0–4.0	g/L	—
Bleeding time (Ivy)	2–7	min	Platelet/vascular function
D-dimer	< 0.5	mg/L FEU	Assay dependent; age-adjusted cut-offs exist

Adult Chemical Pathology Reference Ranges

Common serum/plasma analytes in SI units.

Glucose (fasting)

Reference range: 3.9–6.0
Units: mmol/L
Notes: Diabetes ≥ 7.0 fasting; ≥ 11.1 random/2-h OGTT

HbA1c

Reference range: < 6.0 (< 42)
Units: % (mmol/mol)
Notes: Diabetes ≥ 6.5% (48); unreliable in HbSS/haemolysis

Sodium (Na⁺)

Reference range: 135–145
Units: mmol/L

Potassium (K⁺)

Reference range: 3.5–5.0
Units: mmol/L
Notes: Falsely raised by haemolysis or delayed separation

Chloride (Cl⁻)

Reference range: 95–105
Units: mmol/L

Bicarbonate (HCO₃⁻)

Reference range: 22–29
Units: mmol/L

Anion gap

Reference range: 10–20 (8–16 without K⁺)
Units: mmol/L
Notes: (Na⁺ + K⁺) − (Cl⁻ + HCO₃⁻)

Urea

Reference range: 2.5–7.5
Units: mmol/L

Creatinine

Reference range: M 60–110 · F 45–90
Units: µmol/L
Notes: Depends on muscle mass

Uric acid

Reference range: M 0.20–0.42 · F 0.14–0.36
Units: mmol/L

Total protein

Reference range: 60–80
Units: g/L
Notes: Biuret method

Albumin

Reference range: 35–50
Units: g/L
Notes: Bromocresol green

Total bilirubin

Reference range: 3–21
Units: µmol/L
Notes: Protect sample from light

Conjugated bilirubin

Reference range: < 5
Units: µmol/L

ALT

Reference range: < 40
Units: U/L
Notes: More liver-specific than AST

AST

Reference range: < 40
Units: U/L
Notes: Also heart, muscle, red cells

Alkaline phosphatase (ALP)

Reference range: 30–130
Units: U/L
Notes: Higher in children and pregnancy

Gamma-GT (GGT)

Reference range: M < 55 · F < 38
Units: U/L
Notes: Confirms hepatic source of raised ALP

Calcium (total)

Reference range: 2.15–2.60
Units: mmol/L
Notes: Corrected = Ca + 0.02 × (40 − albumin g/L)

Phosphate

Reference range: 0.8–1.5
Units: mmol/L

Magnesium

Reference range: 0.7–1.0
Units: mmol/L

Total cholesterol

Reference range: < 5.2 (desirable)
Units: mmol/L

HDL cholesterol

Reference range: M > 1.0 · F > 1.2
Units: mmol/L

LDL cholesterol

Reference range: < 3.4 (desirable)
Units: mmol/L
Notes: Friedewald: TC − HDL − TG/2.2

Triglycerides (fasting)

Reference range: < 1.7
Units: mmol/L

Amylase

Reference range: 30–110
Units: U/L
Notes: > 3 × ULN suggests acute pancreatitis

Creatine kinase (CK)

Reference range: M 40–320 · F 25–200
Units: U/L
Notes: Raised after exercise, IM injection

Iron

Reference range: 10–30
Units: µmol/L

Ferritin

Reference range: M 30–400 · F 15–150
Units: µg/L
Notes: Acute-phase reactant — rises with inflammation

TSH

Reference range: 0.4–4.0
Units: mU/L

Free T4

Reference range: 10–25
Units: pmol/L

C-reactive protein (CRP)

Reference range: < 5
Units: mg/L

Lactate

Reference range: 0.5–2.2
Units: mmol/L

Osmolality

Reference range: 275–295
Units: mOsm/kg

CSF glucose

Reference range: 2.5–4.4 (~60% of plasma)
Units: mmol/L
Notes: Send paired blood glucose

CSF protein

Reference range: 0.15–0.45
Units: g/L

Arterial pH

Reference range: 7.35–7.45
Units: —

pCO₂ (arterial)

Reference range: 4.7–6.0
Units: kPa
Notes: = 35–45 mmHg

pO₂ (arterial, room air)

Reference range: 10.6–13.3
Units: kPa
Notes: = 80–100 mmHg

Base excess

Reference range: −2 to +2
Units: mmol/L

Test	Reference range	Units	Notes
Glucose (fasting)	3.9–6.0	mmol/L	Diabetes ≥ 7.0 fasting; ≥ 11.1 random/2-h OGTT
HbA1c	< 6.0 (< 42)	% (mmol/mol)	Diabetes ≥ 6.5% (48); unreliable in HbSS/haemolysis
Sodium (Na⁺)	135–145	mmol/L	—
Potassium (K⁺)	3.5–5.0	mmol/L	Falsely raised by haemolysis or delayed separation
Chloride (Cl⁻)	95–105	mmol/L	—
Bicarbonate (HCO₃⁻)	22–29	mmol/L	—
Anion gap	10–20 (8–16 without K⁺)	mmol/L	(Na⁺ + K⁺) − (Cl⁻ + HCO₃⁻)
Urea	2.5–7.5	mmol/L	—
Creatinine	M 60–110 · F 45–90	µmol/L	Depends on muscle mass
Uric acid	M 0.20–0.42 · F 0.14–0.36	mmol/L	—
Total protein	60–80	g/L	Biuret method
Albumin	35–50	g/L	Bromocresol green
Total bilirubin	3–21	µmol/L	Protect sample from light
Conjugated bilirubin	< 5	µmol/L	—
ALT	< 40	U/L	More liver-specific than AST
AST	< 40	U/L	Also heart, muscle, red cells
Alkaline phosphatase (ALP)	30–130	U/L	Higher in children and pregnancy
Gamma-GT (GGT)	M < 55 · F < 38	U/L	Confirms hepatic source of raised ALP
Calcium (total)	2.15–2.60	mmol/L	Corrected = Ca + 0.02 × (40 − albumin g/L)
Phosphate	0.8–1.5	mmol/L	—
Magnesium	0.7–1.0	mmol/L	—
Total cholesterol	< 5.2 (desirable)	mmol/L	—
HDL cholesterol	M > 1.0 · F > 1.2	mmol/L	—
LDL cholesterol	< 3.4 (desirable)	mmol/L	Friedewald: TC − HDL − TG/2.2
Triglycerides (fasting)	< 1.7	mmol/L	—
Amylase	30–110	U/L	> 3 × ULN suggests acute pancreatitis
Creatine kinase (CK)	M 40–320 · F 25–200	U/L	Raised after exercise, IM injection
Iron	10–30	µmol/L	—
Ferritin	M 30–400 · F 15–150	µg/L	Acute-phase reactant — rises with inflammation
TSH	0.4–4.0	mU/L	—
Free T4	10–25	pmol/L	—
C-reactive protein (CRP)	< 5	mg/L	—
Lactate	0.5–2.2	mmol/L	—
Osmolality	275–295	mOsm/kg	—
CSF glucose	2.5–4.4 (~60% of plasma)	mmol/L	Send paired blood glucose
CSF protein	0.15–0.45	g/L	—
Arterial pH	7.35–7.45	—	—
pCO₂ (arterial)	4.7–6.0	kPa	= 35–45 mmHg
pO₂ (arterial, room air)	10.6–13.3	kPa	= 80–100 mmHg
Base excess	−2 to +2	mmol/L	—

Critical (Panic) Values

Results that must be phoned to the clinician immediately and documented. Typical adult limits — each lab sets its own list.

Haemoglobin

Critical low: < 70
Critical high: > 200
Units / notes: g/L (< 7 / > 20 g/dL)

PCV

Critical low: < 0.20
Critical high: > 0.60
Units / notes: L/L

White cell count

Critical low: < 2.0
Critical high: > 30
Units / notes: × 10⁹/L; also any new blasts on film

Neutrophils

Critical low: < 0.5
Critical high: —
Units / notes: × 10⁹/L (severe neutropenia, infection risk)

Platelets

Critical low: < 20
Critical high: > 1000
Units / notes: × 10⁹/L

INR

Critical low: —
Critical high: > 5.0
Units / notes: Bleeding risk on warfarin

APTT

Critical low: —
Critical high: > 100
Units / notes: s (or > 3 × upper limit)

Fibrinogen

Critical low: < 1.0
Critical high: —
Units / notes: g/L (suspect DIC)

Malaria parasites

Critical low: —
Critical high: > 10% parasitised RBCs
Units / notes: WHO severe malaria criterion — report heavy parasitaemia urgently

Glucose

Critical low: < 2.5
Critical high: > 25
Units / notes: mmol/L (neonates: low limit ≈ 2.0–2.6)

Sodium

Critical low: < 120
Critical high: > 160
Units / notes: mmol/L

Potassium

Critical low: < 2.5
Critical high: > 6.5
Units / notes: mmol/L (exclude haemolysis first)

Calcium (corrected)

Critical low: < 1.75
Critical high: > 3.50
Units / notes: mmol/L

Magnesium

Critical low: < 0.4
Critical high: —
Units / notes: mmol/L

Phosphate

Critical low: < 0.3
Critical high: —
Units / notes: mmol/L

Bicarbonate

Critical low: < 10
Critical high: > 40
Units / notes: mmol/L

Arterial pH

Critical low: < 7.20
Critical high: > 7.60

pCO₂

Critical low: < 2.7
Critical high: > 9.3
Units / notes: kPa (20 / 70 mmHg)

pO₂

Critical low: < 6.7
Critical high: —
Units / notes: kPa (50 mmHg)

Lactate

Critical low: —
Critical high: > 4.0
Units / notes: mmol/L

Neonatal bilirubin

Critical low: —
Critical high: > 300
Units / notes: µmol/L (use age-specific treatment charts)

Troponin

Critical low: —
Critical high: Above MI cut-off
Units / notes: First positive result

Blood culture

Critical low: —
Critical high: Any positive
Units / notes: Report Gram stain result immediately

CSF

Critical low: —
Critical high: Positive Gram stain / culture / CrAg
Units / notes: Bacterial or cryptococcal meningitis

Notifiable pathogens

Critical low: —
Critical high: Suspected/confirmed
Units / notes: e.g. Lassa, cholera, meningococcus, diphtheria — notify per NCDC guidance

Analyte	Critical low	Critical high	Units / notes
Haemoglobin	< 70	> 200	g/L (< 7 / > 20 g/dL)
PCV	< 0.20	> 0.60	L/L
White cell count	< 2.0	> 30	× 10⁹/L; also any new blasts on film
Neutrophils	< 0.5	—	× 10⁹/L (severe neutropenia, infection risk)
Platelets	< 20	> 1000	× 10⁹/L
INR	—	> 5.0	Bleeding risk on warfarin
APTT	—	> 100	s (or > 3 × upper limit)
Fibrinogen	< 1.0	—	g/L (suspect DIC)
Malaria parasites	—	> 10% parasitised RBCs	WHO severe malaria criterion — report heavy parasitaemia urgently
Glucose	< 2.5	> 25	mmol/L (neonates: low limit ≈ 2.0–2.6)
Sodium	< 120	> 160	mmol/L
Potassium	< 2.5	> 6.5	mmol/L (exclude haemolysis first)
Calcium (corrected)	< 1.75	> 3.50	mmol/L
Magnesium	< 0.4	—	mmol/L
Phosphate	< 0.3	—	mmol/L
Bicarbonate	< 10	> 40	mmol/L
Arterial pH	< 7.20	> 7.60	—
pCO₂	< 2.7	> 9.3	kPa (20 / 70 mmHg)
pO₂	< 6.7	—	kPa (50 mmHg)
Lactate	—	> 4.0	mmol/L
Neonatal bilirubin	—	> 300	µmol/L (use age-specific treatment charts)
Troponin	—	Above MI cut-off	First positive result
Blood culture	—	Any positive	Report Gram stain result immediately
CSF	—	Positive Gram stain / culture / CrAg	Bacterial or cryptococcal meningitis
Notifiable pathogens	—	Suspected/confirmed	e.g. Lassa, cholera, meningococcus, diphtheria — notify per NCDC guidance

Westgard QC Rules

Multirule interpretation of internal quality control on a Levey–Jennings chart (SD = standard deviation from the control mean).

1₂s

Plain-English meaning: One control result is beyond ±2 SD.
Error type: Warning only
Action: Inspect the other rules before accepting the run

1₃s

Plain-English meaning: One control result is beyond ±3 SD.
Error type: Random (or large systematic)
Action: Reject run; troubleshoot

2₂s

Plain-English meaning: Two consecutive results beyond the same ±2 SD limit (same level twice, or both levels in one run).
Error type: Systematic
Action: Reject; check calibration/reagents

R₄s

Plain-English meaning: One control above +2 SD and another below −2 SD in the same run (range > 4 SD).
Error type: Random
Action: Reject; check pipetting, sampling, bubbles

4₁s

Plain-English meaning: Four consecutive results beyond the same ±1 SD limit.
Error type: Systematic (shift)
Action: Reject; recalibrate, check reagent lot

10ₓ

Plain-English meaning: Ten consecutive results on the same side of the mean.
Error type: Systematic (shift/bias)
Action: Reject; investigate calibration, reagent, instrument drift

2 of 3₂s

Plain-English meaning: Two of three controls beyond the same ±2 SD limit.
Error type: Systematic
Action: Reject

7T (trend)

Plain-English meaning: Seven consecutive results steadily rising or falling.
Error type: Systematic (trend)
Action: Investigate deterioration of reagent, lamp, calibrator

Rule	Plain-English meaning	Error type	Action
1₂s	One control result is beyond ±2 SD.	Warning only	Inspect the other rules before accepting the run
1₃s	One control result is beyond ±3 SD.	Random (or large systematic)	Reject run; troubleshoot
2₂s	Two consecutive results beyond the same ±2 SD limit (same level twice, or both levels in one run).	Systematic	Reject; check calibration/reagents
R₄s	One control above +2 SD and another below −2 SD in the same run (range > 4 SD).	Random	Reject; check pipetting, sampling, bubbles
4₁s	Four consecutive results beyond the same ±1 SD limit.	Systematic (shift)	Reject; recalibrate, check reagent lot
10ₓ	Ten consecutive results on the same side of the mean.	Systematic (shift/bias)	Reject; investigate calibration, reagent, instrument drift
2 of 3₂s	Two of three controls beyond the same ±2 SD limit.	Systematic	Reject
7T (trend)	Seven consecutive results steadily rising or falling.	Systematic (trend)	Investigate deterioration of reagent, lamp, calibrator

Shift = sudden change in the mean (new reagent lot, recalibration). Trend = gradual drift (deteriorating reagent, ageing lamp).
Random error affects precision; systematic error affects accuracy (bias).
Never simply repeat the control until it passes — find and correct the cause, then re-run patient samples if needed.

Common Stains & What They Demonstrate

Routine and special stains across microbiology, haematology, histopathology and cytology.

Gram

Demonstrates: Bacterial cell wall type
Result: Gram-positive purple; Gram-negative pink/red
Discipline: Microbiology

Ziehl–Neelsen

Demonstrates: Acid-fast bacilli (Mycobacterium)
Result: Red rods on blue background
Discipline: Microbiology / Histology

Modified ZN (cold, 1% H₂SO₄)

Demonstrates: Nocardia, Cryptosporidium, Cyclospora
Result: Red/pink on blue
Discipline: Microbiology / Parasitology

Auramine–rhodamine

Demonstrates: Acid-fast bacilli (fluorescence)
Result: Yellow-green fluorescent bacilli
Discipline: Microbiology

Albert

Demonstrates: Volutin granules of C. diphtheriae
Result: Blue-black granules in green bacilli
Discipline: Microbiology

India ink / nigrosin

Demonstrates: Capsule (Cryptococcus neoformans)
Result: Clear halo around yeast on dark background
Discipline: Microbiology

Lactophenol cotton blue

Demonstrates: Fungal structures
Result: Hyphae and spores stained blue
Discipline: Mycology

Giemsa

Demonstrates: Malaria and blood parasites; cell morphology
Result: Parasite chromatin red, cytoplasm blue
Discipline: Haematology / Parasitology

Leishman

Demonstrates: Blood and marrow cell morphology
Result: Nuclei purple, cytoplasm variable
Discipline: Haematology

Field's stain

Demonstrates: Rapid malaria thick films
Result: As Giemsa, in under a minute
Discipline: Parasitology

New methylene blue

Demonstrates: Reticulocytes; Heinz bodies
Result: Blue reticulum / inclusions
Discipline: Haematology

Perls' Prussian blue

Demonstrates: Ferric iron (haemosiderin)
Result: Bright blue
Discipline: Haematology / Histology

Sudan black B / MPO

Demonstrates: Myeloid granules (AML vs ALL)
Result: Black/brown granules in myeloid cells
Discipline: Haematology

Haematoxylin & eosin (H&E)

Demonstrates: General tissue morphology
Result: Nuclei blue; cytoplasm pink
Discipline: Histopathology

PAS (± diastase)

Demonstrates: Glycogen, neutral mucins, fungi, basement membrane
Result: Magenta (glycogen removed by diastase)
Discipline: Histopathology

Alcian blue (pH 2.5 / 1.0)

Demonstrates: Acid mucins / sulphated mucins
Result: Blue
Discipline: Histopathology

Congo red

Demonstrates: Amyloid
Result: Red; apple-green birefringence in polarised light
Discipline: Histopathology

Masson's trichrome

Demonstrates: Collagen vs muscle
Result: Collagen blue/green; muscle red; nuclei black
Discipline: Histopathology

Van Gieson

Demonstrates: Collagen
Result: Collagen red; muscle yellow
Discipline: Histopathology

Verhoeff / orcein

Demonstrates: Elastic fibres
Result: Black (Verhoeff) / brown (orcein)
Discipline: Histopathology

Gordon & Sweet's

Demonstrates: Reticulin fibres
Result: Black
Discipline: Histopathology

Oil Red O / Sudan IV

Demonstrates: Neutral lipids (frozen sections)
Result: Red-orange
Discipline: Histopathology

Von Kossa

Demonstrates: Calcium salts (phosphate/carbonate)
Result: Black
Discipline: Histopathology

Masson–Fontana

Demonstrates: Melanin, argentaffin granules
Result: Black
Discipline: Histopathology

Grocott methenamine silver

Demonstrates: Fungi, Pneumocystis
Result: Black organisms on green
Discipline: Histopathology

Warthin–Starry

Demonstrates: Spirochaetes, H. pylori
Result: Black organisms on yellow
Discipline: Histopathology

Toluidine blue

Demonstrates: Mast cells, cartilage (metachromasia)
Result: Purple-red granules on blue
Discipline: Histopathology

Papanicolaou (Pap)

Demonstrates: Cervical and other cytology
Result: Keratin orange; mature cells pink; immature blue-green
Discipline: Cytology

Stain	Demonstrates	Result	Discipline
Gram	Bacterial cell wall type	Gram-positive purple; Gram-negative pink/red	Microbiology
Ziehl–Neelsen	Acid-fast bacilli (Mycobacterium)	Red rods on blue background	Microbiology / Histology
Modified ZN (cold, 1% H₂SO₄)	Nocardia, Cryptosporidium, Cyclospora	Red/pink on blue	Microbiology / Parasitology
Auramine–rhodamine	Acid-fast bacilli (fluorescence)	Yellow-green fluorescent bacilli	Microbiology
Albert	Volutin granules of C. diphtheriae	Blue-black granules in green bacilli	Microbiology
India ink / nigrosin	Capsule (Cryptococcus neoformans)	Clear halo around yeast on dark background	Microbiology
Lactophenol cotton blue	Fungal structures	Hyphae and spores stained blue	Mycology
Giemsa	Malaria and blood parasites; cell morphology	Parasite chromatin red, cytoplasm blue	Haematology / Parasitology
Leishman	Blood and marrow cell morphology	Nuclei purple, cytoplasm variable	Haematology
Field's stain	Rapid malaria thick films	As Giemsa, in under a minute	Parasitology
New methylene blue	Reticulocytes; Heinz bodies	Blue reticulum / inclusions	Haematology
Perls' Prussian blue	Ferric iron (haemosiderin)	Bright blue	Haematology / Histology
Sudan black B / MPO	Myeloid granules (AML vs ALL)	Black/brown granules in myeloid cells	Haematology
Haematoxylin & eosin (H&E)	General tissue morphology	Nuclei blue; cytoplasm pink	Histopathology
PAS (± diastase)	Glycogen, neutral mucins, fungi, basement membrane	Magenta (glycogen removed by diastase)	Histopathology
Alcian blue (pH 2.5 / 1.0)	Acid mucins / sulphated mucins	Blue	Histopathology
Congo red	Amyloid	Red; apple-green birefringence in polarised light	Histopathology
Masson's trichrome	Collagen vs muscle	Collagen blue/green; muscle red; nuclei black	Histopathology
Van Gieson	Collagen	Collagen red; muscle yellow	Histopathology
Verhoeff / orcein	Elastic fibres	Black (Verhoeff) / brown (orcein)	Histopathology
Gordon & Sweet's	Reticulin fibres	Black	Histopathology
Oil Red O / Sudan IV	Neutral lipids (frozen sections)	Red-orange	Histopathology
Von Kossa	Calcium salts (phosphate/carbonate)	Black	Histopathology
Masson–Fontana	Melanin, argentaffin granules	Black	Histopathology
Grocott methenamine silver	Fungi, Pneumocystis	Black organisms on green	Histopathology
Warthin–Starry	Spirochaetes, H. pylori	Black organisms on yellow	Histopathology
Toluidine blue	Mast cells, cartilage (metachromasia)	Purple-red granules on blue	Histopathology
Papanicolaou (Pap)	Cervical and other cytology	Keratin orange; mature cells pink; immature blue-green	Cytology

Anticoagulants & Tube Colours

Common evacuated-tube colour codes. Listed in the recommended order of draw (CLSI). Colours can vary by manufacturer — always check the label.

Blood culture bottles

Additive: Broth (aerobic/anaerobic)
How it works: Supports bacterial growth
Main uses: Blood culture — always drawn first

Light blue

Additive: 3.2% trisodium citrate (9:1)
How it works: Binds calcium (reversible)
Main uses: PT/INR, APTT, fibrinogen, D-dimer — fill to the line

Black

Additive: 3.8% trisodium citrate (4:1)
How it works: Binds calcium
Main uses: Westergren ESR

Red

Additive: None or clot activator (silica)
How it works: Allows clotting → serum
Main uses: Serology, chemistry, blood bank (some labs)

Gold / yellow (SST)

Additive: Clot activator + separator gel
How it works: Gel separates serum on centrifugation
Main uses: Chemistry, hormones, serology

Green

Additive: Lithium or sodium heparin
How it works: Activates antithrombin, inhibiting thrombin
Main uses: Plasma chemistry, ammonia, blood gases (syringe)

Lavender / purple

Additive: K₂EDTA (1.5 mg/mL)
How it works: Chelates calcium (irreversible)
Main uses: FBC, blood film, HbA1c, Hb electrophoresis, CD4, viral load

Pink

Additive: K₂EDTA
How it works: Chelates calcium
Main uses: Blood grouping, antibody screen, crossmatch

Grey

Additive: Sodium fluoride + potassium oxalate
How it works: Fluoride inhibits glycolysis (enolase); oxalate anticoagulates
Main uses: Glucose, lactate, blood alcohol

Royal blue

Additive: Trace-element-free (± EDTA/heparin)
How it works: Metal-free tube
Main uses: Trace elements, toxicology (lead, zinc)

Pale yellow

Additive: ACD (acid citrate dextrose)
How it works: Binds calcium; dextrose preserves cells
Main uses: HLA typing, paternity/DNA tests

Cap colour	Additive	How it works	Main uses
Blood culture bottles	Broth (aerobic/anaerobic)	Supports bacterial growth	Blood culture — always drawn first
Light blue	3.2% trisodium citrate (9:1)	Binds calcium (reversible)	PT/INR, APTT, fibrinogen, D-dimer — fill to the line
Black	3.8% trisodium citrate (4:1)	Binds calcium	Westergren ESR
Red	None or clot activator (silica)	Allows clotting → serum	Serology, chemistry, blood bank (some labs)
Gold / yellow (SST)	Clot activator + separator gel	Gel separates serum on centrifugation	Chemistry, hormones, serology
Green	Lithium or sodium heparin	Activates antithrombin, inhibiting thrombin	Plasma chemistry, ammonia, blood gases (syringe)
Lavender / purple	K₂EDTA (1.5 mg/mL)	Chelates calcium (irreversible)	FBC, blood film, HbA1c, Hb electrophoresis, CD4, viral load
Pink	K₂EDTA	Chelates calcium	Blood grouping, antibody screen, crossmatch
Grey	Sodium fluoride + potassium oxalate	Fluoride inhibits glycolysis (enolase); oxalate anticoagulates	Glucose, lactate, blood alcohol
Royal blue	Trace-element-free (± EDTA/heparin)	Metal-free tube	Trace elements, toxicology (lead, zinc)
Pale yellow	ACD (acid citrate dextrose)	Binds calcium; dextrose preserves cells	HLA typing, paternity/DNA tests

Order of draw prevents additive carry-over — e.g. EDTA contamination of a chemistry sample gives falsely high K⁺ and low Ca²⁺.
Gently invert additive tubes 5–10 times after collection; do not shake.

Specimen Storage & Transport Basics

General guidance — follow your laboratory's SOPs and the test manufacturer's stability data.

Full blood count

Container / preservative: EDTA (lavender)
Transport: Room temperature
Stability / storage: Analyse within 24 h; make blood films within 2–3 h

Coagulation (PT/APTT)

Container / preservative: 3.2% citrate, correctly filled
Transport: Room temperature — do not refrigerate
Stability / storage: PT within 24 h; APTT within 4 h; freeze plasma (−20 °C or colder) for delays

Glucose

Container / preservative: Fluoride oxalate (grey)
Transport: Room temperature
Stability / storage: Stable ~24 h; a plain tube must be separated within 30 min

Electrolytes / routine chemistry

Container / preservative: Serum (SST) or heparin plasma
Transport: Room temperature
Stability / storage: Separate within 2 h; never refrigerate unseparated blood (K⁺ leaks out of cells)

Arterial blood gas

Container / preservative: Heparinised syringe, no air bubbles, capped
Transport: Room temperature (plastic syringe)
Stability / storage: Analyse within 30 min

Ammonia

Container / preservative: EDTA or heparin, filled completely
Transport: On ice
Stability / storage: Separate and analyse within 30 min

Bilirubin

Container / preservative: Serum/plasma
Transport: Protect from light (foil/amber tube)
Stability / storage: Light degrades bilirubin — analyse promptly

Routine urine (urinalysis)

Container / preservative: Clean, dry container
Transport: Room temperature
Stability / storage: Examine within 2 h, or refrigerate at 4 °C up to 24 h

Urine culture

Container / preservative: Sterile container (MSU) or boric acid
Transport: Room temperature if within 2 h
Stability / storage: Otherwise 4 °C up to 24 h or boric acid

24-hour urine

Container / preservative: Large container ± preservative (e.g. HCl for catecholamines)
Transport: Keep cool during collection
Stability / storage: Discard first void, include last; record total volume

Blood culture

Container / preservative: Aerobic + anaerobic bottles (8–10 mL each, adult)
Transport: Room temperature — never refrigerate
Stability / storage: Load into incubator as soon as possible

CSF

Container / preservative: Sterile tubes (separate for micro, chemistry, cytology)
Transport: Room temperature or 37 °C, immediately
Stability / storage: Never refrigerate for bacteriology; process at once

Swabs (bacteriology)

Container / preservative: Amies or Stuart transport medium
Transport: Room temperature
Stability / storage: Process within 24 h; do not refrigerate gonococcal swabs

Sputum for AFB / GeneXpert

Container / preservative: Sterile, leak-proof, wide-mouthed container
Transport: Cool box if delayed
Stability / storage: Early-morning sample; refrigerate at 2–8 °C if not processed same day

Stool for parasites

Container / preservative: Clean container; 10% formalin or PVA if delayed
Transport: Room temperature
Stability / storage: Liquid stool within 30 min, formed within 1 h for trophozoites

Stool for culture

Container / preservative: Cary–Blair transport medium
Transport: 4 °C if delayed
Stability / storage: Process within 24 h

Histology tissue

Container / preservative: 10% neutral buffered formalin, 10–20 × tissue volume
Transport: Room temperature, leak-proof container
Stability / storage: Send fresh (no fixative) only for frozen section, culture or flow cytometry

Cervical / FNA smears

Container / preservative: 95% ethanol wet fixation or spray fixative (LBC vial)
Transport: Room temperature
Stability / storage: Fix immediately — air drying spoils Pap staining

Serum for serology

Container / preservative: Plain/SST tube, separated
Transport: 2–8 °C
Stability / storage: 2–8 °C up to ~5–7 days; −20 °C or colder long term; avoid repeated freeze–thaw

Dried blood spot (EID, HIV)

Container / preservative: Filter-paper card
Transport: Gas-impermeable bag with desiccant
Stability / storage: Air-dry ≥ 3–4 h flat, away from sunlight before packing

Crossmatch sample

Container / preservative: EDTA (pink/lavender), fully labelled at bedside
Transport: Room temperature or 2–8 °C
Stability / storage: Use within 72 h if transfused or pregnant in the last 3 months

Routine diagnostic specimens (shipping)

Container / preservative: Triple packaging, UN3373 (Category B)
Transport: Primary + secondary leak-proof + rigid outer
Stability / storage: Absorbent material between primary and secondary containers

High-risk specimens (e.g. Lassa)

Container / preservative: Triple packaging, UN2814 (Category A)
Transport: Trained shipper; cold chain
Stability / storage: Send only to designated NCDC reference laboratories

Specimen	Container / preservative	Transport	Stability / storage
Full blood count	EDTA (lavender)	Room temperature	Analyse within 24 h; make blood films within 2–3 h
Coagulation (PT/APTT)	3.2% citrate, correctly filled	Room temperature — do not refrigerate	PT within 24 h; APTT within 4 h; freeze plasma (−20 °C or colder) for delays
Glucose	Fluoride oxalate (grey)	Room temperature	Stable ~24 h; a plain tube must be separated within 30 min
Electrolytes / routine chemistry	Serum (SST) or heparin plasma	Room temperature	Separate within 2 h; never refrigerate unseparated blood (K⁺ leaks out of cells)
Arterial blood gas	Heparinised syringe, no air bubbles, capped	Room temperature (plastic syringe)	Analyse within 30 min
Ammonia	EDTA or heparin, filled completely	On ice	Separate and analyse within 30 min
Bilirubin	Serum/plasma	Protect from light (foil/amber tube)	Light degrades bilirubin — analyse promptly
Routine urine (urinalysis)	Clean, dry container	Room temperature	Examine within 2 h, or refrigerate at 4 °C up to 24 h
Urine culture	Sterile container (MSU) or boric acid	Room temperature if within 2 h	Otherwise 4 °C up to 24 h or boric acid
24-hour urine	Large container ± preservative (e.g. HCl for catecholamines)	Keep cool during collection	Discard first void, include last; record total volume
Blood culture	Aerobic + anaerobic bottles (8–10 mL each, adult)	Room temperature — never refrigerate	Load into incubator as soon as possible
CSF	Sterile tubes (separate for micro, chemistry, cytology)	Room temperature or 37 °C, immediately	Never refrigerate for bacteriology; process at once
Swabs (bacteriology)	Amies or Stuart transport medium	Room temperature	Process within 24 h; do not refrigerate gonococcal swabs
Sputum for AFB / GeneXpert	Sterile, leak-proof, wide-mouthed container	Cool box if delayed	Early-morning sample; refrigerate at 2–8 °C if not processed same day
Stool for parasites	Clean container; 10% formalin or PVA if delayed	Room temperature	Liquid stool within 30 min, formed within 1 h for trophozoites
Stool for culture	Cary–Blair transport medium	4 °C if delayed	Process within 24 h
Histology tissue	10% neutral buffered formalin, 10–20 × tissue volume	Room temperature, leak-proof container	Send fresh (no fixative) only for frozen section, culture or flow cytometry
Cervical / FNA smears	95% ethanol wet fixation or spray fixative (LBC vial)	Room temperature	Fix immediately — air drying spoils Pap staining
Serum for serology	Plain/SST tube, separated	2–8 °C	2–8 °C up to ~5–7 days; −20 °C or colder long term; avoid repeated freeze–thaw
Dried blood spot (EID, HIV)	Filter-paper card	Gas-impermeable bag with desiccant	Air-dry ≥ 3–4 h flat, away from sunlight before packing
Crossmatch sample	EDTA (pink/lavender), fully labelled at bedside	Room temperature or 2–8 °C	Use within 72 h if transfused or pregnant in the last 3 months
Routine diagnostic specimens (shipping)	Triple packaging, UN3373 (Category B)	Primary + secondary leak-proof + rigid outer	Absorbent material between primary and secondary containers
High-risk specimens (e.g. Lassa)	Triple packaging, UN2814 (Category A)	Trained shipper; cold chain	Send only to designated NCDC reference laboratories

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