Knowing normal laboratory values helps nurses spot problems early, escalate concerns and answer exam questions confidently. This cheat sheet covers the most commonly tested and used values, in both SI units (used in the UK, Nigeria, most of Africa, Europe and Australia) and US conventional units (used in the United States and on the NCLEX).
Important: reference ranges vary slightly between laboratories, ages, sexes and pregnancy. Always use your own laboratory’s ranges in practice. These values are typical adult ranges for learning.
Full blood count (FBC / CBC)
| Test |
SI units |
US units |
Notes |
| Haemoglobin (male) |
130 to 180 g/L |
13 to 18 g/dL |
Low = anaemia |
| Haemoglobin (female) |
120 to 160 g/L |
12 to 16 g/dL |
Lower in pregnancy (anaemia if below about 110 g/L) |
| White cell count (WBC) |
4.0 to 11.0 × 10⁹/L |
4,000 to 11,000/mm³ |
High = infection, inflammation; low = infection risk |
| Neutrophils |
2.0 to 7.5 × 10⁹/L |
2,000 to 7,500/mm³ |
Below 0.5 = severe neutropenia |
| Platelets |
150 to 400 × 10⁹/L |
150,000 to 400,000/mm³ |
Low = bleeding risk |
| Haematocrit (male) |
0.40 to 0.52 |
40 to 52% |
High in dehydration |
| Haematocrit (female) |
0.36 to 0.48 |
36 to 48% |
|
| MCV |
80 to 100 fL |
80 to 100 fL |
Low = iron deficiency; high = B12/folate deficiency |
Urea and electrolytes (U&E / BMP)
| Test |
SI units |
US units |
Notes |
| Sodium (Na⁺) |
135 to 145 mmol/L |
135 to 145 mEq/L |
Low = confusion, seizures; high = dehydration |
| Potassium (K⁺) |
3.5 to 5.0 mmol/L |
3.5 to 5.0 mEq/L |
Both high and low can cause dangerous arrhythmias |
| Chloride (Cl⁻) |
98 to 106 mmol/L |
98 to 106 mEq/L |
|
| Bicarbonate (HCO₃⁻) |
22 to 29 mmol/L |
22 to 29 mEq/L |
Low in metabolic acidosis |
| Urea |
2.5 to 7.8 mmol/L |
BUN 7 to 20 mg/dL |
High in kidney injury, dehydration, GI bleeding |
| Creatinine |
60 to 110 µmol/L (varies by sex and muscle mass) |
0.6 to 1.2 mg/dL |
Rising = kidney injury |
| eGFR |
Above 90 mL/min/1.73 m² |
Above 90 |
Below 60 for 3 months = chronic kidney disease |
Other electrolytes and minerals
| Test |
SI units |
US units |
| Calcium (total, adjusted) |
2.2 to 2.6 mmol/L |
8.5 to 10.5 mg/dL |
| Magnesium |
0.7 to 1.0 mmol/L |
1.7 to 2.4 mg/dL |
| Phosphate |
0.8 to 1.5 mmol/L |
2.5 to 4.5 mg/dL |
Blood glucose
| Test |
SI units |
US units |
| Fasting plasma glucose (normal) |
3.9 to 5.5 mmol/L |
70 to 99 mg/dL |
| Diabetes (fasting) |
7.0 mmol/L or higher |
126 mg/dL or higher |
| Random glucose suggesting diabetes (with symptoms) |
11.1 mmol/L or higher |
200 mg/dL or higher |
| Hypoglycaemia |
Below 4.0 mmol/L (treat) |
Below 70 mg/dL |
| HbA1c (normal) |
Below 42 mmol/mol |
Below 6.0% |
| HbA1c (diabetes) |
48 mmol/mol or higher |
6.5% or higher |
Tip: to convert glucose from mmol/L to mg/dL, multiply by 18.
Liver function tests (LFTs)
| Test |
Typical range |
Notes |
| Bilirubin (total) |
3 to 21 µmol/L (0.2 to 1.2 mg/dL) |
High = jaundice |
| ALT |
Below about 40 U/L |
Liver cell damage |
| AST |
Below about 40 U/L |
Liver, heart, muscle |
| ALP |
30 to 130 U/L |
Bile duct obstruction, bone disease |
| Albumin |
35 to 50 g/L (3.5 to 5.0 g/dL) |
Low in malnutrition, liver disease, kidney disease |
Clotting
| Test |
Typical range |
Notes |
| PT (prothrombin time) |
10 to 14 seconds |
Prolonged with warfarin, liver disease |
| INR |
0.8 to 1.2 (not on anticoagulation) |
Target usually 2.0 to 3.0 on warfarin for most indications |
| APTT |
25 to 35 seconds |
Monitors unfractionated heparin |
| Fibrinogen |
1.5 to 4.0 g/L |
Low in DIC and massive bleeding |
Arterial blood gases (ABG)
| Value |
Normal range |
| pH |
7.35 to 7.45 |
| PaCO₂ |
4.7 to 6.0 kPa (35 to 45 mmHg) |
| PaO₂ (on air) |
10 to 13 kPa (75 to 100 mmHg) |
| HCO₃⁻ |
22 to 26 mmol/L |
| Base excess |
−2 to +2 |
| Lactate |
Below 2 mmol/L |
A lactate of 2 mmol/L or more in suspected sepsis needs urgent escalation; 4 or more is a sign of severe illness.
Cardiac and inflammatory markers
- Troponin: laboratory-specific; a rise above the upper reference limit, especially with a rising pattern, suggests heart muscle damage.
- CRP: below 5 mg/L (raised in infection and inflammation).
- BNP / NT-proBNP: raised in heart failure; cut-offs vary by age and lab.
Other useful values
- Total cholesterol: below 5.0 mmol/L (below 200 mg/dL) is often targeted.
- TSH: about 0.4 to 4.0 mU/L.
- Urine output: at least 0.5 mL/kg/hour in adults.
- Urine specific gravity: 1.005 to 1.030.
- Digoxin therapeutic level: roughly 0.5 to 2.0 ng/mL (lower targets often used in heart failure).
- Lithium therapeutic level: typically 0.4 to 1.0 mmol/L.
Critical values: when to escalate immediately
- Potassium below 2.5 or above 6.0 mmol/L
- Sodium below 120 or above 160 mmol/L
- Glucose below 3.0 mmol/L (54 mg/dL) or very high with ketones
- Haemoglobin below 70 g/L, or a rapid fall
- Platelets below 20 × 10⁹/L
- pH below 7.2 or above 7.6
- Lactate 4 mmol/L or more
- INR far above target with bleeding
Always assess the patient as well as the number. A “normal” result in an unwell patient doesn’t mean everything is fine, and an abnormal result may be expected in some conditions.
Memory tips for exams
- Potassium 3.5 to 5: “K is a 3.5-to-5-star rating.”
- Sodium 135 to 145: “Salt is 135 to 145.”
- pH 7.35 to 7.45, CO₂ 35 to 45, HCO₃ 22 to 26 (in mmHg and mEq).
- Platelets 150 to 400.
- WBC 4 to 11.
References
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