Contents · 12 sections
- 1. General principles
- 2. Complete blood count (CBC)
- 3. Biochemistry — proteins and nitrogenous compounds
- 4. Liver function tests
- 5. Lipid profile
- 6. Carbohydrates and kidneys
- 7. Electrolytes and ABG / acid-base balance
- 8. Cardiac markers
- 9. Coagulation profile
- 10. Inflammation and immunology
- 11. Hormones — key
- 12. FAQ
In a nutshell. Reference intervals represent 95% of a healthy population. Critical ("panic") values require immediate action: K⁺ < 2.5 or > 6.5 mmol/L, Na⁺ < 120 or > 160, glucose < 2.2 or > 25, pH < 7.2 or > 7.6, Hb < 70 g/L, platelets < 20×10⁹/L, INR > 5, troponin above the 99th percentile in any concentration with symptoms of ACS. Always interpret in conjunction with clinical presentation, age, sex, pregnancy, and medication use.
1. General principles
- Reference interval — ±2SD from the mean in healthy individuals (95%).
- 5% of healthy individuals fall outside these boundaries — an isolated deviation is not always pathology.
- Biological variability: diurnal, cyclical (hormones), seasonal.
- Pre-analytical error: hemolysis, lipemia, sampling errors, prolonged tourniquet application, drawing blood from a vein distal to an IV line.
- SI units: mmol/L vs mg/dL (glucose ×18, creatinine ×0.0884).
2. Complete blood count (CBC)
| Parameter | Normal value (adults) | Clinical significance |
|---|---|---|
| Erythrocytes | M 4.0–5.5; F 3.8–5.0 ×10¹²/L | Anemia / erythrocytosis |
| Hemoglobin | M 130–170; F 120–150 g/L | < 70 — transfusion (individualized) |
| Hematocrit | M 40–50; F 36–46 % | Dehydration, polycythemia |
| MCV | 80–100 fL | < 80 — microcytic; > 100 — megaloblastic |
| MCH | 27–33 pg | Hypo-/hyperchromia |
| RDW | 11,5–14,5 % | Anisocytosis ↑ in iron deficiency |
| Reticulocytes | 0,5–2 % | Bone marrow regeneration |
| Leukocytes | 4–9 ×10⁹/L | Infection, hemoblastosis |
| — neutrophils | 47–72 % | Left shift — bacterial infection |
| — lymphocytes | 19–37 % | Viral, lymphoproliferation |
| — eosinophils | 0,5–5 % | Allergy, parasitosis |
| — basophils | 0–1 % | CML |
| — monocytes | 3–11 % | Chronic infections, TB |
| Platelets | 150–400 ×10⁹/L | < 50 — bleeding risk |
| ESR | M up to 15; F up to 20 mm/h | Non-specific inflammation marker |
3. Biochemistry — proteins and nitrogenous wastes
- Total protein: 65–85 g/L.
- Albumin: 35–50 g/L (hepatic synthesis; ↓ in nephrotic syndrome, cirrhosis, sepsis).
- Globulins: 20–35 g/L; A/G ratio 1.5–2.5.
- Urea: 2.5–8.3 mmol/L.
- Creatinine: M 62–106; F 44–88 µmol/L. Used in GFR formulas (CKD-EPI).
- Uric acid: M 210–420; F 150–350 µmol/L (gout > 420).
- Cystatin C: 0.6–0.95 mg/L (more accurate GFR marker in the elderly).
4. Liver function tests
| Parameter | Normal | Clinical significance |
|---|---|---|
| ALT | < 40 IU/L | Hepatocellular injury |
| AST | < 40 IU/L | Liver, myocardium, muscles |
| AST/ALT (de Ritis ratio) | 0,8–1,3 | > 2 — alcoholic hepatitis, cirrhosis |
| GGT | M < 55; F < 38 U/L | Cholestasis, alcohol |
| ALP | 40–150 U/L (adults) | Cholestasis, bone pathology |
| Total bilirubin | 3.4–20.5 µmol/L | > 34 — jaundice |
| — direct | up to 5 µmol/L | Cholestasis, hepatic |
| — indirect | up to 15 µmol/L | Hemolysis, Gilbert syndrome |
| INR/PT | 0,8–1,2 | Liver synthetic function |
| Albumin | 35–50 g/L | Chronic liver failure |
5. Lipid profile
- Total cholesterol: < 5.2 mmol/L.
- LDL-C: < 3.0 mmol/L in healthy individuals; < 1.4 in very high CV risk (ESC 2019).
- HDL-C: M > 1.0; F > 1.3 mmol/L.
- TG: < 1.7 mmol/L; > 10 — risk of pancreatitis.
- Non-HDL-C = TC − HDL-C; potent predictor of CV risk.
- ApoB — best surrogate of atherogenic particles, < 100 mg/dL in healthy individuals.
- Lp(a) — inherited, > 50 mg/dL (125 nmol/L) = increased risk.
6. Carbohydrates and kidneys
- Fasting glucose: 3.3–5.5 mmol/L (venous plasma).
- HbA1c: < 6.0% (WHO); diabetes diagnosis ≥ 6.5%; target < 7.0% in most diabetic patients.
- Fasting insulin: 2–25 µIU/mL; HOMA-IR = insulin × glucose / 22.5 < 2.7.
- Creatinine + age + sex → eGFR (CKD-EPI 2021, without race coefficient).
- CKD by eGFR: G1 > 90, G2 60–89, G3a 45–59, G3b 30–44, G4 15–29, G5 < 15 (RRT).
- Urine albumin-to-creatinine ratio (ACR): A1 < 30; A2 30–300; A3 > 300 mg/g.
7. Electrolytes and ABG
| Parameter | Normal | Critical |
|---|---|---|
| Na⁺ | 135–145 mmol/L | < 120 or > 160 |
| K⁺ | 3.5–5.0 mmol/L | < 2.5 or > 6.5 |
| Cl⁻ | 98–107 mmol/L | — |
| Total Ca²⁺ | 2.15–2.55 mmol/L | > 3.5 (hypercalcemic crisis) |
| Ionized Ca²⁺ | 1.15–1.30 mmol/L | More accurate |
| Mg²⁺ | 0.7–1.05 mmol/L | ↓ tetany, arrhythmias |
| P (phosphate) | 0.8–1.45 mmol/L | CKD ↑ |
| pH | 7,35–7,45 | < 7.2 or > 7.6 |
| PaCO₂ | 35–45 mmHg | > 60 hypercapnia |
| HCO₃⁻ | 22–26 mmol/L | — |
| PaO₂ | 75–100 mmHg | < 60 respiratory failure |
| Lactate | < 2 mmol/L | > 4 — severe hypoperfusion |
8. Cardiac Biomarkers
- Troponin I/T (high-sensitivity hs-cTn): 99th percentile usually < 14–19 ng/L. 0/1h and 0/3h diagnostic algorithm (ESC 2023).
- Dynamics: ↑ at 3–4 h, peak at 12–24 h, normalization in 7–10 days.
- CK-MB: < 24 U/L; becoming obsolete, inferior to troponin.
- Myoglobin: rapid rise (1–3 h), but non-specific.
- NT-proBNP: < 125 pg/mL (age < 75); > 450 — screen for heart failure in young adults, > 900 (under 75 years), > 1800 (≥ 75 years) — supports acute heart failure.
- D-dimer: < 500 ng/mL (age-adjusted rule = age × 10 for > 50 years).
9. Coagulation Panel
- Prothrombin time (PT): 11–15 s; INR 0.8–1.2.
- aPTT: 25–35 s.
- Fibrinogen: 2–4 g/L; < 1 — bleeding risk, > 4 — acute-phase response.
- D-dimer: fibrin degradation product; ↑ in VTE, DIC, pregnancy, sepsis.
- Antithrombin III: 80–120 %; deficiency indicates thrombophilia.
- Protein C, S — deficiency indicates thrombosis.
- Anti-Xa — monitoring of LMWH (target 0.6–1.0 U/mL), direct Xa inhibitors (conditionally).
- Thromboelastography (TEG/ROTEM) — dynamic assessment of coagulation.
10. Inflammation and Immunology
- CRP: < 5 mg/L; hs-CRP for cardiovascular risk: < 1 low, 1–3 intermediate, > 3 high.
- Procalcitonin: < 0.1 ng/mL — no bacterial infection; > 0.5 — probable; > 2 — septic shock likely.
- ESR: non-specific, but useful for monitoring rheumatic diseases.
- Ferritin: M 30–400; F 15–150 ng/L. ↓ iron deficiency anemia; ↑ inflammation, hemochromatosis, hemophagocytic syndrome.
- IL-6: < 7 pg/mL; ↑ sepsis, COVID, rheumatoid arthritis.
- Immunoglobulins: IgG 7–16, IgA 0.7–4, IgM 0.4–2.3 g/L.
11. Key Hormones
- TSH: 0.4–4.0 mIU/L (in pregnant women 0.1–2.5).
- Free T4: 9–22 pmol/L.
- Morning cortisol: 170–540 nmol/L.
- Prolactin: M 73–407; non-pregnant F 102–496 mIU/L.
- Aldosterone/renin ratio: ARR > 30 — screening for primary hyperaldosteronism.
- PTH: 15–65 pg/mL.
- 25-(OH)-vitamin D: > 30 ng/mL (75 nmol/L) — normal.
- hCG: < 5 mIU/mL outside of pregnancy; doubles every 48 h in the 1st trimester.
12. FAQ
Why is troponin elevated in pulmonary embolism, myocarditis, and sepsis?
Troponin elevation is non-specific for ACS—it is a marker of cardiomyocyte necrosis of any etiology. It is interpreted in the context of clinical presentation and ECG.
How to differentiate mild anemia from normal values taking age into account?
In elderly patients (> 65), Hb < 120 g/L (WHO) is already classified as anemia; the cause must always be investigated (GI bleeding, malignancy, CKD).
What is a "panic value" and is the laboratory technician obliged to call?
Yes. The list of critical values is regulated by clinical and diagnostic service protocols; the laboratory technician calls the ordering physician within 15–30 minutes.
Why is creatinine imperfect for GFR estimation?
It depends on muscle mass (in elderly individuals or sarcopenia, it may mask a true decline in GFR). Cystatin C is more accurate.
How to differentiate in vitro hemolysis from true hemolysis?
In vitro hemolysis: ↑ K⁺, LDH, AST — without clinical symptoms. True hemolysis: ↓ haptoglobin, ↑ indirect bilirubin, ↑ LDH, ↓ Hb, ↑ reticulocytes.
See also: Anemias · Myocardial Infarction · CKD · Coagulopathies · Propaedeutics Catalog