Basic investigation course :-
Basic investigation course:- CBC , LFT, KFT , .what to see every parameter and how to interpret diagnosis according to investigation. Explain in detail
Reading File
Finding Sources
Finding Sources
Finding Sources
Finding Sources
Finding Sources
Finding Sources
Finding Sources
Finding Sources
Finding Sources
Reading File
Reading File
I now have solid textbook content. Let me compile the comprehensive answer from my medical knowledge, textbook references, and the retrieved content.
Basic Investigation Course: CBC, LFT & KFT — Complete Interpretation Guide
PART 1 — COMPLETE BLOOD COUNT (CBC)
The CBC is a panel that evaluates the three major cell lines produced by the bone marrow: red blood cells (RBCs), white blood cells (WBCs), and platelets.
🔴 RED BLOOD CELL PARAMETERS
1. Hemoglobin (Hb)
| Reference Range | Male: 13.5–17.5 g/dL | Female: 12.0–15.5 g/dL |
|---|
What to see: The oxygen-carrying capacity of blood.
| Finding | Interpretation |
|---|---|
| Low Hb (Anemia) | < 13.5 M / < 12.0 F → Anemia |
| Mild: 10–12 g/dL | Nutritional (iron, B12, folate deficiency), chronic disease |
| Moderate: 7–10 g/dL | Hemolysis, renal failure, bone marrow suppression |
| Severe: < 7 g/dL | Aplastic anemia, severe hemolysis, major blood loss |
| High Hb (Polycythemia) | > 17.5 M / > 15.5 F |
| True polycythemia | Polycythemia vera, high altitude, COPD, dehydration |
2. Hematocrit (HCT / PCV — Packed Cell Volume)
- Normal: Male 41–53% | Female 36–46%
- Mirrors Hb × 3 (rule of thumb)
- Low: anemia; High: polycythemia, dehydration
3. RBC Count
- Normal: 4.5–5.5 × 10⁶/μL (M), 4.0–5.0 × 10⁶/μL (F)
- Combined with Hb and MCV helps classify anemia type
4. MCV — Mean Corpuscular Volume (KEY PARAMETER)
- Normal: 80–100 fL
| MCV | Type | Common Causes |
|---|---|---|
| < 80 fL | Microcytic anemia | Iron deficiency anemia (most common), Thalassemia, Sideroblastic anemia, Lead poisoning |
| 80–100 fL | Normocytic anemia | Acute blood loss, hemolysis, anemia of chronic disease, renal failure, aplastic anemia |
| > 100 fL | Macrocytic anemia | Vitamin B12 deficiency, Folate deficiency, Hypothyroidism, Liver disease, Alcohol, Drugs (methotrexate, hydroxyurea) |
5. MCH — Mean Corpuscular Hemoglobin
- Normal: 27–33 pg
- Low MCH → hypochromic (iron deficiency, thalassemia)
- High MCH → hyperchromic (B12/folate deficiency)
6. MCHC — Mean Corpuscular Hemoglobin Concentration
- Normal: 32–36 g/dL
- Low MCHC → hypochromia (iron deficiency)
- High MCHC → hereditary spherocytosis (classic finding)
7. RDW — Red Cell Distribution Width
- Normal: 11.5–14.5%
- High RDW = anisocytosis (varied RBC sizes)
- Iron deficiency → High RDW + Low MCV (helps differentiate from thalassemia trait where RDW is normal)
⚪ WHITE BLOOD CELL PARAMETERS
Total WBC Count
- Normal: 4,000–11,000 cells/μL
| Finding | Clinical Significance |
|---|---|
| Leukocytosis (> 11,000) | Infection (bacterial), inflammation, leukemia, stress, steroids |
| Leukopenia (< 4,000) | Viral infection, bone marrow suppression, SLE, aplastic anemia, HIV |
Differential Count (Absolute & %)
| Cell | Normal % | Raised (Causes) | Low (Causes) |
|---|---|---|---|
| Neutrophils | 50–70% | Bacterial infection, MI, burns, steroids, CML | Viral infection, SLE, drug toxicity, aplastic anemia (Neutropenia → sepsis risk) |
| Lymphocytes | 20–40% | Viral infection (EBV, CMV), TB, CLL, lymphoma | HIV/AIDS, immunosuppression, steroid therapy |
| Monocytes | 2–8% | TB, infective endocarditis, malaria, chronic infection | Rare |
| Eosinophils | 1–4% | Allergies, asthma, parasitic infections, Addison's disease | Steroid use, acute infection |
| Basophils | 0–1% | CML (very characteristic), hypothyroidism, allergic reactions | Anaphylaxis, hyperthyroidism |
Key patterns:
- Left shift (band neutrophils > 10%) → Severe bacterial infection, sepsis
- Atypical lymphocytes → Infectious mononucleosis (EBV)
- Blast cells → Acute leukemia (medical emergency)
🟡 PLATELET PARAMETERS
Platelet Count
- Normal: 150,000–400,000 /μL
| Finding | Threshold | Causes |
|---|---|---|
| Thrombocytopenia (Low) | < 150,000 | ITP, DIC, dengue fever, heparin-induced (HIT), hypersplenism, aplastic anemia, SLE |
| Bleeding risk significant | < 50,000 | |
| Spontaneous hemorrhage risk | < 20,000 | |
| Thrombocytosis (High) | > 400,000 | Reactive (infection, iron deficiency, post-splenectomy), Essential thrombocythemia |
Mean Platelet Volume (MPV)
- Normal: 7.5–12.5 fL
- High MPV + low count → ITP (large young platelets being released)
- Low MPV + low count → Bone marrow failure, aplastic anemia
PART 2 — LIVER FUNCTION TESTS (LFT)
LFTs assess different aspects of liver function: hepatocellular integrity, synthetic function, and biliary excretion. — Harper's Illustrated Biochemistry, 32nd Ed.
🟠 BILIRUBIN
Total Bilirubin
- Normal: 0.2–1.2 mg/dL
- Jaundice visible clinically when > 2.5 mg/dL
| Type | Normal | High Indicates |
|---|---|---|
| Indirect (Unconjugated) | 0.2–0.8 mg/dL | Pre-hepatic: Hemolysis (sickle cell, thalassemia, G6PD), Gilbert's syndrome, neonatal jaundice |
| Direct (Conjugated) | 0.0–0.3 mg/dL | Post-hepatic (obstructive): Gallstones, cholangiocarcinoma, pancreatic cancer, PSC/PBC; also hepatocellular disease |
Pattern Recognition:
| Pattern | Bilirubin Type Elevated | Diagnosis |
|---|---|---|
| Predominantly unconjugated | Hemolysis / Gilbert's syndrome | |
| Predominantly conjugated | Biliary obstruction / intrahepatic cholestasis | |
| Both raised equally | Hepatocellular disease (hepatitis, cirrhosis) |
🟠 LIVER ENZYMES
ALT (Alanine Aminotransferase)
- Normal: 7–56 U/L (M slightly higher)
- Most liver-specific enzyme
- ALT elevation = hepatocyte damage
AST (Aspartate Aminotransferase)
- Normal: 10–40 U/L
- Less specific — also elevated in heart, skeletal muscle, kidneys
AST:ALT Ratio — CRITICAL INTERPRETIVE TOOL
| Ratio | Interpretation |
|---|---|
| AST:ALT > 2:1 | Alcoholic hepatitis (hallmark finding) |
| AST:ALT < 1 (ALT dominant) | Viral hepatitis, NAFLD, drug-induced liver injury |
| Massive elevation (> 1000 U/L both) | Acute viral hepatitis, ischemic hepatitis ("shock liver"), acetaminophen toxicity |
— Harrison's Principles of Internal Medicine 22E; Harper's Biochemistry 32nd Ed.
ALP (Alkaline Phosphatase)
- Normal: 44–147 U/L
- Elevated in: Biliary obstruction (cholestasis), bone disease (Paget's, metastases), pregnancy
- Markedly elevated ALP + minimally elevated transaminases → Cholestatic pattern (stones, stricture, cancer)
GGT (Gamma-Glutamyl Transferase)
- Normal: 8–61 U/L (M), 5–36 U/L (F)
- Very sensitive for alcohol use and biliary disease
- If ALP high + GGT high → confirms liver (not bone) origin of ALP elevation
- Isolated GGT elevation → Chronic alcohol use
🟠 LIVER SYNTHETIC FUNCTION
Serum Albumin
- Normal: 3.5–5.0 g/dL
- Half-life ~20 days → reflects chronic liver synthetic function
- Low albumin → Cirrhosis, chronic hepatitis, malnutrition, nephrotic syndrome (protein loss)
Prothrombin Time (PT) / INR
- Normal PT: 11–13 sec | INR: 0.8–1.2
- Liver makes clotting factors I, II, V, VII, IX, X
- PT/INR prolonged → Acute liver failure (sensitive early marker), cirrhosis, Vitamin K deficiency
- In acute liver failure: PT is the most sensitive marker of hepatic synthetic failure
Total Protein
- Normal: 6.0–8.3 g/dL
- = Albumin + Globulins
- Low total protein with low albumin → Liver disease / malnutrition
- Low albumin with high globulins → Cirrhosis, chronic infection, autoimmune hepatitis
LFT Pattern Summary Table
| Pattern | ALT/AST | ALP/GGT | Bilirubin | Albumin/PT | Diagnosis |
|---|---|---|---|---|---|
| Hepatocellular | ↑↑↑ | Normal/slightly ↑ | Both ↑ | ↓ (if severe) | Viral hepatitis, drug toxicity, alcohol |
| Cholestatic | Normal/mild ↑ | ↑↑↑ | Conjugated ↑↑ | Normal early | Biliary obstruction, cholangitis |
| Mixed | ↑↑ | ↑↑ | Both ↑ | ↓ | PBC, PSC, drug reactions |
| Cirrhosis (chronic) | Mild ↑ or normal | Mild ↑ | ↑ | ↓↓ | Low albumin, prolonged PT — chronic damage |
PART 3 — KIDNEY FUNCTION TESTS (KFT)
KFT evaluates the ability of the kidneys to filter, excrete, and regulate. — Textbook of Family Medicine 9e; Comprehensive Clinical Nephrology 7th Ed.
🔵 BLOOD UREA NITROGEN (BUN)
- Normal: 7–18 mg/dL (2.5–6.4 mmol/L)
- Urea is the end product of protein catabolism (made in liver, excreted by kidneys)
- Elevated BUN is NOT specific to kidney disease alone
| Cause of High BUN | Mechanism |
|---|---|
| Pre-renal (most common) | Dehydration, heart failure, GI bleeding, burns, decreased renal perfusion |
| Intrinsic renal | Glomerulonephritis, AKI, CKD |
| Post-renal | Urinary obstruction (BPH, stones, tumors) |
| Non-renal | High protein diet, corticosteroids, hypercatabolism |
| Low BUN | Severe liver disease (can't make urea), malnutrition, SIADH |
🔵 SERUM CREATININE
- Normal: 0.6–1.2 mg/dL (M), 0.5–1.1 mg/dL (F)
- Product of muscle metabolism; directly reflects GFR when stable
- More specific than BUN for true renal dysfunction
Key points:
- Creatinine rises late — up to 50% of nephrons can be lost before creatinine rises above normal range
- Affected by: muscle mass (low in elderly, malnourished → may mask renal impairment), diet (high meat intake raises it), drugs (cimetidine, trimethoprim block secretion, falsely raise creatinine)
Creatinine in CKD Staging (rising creatinine → falling GFR in parabolic fashion):
- Small drop in GFR at high baseline = small creatinine rise
- Small drop in GFR at already reduced baseline = large creatinine rise — Textbook of Family Medicine 9e
🔵 BUN:CREATININE RATIO — GOLD STANDARD DIFFERENTIATOR
| Ratio | Interpretation |
|---|---|
| 10:1 (Normal) | Intrinsic renal disease (e.g., acute tubular necrosis) |
| > 20:1 | Pre-renal (dehydration, heart failure) OR Post-renal (obstruction) |
| < 10:1 | Low protein intake, severe liver disease, SIADH |
— Textbook of Family Medicine 9e; Comprehensive Clinical Nephrology 7th Ed.
🔵 eGFR (Estimated Glomerular Filtration Rate)
- Calculated using serum creatinine + age + sex (CKD-EPI or MDRD equation)
- Normal: > 90 mL/min/1.73m²
- Most labs now auto-report eGFR alongside creatinine
| eGFR (mL/min/1.73m²) | CKD Stage | Action |
|---|---|---|
| ≥ 90 | Stage 1 (normal or high, with kidney damage) | Monitor if proteinuria present |
| 60–89 | Stage 2 (mildly decreased) | Monitor |
| 45–59 | Stage 3a (mild-moderate) | Nephrology referral consideration |
| 30–44 | Stage 3b (moderate-severe) | Nephrology referral |
| 15–29 | Stage 4 (severe) | Prepare for renal replacement therapy |
| < 15 | Stage 5 (kidney failure/ESRD) | Dialysis or transplant |
🔵 SERUM ELECTROLYTES (Often reported with KFT)
Sodium (Na⁺)
- Normal: 136–145 mEq/L
- Hyponatremia (< 136): SIADH, heart failure, cirrhosis, hypothyroidism, over-hydration
- Hypernatremia (> 145): Dehydration, diabetes insipidus, excessive sodium intake
Potassium (K⁺)
- Normal: 3.5–5.0 mEq/L
- Hypokalemia (< 3.5): Diuretics, vomiting, diarrhea, Conn's syndrome, alkalosis
- ECG changes: flattened T waves, U waves → can cause fatal arrhythmias
- Hyperkalemia (> 5.0): Renal failure (most common), ACE inhibitors, Addison's disease, acidosis, rhabdomyolysis
- ECG changes: peaked T waves, wide QRS → medical emergency if > 6.5
Uric Acid
- Normal: 3.5–7.2 mg/dL (M), 2.6–6.0 mg/dL (F)
- Elevated (hyperuricemia): Gout, renal failure, tumor lysis syndrome, diuretics
- Low: Liver disease, Wilson's disease
🔵 URINE OUTPUT / URINALYSIS (assessed alongside KFT)
- Oliguria: < 400 mL/day → AKI concern
- Proteinuria: Glomerular disease (nephrotic syndrome if > 3.5 g/day)
- Hematuria: Glomerulonephritis, UTI, stones, malignancy
- Urine sodium < 20 mEq/L → Pre-renal (kidneys conserving sodium)
- Urine sodium > 40 mEq/L → Intrinsic renal (tubular dysfunction)
INTEGRATED CLINICAL APPROACH
When CBC + LFT + KFT Are Ordered Together:
| Clinical Scenario | CBC | LFT | KFT |
|---|---|---|---|
| Jaundice | Hemolytic anemia? | ↑ Bilirubin pattern | Usually normal |
| Sepsis | Leukocytosis, left shift, thrombocytopenia (DIC) | Elevated transaminases (ischemic) | Rising creatinine (septic AKI) |
| Cirrhosis | Pancytopenia (hypersplenism), macrocytosis | ↑ Bilirubin, ↑ PT, ↓ Albumin, mild ↑ ALT | Often AKI in decompensation (hepatorenal syndrome) |
| CKD | Normocytic normochromic anemia (low EPO) | Usually normal | ↑ Creatinine, ↑ BUN, ↓ eGFR, hyperkalemia |
| Dengue fever | Leukopenia, thrombocytopenia (< 100,000) | Elevated AST > ALT | Usually normal, can develop AKI |
| SLE | Leukopenia, hemolytic anemia, thrombocytopenia | ANA-associated hepatitis | Lupus nephritis → proteinuria, ↑ creatinine |
| Drug toxicity (e.g., paracetamol) | Normal initially | Massive ↑ ALT/AST (> 1000), ↑ PT | Hepatorenal syndrome in severe cases |
| Malaria | Anemia, thrombocytopenia | ↑ Indirect bilirubin (hemolysis), ↑ LFTs | AKI in severe/falciparum malaria |
| TB | Normocytic anemia, lymphocytosis, ↑ ESR | ↑ LFTs (drug-induced or hepatic TB) | Usually normal |
QUICK REFERENCE: Normal Ranges Summary
| Test | Parameter | Normal Range |
|---|---|---|
| CBC | Hb (M/F) | 13.5–17.5 / 12.0–15.5 g/dL |
| WBC | 4,000–11,000 /μL | |
| Neutrophils | 50–70% | |
| Lymphocytes | 20–40% | |
| Platelets | 150,000–400,000 /μL | |
| MCV | 80–100 fL | |
| LFT | Total Bilirubin | 0.2–1.2 mg/dL |
| Direct Bilirubin | 0.0–0.3 mg/dL | |
| ALT | 7–56 U/L | |
| AST | 10–40 U/L | |
| ALP | 44–147 U/L | |
| GGT | 8–61 U/L (M) | |
| Albumin | 3.5–5.0 g/dL | |
| Total Protein | 6.0–8.3 g/dL | |
| PT/INR | 11–13 sec / 0.8–1.2 | |
| KFT | BUN | 7–18 mg/dL |
| Creatinine (M/F) | 0.6–1.2 / 0.5–1.1 mg/dL | |
| BUN:Cr ratio | 10–20:1 | |
| eGFR | > 90 mL/min/1.73m² | |
| Na⁺ | 136–145 mEq/L | |
| K⁺ | 3.5–5.0 mEq/L | |
| Uric acid (M/F) | 3.5–7.2 / 2.6–6.0 mg/dL |
Sources: Harper's Illustrated Biochemistry 32nd Ed; Textbook of Family Medicine 9e; Comprehensive Clinical Nephrology 7th Ed; Harrison's Principles of Internal Medicine 22E (2025); Kaplan & Sadock's Synopsis of Psychiatry.
This is a shared conversation. Sign in to Orris to start your own chat.