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🩸 Blood Grouping (ABO & Rh Typing)
What is a Blood Group?
A blood group refers to genetically encoded antigens present on the surface of red blood cells (RBCs), as well as on leukocytes, platelets, and plasma proteins. Most blood group genes are inherited autosomally following Mendelian codominance — meaning both alleles are expressed.
— Henry's Clinical Diagnosis and Management by Laboratory Methods
How Blood Group is Determined
Blood grouping is performed in two complementary steps:
1. Forward Typing (Cell Grouping)
- A 3–5% RBC suspension from the patient is tested with commercial anti-A and anti-B antisera
- Agglutination (clumping) indicates the presence of that antigen on the cell surface
- Most labs use monoclonal antisera derived from hybridoma cell lines
2. Reverse (Back) Typing (Serum Grouping)
- The patient's serum is tested against reagent RBCs of known A₁ and B phenotype
- Detects the expected ABO antibodies in the patient's serum
- Results of forward and reverse typing must agree before a blood group is reported
ABO Group Interpretation Table
| Blood Group | RBC Antigens | Serum Antibodies |
|---|---|---|
| A | A antigen | Anti-B |
| B | B antigen | Anti-A |
| AB | A + B antigens | Neither |
| O | Neither | Anti-A + Anti-B |
Rh (D) Typing
- The D antigen (RhD) is the most immunogenic blood group antigen (~70% of Rh-negative individuals exposed to D-positive blood will form anti-D)
- Tested separately: Rh-positive (D+) or Rh-negative (D−)
ABO Grouping Discrepancies — When Results Don't Match
Forward and reverse types may conflict due to:
| Category | Cause |
|---|---|
| Unexpected positive RBC reactions | Acquired B antigen (colon/gastric cancer), cold autoantibodies |
| Unexpected positive serum reactions | Rouleaux (plasma expanders), room-temperature alloantibodies (anti-M, N, P1) |
| Unexpected negative RBC reactions | Weak subgroups (A₂, A₃), disease-associated antigen depression |
| Unexpected negative serum reactions | Age extremes (neonates, elderly), immunodeficiency, immunosuppression |
AABB Standards require two separate determinations of a recipient's ABO group before transfusion — either from historical records or a second sample. — Henry's Clinical Diagnosis and Management by Laboratory Methods, p. 846
🔬 Abnormal Constituents Found in Urine (Urinalysis)
Normal urine contains water, urea, creatinine, electrolytes, and small amounts of protein. The presence of the following substances in abnormal amounts signals disease:
1. Proteinuria (Protein)
- Normal: <150 mg/day (trace)
- Abnormal presence indicates: Glomerulonephritis, nephrotic syndrome, diabetic nephropathy, hypertensive kidney disease, multiple myeloma (Bence Jones protein)
- Types: Glomerular (albumin), tubular (small proteins), overflow (immunoglobulin light chains)
2. Glucosuria (Glucose)
- Normal: Absent (renal threshold ~180 mg/dL blood glucose)
- Abnormal presence indicates: Diabetes mellitus, renal glycosuria (normal blood glucose, low renal threshold), Fanconi syndrome
3. Ketonuria (Ketones)
- Normal: Absent
- Abnormal presence indicates: Diabetic ketoacidosis (DKA), starvation, prolonged vomiting, alcoholic ketoacidosis, high-fat/low-carb diets
4. Hematuria (Blood/RBCs)
- Normal: 0–2 RBCs/HPF
- Abnormal presence indicates: Urinary tract infection, renal stones, glomerulonephritis, trauma, bladder/renal tumors, anticoagulant therapy
5. Hemoglobinuria
- Free hemoglobin in urine (without intact RBCs)
- Indicates: Intravascular hemolysis — mismatched blood transfusion, hemolytic anemia, malaria (blackwater fever)
6. Bilirubinuria (Bilirubin)
- Normal: Absent (conjugated bilirubin only passes into urine)
- Abnormal presence indicates: Obstructive jaundice, hepatocellular disease (hepatitis, cirrhosis)
7. Urobilinogenuria
- Small amounts normal; increased in hemolytic anemia, liver disease; absent in complete biliary obstruction
8. Pyuria (WBCs/Pus)
- Normal: <5 WBCs/HPF
- Abnormal presence indicates: Urinary tract infection (UTI), pyelonephritis, interstitial nephritis, tuberculosis of the kidney
9. Casts
| Cast Type | Significance |
|---|---|
| Hyaline | Normal in small amounts; concentrated urine |
| RBC casts | Glomerulonephritis (hallmark) |
| WBC casts | Pyelonephritis, interstitial nephritis |
| Granular casts | Tubular damage, chronic renal disease |
| Waxy casts | Advanced chronic kidney disease |
| Fatty casts | Nephrotic syndrome |
10. Microorganisms (Bacteria, Fungi)
- Bacteriuria: UTI (significant if >10⁵ CFU/mL in midstream sample)
- Candiduria: Candida UTI, often in diabetics or immunocompromised patients
11. Crystals
| Crystal | Associated Condition |
|---|---|
| Uric acid | Gout, tumor lysis syndrome |
| Calcium oxalate | Ethylene glycol poisoning, hyperoxaluria |
| Cystine | Cystinuria (genetic disorder) |
| Struvite (triple phosphate) | Infection with urease-producing bacteria |
12. Myoglobinuria
- Myoglobin (from muscle) in urine — indicates rhabdomyolysis (crush injury, severe exercise, statin toxicity)
Summary Table: Abnormal Urinary Constituents
| Substance | Normal | Abnormal Finding Suggests |
|---|---|---|
| Protein | Trace | Nephropathy, myeloma |
| Glucose | Absent | Diabetes, Fanconi |
| Ketones | Absent | DKA, starvation |
| Blood (RBCs) | 0–2/HPF | UTI, stones, tumor |
| Bilirubin | Absent | Liver/biliary disease |
| WBCs | <5/HPF | Infection, nephritis |
| RBC casts | Absent | Glomerulonephritis |
| Bacteria | Absent | UTI |
Key Point: Blood group determination requires both forward and reverse typing to be valid. A single test is never sufficient for transfusion decisions. For urine, abnormal constituents are detected by dipstick (chemical), microscopy, and culture — each targeting different pathological processes.
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