Pemeriksaan Darah

01Foundational Principles and the Medicolegal Framework

The forensic examination of blood sits at the intersection of clinical medicine and the law. In Indonesia, the legal basis for forensic blood examination rests primarily on Article 133 of the KUHAP (Kitab Undang-Undang Hukum Acara Pidana / Criminal Procedure Code), which empowers an investigator to formally request a doctor to perform medical examination on victims, suspects, or cadavers for cases involving injury, poisoning, or death. The results of this examination are documented in a Visum et Repertum (VeR), a sworn written medico-legal report. Under Article 184(1) KUHAP, the VeR holds the status of documentary evidence (alat bukti surat) and carries the same evidentiary weight as other forms of legal evidence in court proceedings.

A critical concept for the exam is the sequential approach to forensic blood analysis. This is not random; it follows a strict hierarchy from general detection to individual identification. The test-writer expects you to know the order and to understand why each step must precede the next. The sequence is:

1. Is this substance blood at all? (Presumptive tests)

2. Is this confirmed to be blood? (Confirmatory crystal tests)

3. Is this human blood? (Species determination / precipitin test)

4. Which blood group does it belong to? (ABO, Rh, and other systems)

5. Who does this blood belong to? (DNA analysis / individualization)

Each question can only be answered once the preceding question has been resolved. You cannot skip to DNA analysis without first establishing that the sample is indeed blood.

02Classification of Forensic Blood Tests

03Detailed Walkthrough of the Forensic Blood Examination

3.1 Presumptive Tests: "Is it blood?"

Presumptive tests are screening tools. They are highly sensitive (meaning they detect tiny amounts of blood) but not very specific (meaning they can produce false positives). Their purpose is to narrow down which stains at a crime scene warrant further, more expensive analysis. They work on a common principle: the heme group in hemoglobin has peroxidase-like activity, meaning it catalyzes oxidation-reduction reactions that produce a visible color change or luminescence.

Kastle-Meyer (Phenolphthalein) Test is the most widely used presumptive test today. The reagent contains reduced phenolphthalin. When applied to a bloodstain and followed by hydrogen peroxide, the heme group catalyzes oxidation of phenolphthalin back to phenolphthalein, producing a pink color. This is the test you should default to in exam questions asking about field screening.

Benzidine Test was historically the most sensitive presumptive color test. It produces a blue-green color in the presence of blood. However, benzidine is a confirmed Group 1 human carcinogen (bladder cancer) classified by IARC, and its routine laboratory use has been banned or restricted in many jurisdictions. On the exam, benzidine frequently appears as a distractor. If a question asks about the "safest" or "currently recommended" presumptive test, do not pick benzidine.

Luminol Test is uniquely useful because it can detect trace amounts of blood that have been cleaned, diluted, or are invisible to the naked eye. It reacts with the iron in hemoglobin to produce a blue-white chemiluminescence visible in a darkened room. It is the test of choice for crime scene searching when blood may have been washed away. A drawback is that certain metal ions (copper, iron salts) and plant peroxidases (horseradish) can produce false positives.

High-yield false positive triggers include: strong oxidants (bleach, hypochlorite), metal salts (copper, nickel), plant peroxidases (horseradish, potato), and hydrogen peroxide-containing products. Conversely, strong reductants like lithium and zinc can cause false negatives (rare).

3.2 Confirmatory Tests: "Is this definitely blood?"

If a presumptive test is positive, the next step is a confirmatory (microcrystal) test. These tests form characteristic crystals from the heme molecule, providing a more reliable identification.

Teichmann Test (developed by Ludwig Teichmann, 1850s): The dried blood sample is treated with glacial acetic acid and a chloride salt (NaCl) and gently heated. The heme group oxidizes and incorporates the halide to form hemin (ferriprotoporphyrin IX chloride). Under microscopy, you see small, brown/dark, rhomboid-shaped crystals arranged singly or in clusters. This test works on samples up to several years old.

Takayama Test (developed by Masaeo Takayama, 1912): The blood sample is treated with a reagent containing pyridine, glucose, and sodium hydroxide. Pyridine reacts with the heme iron to form pyridine ferroprotoporphyrin (hemochromogen). Under microscopy, you see pink/salmon, feathery, needle-like crystals arranged in clusters or sheaves. This test is generally considered more reliable than the Teichmann test because it works under milder conditions and is less affected by the age or contamination of the sample.

The exam loves to test the distinction between these two crystal tests. Remember:

• Teichmann = Brown rhomboid = Hemin = Acidic conditions

• Takayama = Pink feathery = Hemochromogen = Alkaline conditions (NaOH)

3.3 Species Determination: "Is this human blood?"

Once confirmed as blood, the next question is whether it is human blood. This step is critical in criminal investigations involving both humans and animals.

Precipitin (Ring) Test is the classic test. Anti-human serum (obtained by immunizing a rabbit with human serum proteins) is placed in a test tube. A saline extract of the suspected bloodstain is carefully layered on top. If the blood is human, a white ring of precipitate forms at the interface of the two solutions within minutes. This occurs because the anti-human antibodies bind to human blood proteins (antigens), forming visible antigen-antibody complexes.

Ouchterlony Double Immunodiffusion is a variation where anti-human serum is mixed into an agar gel plate. Wells are punched, and different antigen samples are placed in them. If the blood is human, a precipitin arc (band) forms between the antigen well and the surrounding antibody-containing gel. This method is useful when multiple unknown samples need to be tested simultaneously.

Modern immunochromatographic assays (lateral flow, similar in concept to a pregnancy test) can identify human-origin hemoglobin or glycophorin A and are faster and simpler to use, but the precipitin test remains the most commonly tested concept on exams.

3.4 Blood Grouping: "Which blood group?"

Once human origin is confirmed, the blood is typed using antigen systems. The ABO system and Rh system are the two most tested and clinically significant systems.

ABO System (Landsteiner, 1901):

For liquid blood, forward typing (adding known antisera to the patient's RBCs) and reverse typing (adding known RBCs to the patient's serum) are standard.

For dried bloodstains, the standard method is the Absorption-Elution technique (introduced by Vittorio Siracusa, 1923). In this method, known antibodies are applied to the dried stain. Antibodies corresponding to the antigen in the stain are absorbed (bound). Unbound antibodies are washed away. The absorbed antibodies are then released (eluted) by heating, and the eluate is tested against known indicator RBCs for agglutination. This is the best method to determine blood group from a dried stain and is a favorite test point.

Rh System: The D antigen is the most immunogenic. Rh-positive individuals carry the D antigen; Rh-negative individuals lack it. Two inheritance theories are frequently tested:

04Forensic Blood Alcohol Determination

4.1 Clinical and Legal Significance

Blood alcohol concentration (BAC) testing is one of the most frequently encountered forensic blood tests in clinical practice, particularly for traffic-related offenses and assault cases. In Indonesia, the primary traffic statute is UU No. 22 Tahun 2009 (UU LLAJ) concerning Road Traffic and Transportation. Article 283 penalizes anyone who operates a motor vehicle under conditions that disturb concentration, which explicitly includes alcohol influence. Notably, unlike many Western countries (e.g., the US at 0.08%, Germany at 0.05%), Indonesia does not have a codified numerical BAC threshold for driving impairment. Instead, clinical assessment and forensic evidence together support the determination of impairment in court.

4.2 Dubowski's Stages of Alcohol Influence

This table, originally published by Kurt Dubowski in 1957 and updated through 2012, is a cornerstone of forensic toxicology testing. You must know the stages and their corresponding BAC ranges.

Note the overlapping BAC ranges between stages. This is intentional: tolerance varies by individual. Chronic heavy drinkers may appear clinically sober at BAC levels that would incapacitate naive drinkers.

4.3 Widmark Formula

The Widmark equation is the standard medicolegal formula for estimating BAC from a known drinking history, or for retrograde extrapolation (back-calculating BAC at the time of an incident).

$$C=\frac{A}{r\times W}-(\beta \times t)C\; =\; \backslash frac\{A\}\{r\; \backslash times\; W\}\; -\; (\backslash beta\; \backslash times\; t)$$

Where:

The Widmark factor ($rr$) is lower in females because women have a higher proportion of body fat (fat is largely water-free), meaning alcohol distributes into a smaller volume of body water, resulting in a higher BAC for the same amount consumed.

Alcohol elimination follows zero-order kinetics in the postabsorptive phase. This means the body eliminates a fixed amount of alcohol per hour regardless of the concentration, unlike most drugs that follow first-order kinetics. This is a frequently tested concept.

4.4 Specimen Collection for BAC

A critical preanalytical point: when collecting blood for forensic BAC determination, the skin must not be swabbed with alcohol-based antiseptics (ethanol, isopropanol). Instead, non-alcoholic disinfectants (e.g., povidone-iodine, aqueous chlorhexidine) must be used. Using an alcohol swab can contaminate the sample and produce a falsely elevated BAC, which is a common trap question. The preferred anticoagulant is sodium fluoride (NaF) with potassium oxalate, as NaF inhibits glycolysis by RBCs and microbial fermentation, both of which could otherwise produce ethanol in vitro and falsely raise the BAC.

05Forensic Paternity Testing

Forensic blood examination plays a central role in disputed paternity cases. The principle is that a child's blood group antigens must be inherited from the parents. If a putative father lacks the alleles necessary to produce a child's blood type, he is excluded from paternity.

The exam typically presents a vignette with a mother, child, and putative father's blood types and asks whether paternity is excluded. The principle to apply:

• A child cannot possess an antigen that neither parent carries.

• A child must inherit one allele from each parent.

• If the alleged father cannot provide the allele the child has (and the mother did not provide it), paternity is excluded.

Example: Mother is group O ($I^O{I}^{O}I^OI^O$), child is group B ($I^B{I}^{O}I^BI^O$). The child's $I^{B}I^B$ allele must come from the father. If the alleged father is group O ($I^O{I}^{O}I^OI^O$), he cannot be the biological father. He is excluded.

DNA analysis using Short Tandem Repeats (STR) via Polymerase Chain Reaction (PCR) is now the gold standard for paternity testing and individualization. While blood group testing can only exclude a putative father, DNA testing can both exclude and include with probability values exceeding 99.99%.

06Differential Diagnosis and Distractors

07Traps and High-Yield Pearls

The most common trap on this topic is confusing the hierarchy of forensic blood tests. Students frequently jump to DNA or blood grouping without recognizing that the exam vignette is asking about an earlier step in the sequence. If the question stem describes an unknown reddish stain at a crime scene and asks for the "first step" or "next best step," the answer is a presumptive test (Kastle-Meyer or luminol), not a crystal test, not a precipitin test, and certainly not DNA.

A second common pitfall involves the Widmark formula. Students often forget that the $rr$ factor differs between males and females, or they fail to account for the time variable ($\beta \times t\backslash beta\; \backslash times\; t$). A question might describe a scenario where a suspect drank a known quantity hours before an incident and ask you to calculate or estimate the BAC at the time of the event. If you forget to subtract the elimination term, you will overestimate the BAC.

Third, do not confuse specimen collection rules. Questions about BAC sample collection are designed to test whether you know that alcohol-based skin antiseptics are prohibited and that NaF/potassium oxalate is the preservative of choice to prevent in vitro alcohol generation. Forgetting this can lead you to the wrong answer on a question about specimen handling.

Fourth, regarding the Indonesian legal framework: the VeR is classified as documentary evidence (alat bukti surat) under Article 184 KUHAP, not as expert testimony. However, if the doctor who wrote the VeR is called to testify in court, that oral testimony then carries the status of expert testimony (keterangan ahli). The distinction between the written document and the in-court testimony of its author is a commonly tested legal nuance.

Finally, remember that in paternity testing, blood group analysis can only exclude paternity. It can never prove it. If the alleged father's blood group is consistent with paternity, it means he could be the father, along with all other individuals who share that blood group. Only DNA analysis provides the statistical certainty required for positive identification.