From the Guidelines
The tests mentioned (total bilirubin, direct bilirubin, indirect bilirubin, PT, PTT, and FOBT) can help evaluate certain causes of anemia but are not primary tests for diagnosing anemia itself, which is primarily diagnosed using complete blood count (CBC) tests that measure hemoglobin, hematocrit, and red blood cell indices, as recommended by the British Society of Gastroenterology guidelines for the management of iron deficiency anaemia in adults 1.
Anemia Diagnosis and Evaluation
Anemia is defined as a haemoglobin (Hb) concentration below the lower limit of normal for the relevant population and laboratory performing the test, with a strong recommendation to define anaemia based on this criterion 1. The tests mentioned can provide valuable information about potential causes of anemia.
- Bilirubin tests (total, direct, and indirect) can help identify hemolytic anemia, where elevated indirect bilirubin suggests increased red blood cell destruction.
- PT (prothrombin time) and PTT (partial thromboplastin time) assess coagulation and can help identify bleeding disorders that might cause blood loss anemia.
- FOBT (fecal occult blood test) detects hidden blood in stool, which can indicate gastrointestinal bleeding as a cause of iron deficiency anemia.
Comprehensive Anemia Workup
For a comprehensive anemia workup, these tests should be combined with CBC, iron studies (serum iron, ferritin, TIBC), vitamin B12, folate levels, and reticulocyte count, as iron deficiency should be confirmed by iron studies prior to investigation, with serum ferritin being the single most useful marker of IDA 1. The pattern of abnormalities across these tests helps determine the specific type and cause of anemia, guiding appropriate treatment. In patients with chronic kidney disease (CKD), the investigation and management of anaemia is complex, and iron deficiency is a major element, but multiple other mechanisms may also contribute towards the development of anaemia, hence the requirement for detailed haematological investigation 1.
From the Research
Laboratory Tests for Anemia
The following laboratory tests can help determine anemia in a patient:
- Total bilirubin: Elevated levels can indicate hemolytic anemia, as seen in patients with spur cell anemia 2
- Direct bilirubin: Can be used to differentiate between conjugated and unconjugated hyperbilirubinemia, which can be useful in diagnosing anemia 3
- Indirect bilirubin: Can be used to diagnose and monitor hemolytic anemia, as it is often elevated in these cases 3
- Prothrombin Time (PT) and Partial Thromboplastin Time (PTT): Can be used to evaluate the coagulation pathway and detect any abnormalities that may be contributing to anemia 2
- Fecal Occult Blood Test (FOBT): Can be used to detect occult blood loss, which can be a cause of iron deficiency anemia 4
Relationship Between Laboratory Tests and Anemia
The relationship between these laboratory tests and anemia is complex, and a comprehensive evaluation is necessary to determine the underlying cause of anemia. For example:
- Elevated bilirubin levels can indicate hemolytic anemia, but can also be seen in other conditions such as liver disease 2, 3
- Abnormal PT and PTT results can indicate a coagulation disorder, which can be a cause of anemia 2
- A positive FOBT result can indicate occult blood loss, which can be a cause of iron deficiency anemia 4
Clinical Applications
These laboratory tests can be used in various clinical settings to diagnose and monitor anemia, including: