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PA13.{2,4} | Approach to Anemia & Lab Investigation — PBL Case

CLINICAL SETTING

Mahesh, a 24-year-old agricultural labourer from a tribal district in Odisha, walks four kilometres to the weekly outreach camp of the Primary Health Centre. He complains of progressive weakness and breathlessness on exertion for six months — he can no longer work a full day in the paddy fields. He also admits to eating mud occasionally (pica) and has noticed his nails have become 'spoon-shaped'. He is vegetarian and survives largely on rice and pulses. The PHC medical officer, Dr Priya, has a basic haematology analyser available. She draws 4 mL of blood into an EDTA tube and orders a CBC, and asks the health worker to prepare a peripheral blood smear. The automated report arrives but raises several questions about interpretation, and Dr Priya decides to use the case as a teaching opportunity for the two interns posted to the camp.

Trigger 1: Mahesh Arrives at the Camp

Mahesh's vitals: pulse 108/min, BP 96/64 mmHg, RR 22/min. He is thin, pale, with angular cheilitis, koilonychia, and a smooth tongue. His abdomen is soft; no organomegaly. The medical officer notes that his stool shows hookworm ova on microscopy. She explains to the interns that before ordering a single test, they need to classify the anaemia systematically. She asks them: 'Tell me what you think the MCV will show, and why.'

DISCUSSION POINTS

How is anaemia defined according to WHO criteria? What is the threshold haemoglobin value for an adult male, and how would you grade the severity once you have the result?
Before the blood count returns, which morphological class of anaemia would you predict for Mahesh, and what clinical features support this prediction?
Mahesh eats mud (pica) and has koilonychia and a smooth tongue. What is the significance of each of these findings in terms of iron status?
What is the single most important etiological question to answer after establishing the morphological class — and what findings in this patient's history guide your answer?

Click to reveal Trigger 2: The Blood Count Arrives — and Raises More Questions (discuss previous trigger first!)

Trigger 2: The Blood Count Arrives — and Raises More Questions

The automated CBC result: Hb 6.4 g/dL, RBC 3.1 × 10¹²/L, MCV 64 fL, MCH 20 pg, MCHC 27 g/dL, RDW 21%, WBC 7,800/µL, Platelets 410,000/µL, Reticulocyte count 1.1%. The health worker has prepared a peripheral smear and stained it with Leishman stain. It shows hypochromic microcytic red cells, pencil cells, and occasional target cells. The DLC performed by counting 100 WBCs shows: Neutrophils 62%, Lymphocytes 28%, Monocytes 7%, Eosinophils 3%. One intern notices the DLC was counted at the feather edge of the smear and is concerned the differential may be inaccurate.

DISCUSSION POINTS

Apply the 5-step diagnostic workup framework to Mahesh's CBC: confirm anaemia, grade severity, determine morphological class, calculate the Reticulocyte Production Index, and state what the RPI tells you about the bone marrow's response.
The intern counted the DLC at the feather edge. Explain why this is a systematic error, what it would do to the neutrophil and eosinophil counts, and where on the smear a DLC should be performed.
The peripheral smear shows pencil cells and target cells. What does each morphological feature represent in terms of defective haemoglobin synthesis?
Mahesh's eosinophil count is 3%. Given his stool findings, is this a relevant observation? How does hookworm infection contribute to microcytic anaemia mechanistically?

Click to reveal Trigger 3: Confirming the Diagnosis and Planning at the PHC Level (discuss previous trigger first!)

Trigger 3: Confirming the Diagnosis and Planning at the PHC Level

Dr Priya confirms the diagnosis of severe iron deficiency anaemia secondary to chronic hookworm infestation. She initiates oral ferrous sulphate 200 mg TDS and albendazole. She explains to the interns that the haematology analyser must be quality-controlled daily before patient samples, and that the correct order of draw and tube selection are not administrative trivialities — they directly affect result accuracy. She asks the interns to prepare a one-page QC and collection checklist for the PHC.

DISCUSSION POINTS

Hb estimation by cyanmethemoglobin method is the gold standard. Describe the principle: what reagent is used, at what wavelength is absorbance measured, and what is the main advantage over Sahli's method at this PHC level?
Explain how to perform a manual WBC count using a Neubauer haemocytometer: which reagent is used for dilution, what dilution factor, which squares are counted, and what formula gives WBCs per mm³?
Dr Priya sets up morning QC before starting patient samples. What is the purpose of running three control levels (low, normal, high), and what is the 'delta check'? Why is a delta check clinically important for Mahesh's follow-up samples?
Four weeks after starting iron therapy, Mahesh's Hb is 8.1 g/dL and his reticulocyte count is 9.8%. Is this the expected response? Explain what is happening in the bone marrow at this point and predict what the peripheral smear would look like now.

Group Task Assignments

Group 1: WHO anaemia definition and morphological-etiological classification

Construct a classification table of anaemia using two axes: morphological (MCV-based: microcytic, normocytic, macrocytic) and etiological (decreased production, increased destruction, blood loss). Populate each cell with at least two diagnoses and one distinguishing lab finding.
Apply both classification axes to Mahesh's case. Identify the single most common cause of microcytic anaemia in adult males in rural India and explain the mechanism.

Competencies: PA13.2

Group 2: Reticulocyte Production Index — calculation and interpretation

Using Mahesh's reticulocyte count of 1.1% and haematocrit of 19%, calculate the corrected reticulocyte count and the Reticulocyte Production Index. State the maturation factor used and justify it.
Interpret the RPI: is this a hypoproliferative or hyperproliferative picture? Explain what this tells you about the bone marrow's aetiology of anaemia — and contrast it with the expected RPI in a patient four weeks into iron therapy.

Competencies: PA13.2

Group 3: Manual haematology techniques — Hb, RBC count, WBC count

Step through the cyanmethemoglobin (Drabkin's) method for Hb estimation: reagent components, reaction mechanism, wavelength, normal CV, and two pre-analytical conditions that can give a falsely elevated reading.
Demonstrate the Neubauer haemocytometer calculation for WBC count: reagent, dilution, squares counted, formula. Calculate the WBC count if 96 cells are counted in the four corner squares with a 1:20 dilution.

Competencies: PA13.4

Group 4: Peripheral smear preparation and DLC technique

Describe the correct technique for spreading a peripheral blood smear (drop size, angle, speed), the correct zone for DLC counting, and the systematic scanning path (battlement/meander method). Explain why neutrophils concentrate at the feather edge.
A DLC is performed by counting 100 cells. The technician counts at the feather edge and reports neutrophils 78%, eosinophils 1%. The correct DLC zone would show neutrophils 62%, eosinophils 3%. Explain the error mechanism and its clinical consequence in Mahesh's case.

Competencies: PA13.4

Group 5: Quality control and PHC-level haematology workflow

Design a morning QC checklist for the PHC haematology analyser: three control level checks, Levey-Jennings chart interpretation, acceptable SD limits, and the corrective action if a control is out of range.
Describe the 'delta check' concept: what is compared, the typical threshold for flagging, and a clinical scenario at a PHC where a delta check prevents a dangerous error (e.g., a patient whose Hb suddenly drops by 3 g/dL without clinical explanation — what pre-analytical causes must be ruled out before accepting the result).

Competencies: PA13.4

Learning Issues

Research these questions and bring your findings to the discussion.

[PA13.2] How is anaemia defined, classified (morphological and etiological), and systematically investigated using a 5-step framework incorporating the MCV, reticulocyte production index, and targeted confirmatory tests?
[PA13.4] How are haemoglobin (cyanmethemoglobin method), RBC count, WBC count, and differential leucocyte count performed manually, and what pre-analytical and technical errors affect accuracy of each test?