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Diagnostic Tests and Lab Reports: Understanding Your Results

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Hereditary spherocytosis (HS) is diagnosed through a combination of blood tests. A standard Complete Blood Count (CBC) often shows a high MCHC level. The modern gold standard for confirming an HS diagnosis is the EMA-binding test, which is more accurate than older osmotic fragility tests.

Key Takeaways

  • • A high MCHC and high RDW on a standard Complete Blood Count are often the first laboratory clues of hereditary spherocytosis.
  • • A peripheral blood smear allows pathologists to visually identify spherocytes, which are small, round red blood cells missing their normal pale center.
  • • The EMA-binding test is the modern gold standard for confirming an HS diagnosis, largely replacing the less accurate osmotic fragility test.
  • • A DAT (Coombs test) is a necessary step to rule out autoimmune hemolytic anemia, which can mimic the appearance of hereditary spherocytosis under a microscope.
  • • Genetic testing via Next-Generation Sequencing (NGS) may be used to confirm a diagnosis in newborns, cases with no family history, or when standard test results are borderline.

Diagnosing Hereditary Spherocytosis (HS) is a process of “connecting the dots” between physical symptoms, family history, and specific laboratory markers. Because other conditions can mimic HS, doctors use a tiered approach to ensure an accurate diagnosis for you or your child [1][2].

The First Clues: The CBC and Blood Smear

The journey usually begins with a Complete Blood Count (CBC), a standard blood test that measures the different types of cells in the blood. In HS, two specific markers often stand out:

  • High MCHC (Mean Corpuscular Hemoglobin Concentration): This measures how “packed” or dense the hemoglobin is inside each red blood cell. In HS, cells are dehydrated and small, making the MCHC unusually high (typically above 36 g/dL) [3][4].
  • High RDW (Red Cell Distribution Width): This indicates a wide variation in the size of the red blood cells, which is common as the body tries to replace destroyed cells with new ones [5][6].

Next, a pathologist performs a peripheral blood smear, where they look at the blood under a microscope. They are searching for spherocytes—small, dark, perfectly round red blood cells that lack the pale center of a normal cell [7][8]. They also look for reticulocytosis, which is an increase in young red blood cells (reticulocytes), showing the bone marrow is working hard to compensate for cell loss [9][4].

Confirming the Diagnosis: The EMA-Binding Test

While the older Osmotic Fragility (OF) test was used for decades, it is no longer the preferred method. The OF test measures how easily cells burst in salt water, but it often gives “false positives” because other conditions can also make cells fragile [10][11].

The modern “gold standard” is the Flow Cytometric EMA-binding test [12][13].

  • How it works: A special dye (Eosin-5-maleimide) binds to the proteins on the surface of red blood cells.
  • Why it’s better: It is much more specific than the old tests. Because HS cells have fewer of these surface proteins, they “glow” less under a specialized laser (flow cytometer) [14][15]. This test is highly accurate and can even detect HS in patients who have already had their spleen removed [16][14].

When is Genetic Testing (NGS) Needed?

Next-Generation Sequencing (NGS) is a highly detailed test that looks directly at the DNA blueprints for red blood cell proteins [17][18]. While not always necessary, it is used when:

  • Standard tests like the EMA-binding test are borderline or inconclusive [17][19].
  • The patient is a newborn or infant, where typical markers are harder to see [20][21].
  • There is no family history of the condition [17].
  • The doctor suspects a “double diagnosis,” such as HS combined with Gilbert Syndrome or Thalassemia [18][22].

Rule-Out: Autoimmune Hemolytic Anemia (AIHA)

A critical step is distinguishing HS from Autoimmune Hemolytic Anemia (AIHA), a condition where the immune system mistakenly attacks healthy red blood cells [20][23]. Both conditions show spherocytes on a blood smear.
To tell them apart, doctors use the Direct Antiglobulin Test (DAT), also known as the Coombs test [24][25].

  • A Positive DAT usually means the problem is immune-related (AIHA).
  • A Negative DAT points toward a structural problem like HS [24][20].

Lab Report Completeness Checklist

When reviewing lab results, ensure you have the following information:

  1. Hemoglobin Level: To check for the degree of anemia [2].
  2. Reticulocyte Count: To see how fast the body is making new blood [4].
  3. MCHC: To check for cell density (values >36 g/dL are significant) [3].
  4. Bilirubin (Total and Indirect): To measure the level of jaundice [2].
  5. EMA-Binding Result: The definitive confirmation test [12].
  6. DAT/Coombs Result: To rule out immune-mediated destruction [24].

Frequently Asked Questions

Why is the EMA-binding test preferred over the osmotic fragility test?
The EMA-binding test is highly specific and accurate for diagnosing hereditary spherocytosis. The older osmotic fragility test is no longer preferred because it often gives false positive results when other conditions make red blood cells fragile.
What does a high MCHC mean on my CBC blood test?
MCHC measures how densely packed the hemoglobin is inside your red blood cells. A high MCHC is a strong indicator of hereditary spherocytosis because the abnormal cells are dehydrated and smaller than normal red blood cells.
Why does the doctor need to do a DAT or Coombs test?
The DAT or Coombs test is used to rule out an immune system condition called autoimmune hemolytic anemia. This is crucial because both conditions cause round red blood cells (spherocytes), but a negative DAT result confirms the issue is structural, like HS, rather than an immune attack.
When is genetic testing needed to diagnose hereditary spherocytosis?
Genetic testing is not always required, but it is very helpful if standard blood tests like the EMA-binding test are inconclusive. It is also used for infants, when there is no family history of the condition, or if the doctor suspects you might have multiple blood disorders.

Questions for Your Doctor

  • • Why do you recommend the EMA-binding test over the older osmotic fragility test for us?
  • • Was a Direct Antiglobulin Test (DAT/Coombs) performed, and was it negative?
  • • My or my child's MCHC is high on the CBC; how does this specifically point toward HS in our case?
  • • If our EMA-binding test results are borderline, would Next-Generation Sequencing (NGS) be the next logical step to confirm the diagnosis?

Questions for You

  • • Is there a known history of 'thin blood,' early gallbladder surgery, or enlarged spleens in my parents, siblings, or extended family?
  • • Do I have a copy of the most recent CBC and the 'differential' (the breakdown of cell types) to bring to the hematologist?

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This page explains diagnostic tests and lab reports for hereditary spherocytosis for educational purposes only. Always consult your hematologist or primary care physician to interpret your specific laboratory results.

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