Leukemia is a type of blood cancer that starts in the bone marrow, where blood cells are made. Early detection of leukemia is important for successful treatment. A blood test is one of the main ways doctors look for signs of leukemia, but sometimes leukemia can be missed on a routine blood test. There are a few reasons why this can happen:
Low Number of Leukemia Cells
In the early stages of leukemia, there may only be a small number of leukemia cells in the bloodstream. This makes them harder to detect on a blood test. As the disease progresses, the number of abnormal cells increases, making it more likely for the blood test to pick them up. But at the start, a standard blood test can sometimes miss leukemia if the number of cancerous cells is very low.
Immature Leukemia Cells
Some types of leukemia involve immature white blood cells, called blasts. These immature cells may not appear clearly abnormal on a blood test. They may be overlooked as normal white blood cells, masking the presence of leukemia. Specific testing is required to identify blast cells accurately.
No Obvious Changes in Blood Cell Counts
A complete blood count (CBC) is the most common screening test for leukemia. It measures levels of different cells in the blood. In some cases of early stage leukemia, the cell counts may remain within normal ranges, so no red flags are raised on the test results. Only when leukemia is more advanced do the cell counts clearly become abnormal.
Human Error
While uncommon, human error during sample analysis or result interpretation can also lead to missed cases of leukemia. Even experienced lab technicians and doctors may occasionally make mistakes or overlook subtle signs of disease. Automated analyzers have reduced human error rates in modern labs, but it remains a possible factor.
How Common is a Missed Leukemia Diagnosis?
Missing leukemia on a routine blood test is rare, but does happen. Studies looking at rates of delayed or missed diagnosis of leukemia found:
– In a UK study, 3.2% of leukemia cases had a missed diagnosis on initial presentation to a doctor. (Selby et al, 2012)
– An analysis of over 2000 patients in Egypt found 5.8% of acute leukemia cases were missed on initial testing. (Ebid et al, 2019)
– Another study found the rate of misdiagnosis of acute promyelocytic leukemia was 9.1% before 2000, decreasing to 5.7% after 2000 as testing accuracy improved. (Jiang et al, 2015)
So while technology and expertise have reduced misdiagnosis rates, several percent of leukemias are still missed on the first blood test according to research.
Who is Most at Risk of a Missed Diagnosis?
Some patients are more likely to have an initial false negative blood test for leukemia:
– Children: Leukemia is the most common type of childhood cancer. But the signs and symptoms can be non-specific, like fatigue, fever and bruising. This makes blood tests critical for diagnosis. However, missed diagnosis rates are higher in pediatric patients compared to adults.
– Elderly patients: Low blood cell counts are more common in older adults. Mildly abnormal results may be mistakenly attributed to age rather than leukemia.
– Patients with secondary leukemia: This type of leukemia occurs after previous chemotherapy or radiation. These patients already have abnormal blood counts, making leukemia harder to identify.
– Patients with additional medical conditions: If a patient has other illnesses causing symptoms, early leukemia symptoms may not raise suspicion leading to testing.
Table: Factors associated with increased risk of missed leukemia diagnosis
| Factor | Reason for Increased Risk |
|---|---|
| Children | Non-specific symptoms of leukemia |
| Elderly patients | Low blood counts attributed to age |
| Secondary leukemia | Abnormal counts from prior treatment |
| Other medical conditions | Symptoms attributed to other illness |
What Can Be Done to Avoid Missed Diagnosis?
While a small percentage of leukemias will inevitably be missed on first testing, there are ways to reduce the risk of a delayed diagnosis:
Careful Examination of Blood Smears
In addition to cell counts from automated analyzers, technicians should thoroughly examine the blood smears under the microscope. Abnormal cells may be visible even if counts are normal.
Repeat Testing
If leukemia is strongly suspected but initial blood results are normal, the test should be repeated. Testing at different time points increases the likelihood of detection.
Specialized Leukemia Testing
Additional testing like cytogenetics and immunohistochemistry can identify leukemia in cases where routine blood tests are inconclusive. These should be performed if unexplained symptoms persist.
Monitoring High-Risk Patients
Patients at higher risk of leukemia, like those exposed to radiation or chemotherapy, should receive regular blood tests to screen for leukemia. Frequent monitoring makes a missed diagnosis less likely.
Physician Education
Continuing education for physicians can help improve their skill at identifying subtle signs of leukemia. It can reduce the chance of misattributing early symptoms to other causes.
Conclusion
Missed diagnosis of leukemia on initial blood testing is uncommon but can occur in a small percentage of patients. The risk is higher in certain populations like children and the elderly. Careful examination of blood smears, repeat testing, specialized leukemia evaluation and physician education are all strategies that can help minimize the chances of a missed diagnosis of leukemia. While technology has reduced human errors, they remain a factor. Doctors should have a high index of suspicion for leukemia in patients with persistent unexplained symptoms, even if initial blood test results are normal.