What is hemoglobin (Hb) detection?

Hemoglobin (Hb) Detection

Hemoglobin detection refers to the laboratory measurement of hemoglobin concentration in blood, primarily used to diagnose anemia, assess oxygen-carrying capacity, and identify hemoglobin variants or abnormalities. 1, 2

Primary Detection Methods

Standard Laboratory Measurement

• Hemoglobin concentration is most commonly measured using automated hematology analyzers as part of a complete blood count (CBC), which is the recommended first-step test. 3
• The cyanmethemoglobin method (Evelyn-Malloy spectrophotometric method) is the gold standard, measuring hemoglobin by converting it to cyanmethemoglobin and detecting absorbance changes at specific wavelengths. 1, 4
• Hemoglobin is preferred over hematocrit because it is more reproducible across laboratories and not affected by storage time or patient variables like serum glucose. 3
• Normal hemoglobin values are <13 g/dL in men and <12 g/dL in non-pregnant women, with values below these thresholds indicating anemia. 1, 3

Point-of-Care and Field Methods

• Digital hemoglobinometers (such as TrueHb) provide rapid screening with sensitivity of 74-82% and specificity >75%, making them suitable for outreach settings. 5
• Paper-based assays using Drabkin reagent and color analysis can measure hemoglobin with accuracy within 1 g/dL in 90.7% of cases, useful in resource-limited settings. 6
• Non-invasive devices (such as TouchHb) exist but have lower diagnostic accuracy (positive likelihood ratio 1.5) compared to invasive methods. 5

Specialized Hemoglobin Detection

Methemoglobin (MetHb) Detection

• MetHb levels are measured using co-oximetry in blood gas analyzers, detecting the change in absorbance at 630 nm when cyanide converts MetHb to cyan-MetHb. 1
• Normal blood contains <1% MetHb, with levels >1.5 g/dL causing visible cyanosis. 1
• MetHb measurement is critical for diagnosing methemoglobinemia, where ferric iron (Fe³⁺) replaces normal ferrous iron (Fe²⁺), causing functional anemia without actual hemoglobin decrease. 1

Hemoglobin Variant Detection

• Hemoglobin electrophoresis at pH 7.1 identifies structural variants such as HbM variants caused by mutations in alpha-, beta-, or gamma-globin genes. 1
• Targeted DNA sequencing of globin genes is the gold standard for confirming hemoglobin variants, being technically simpler and more specific than electrophoresis. 1
• HbH disease (β₄ tetramers) is detected by hemoglobin electrophoresis showing HbH presence and peripheral blood smear revealing HbH inclusion bodies. 7, 8

Clinical Context and Interpretation

When to Measure Hemoglobin

• Hemoglobin measurement is essential for evaluating anemia, with investigation recommended when Hb <13 g/dL in men or <12 g/dL in women. 1
• More urgent investigation is warranted when Hb <12 g/dL in men or <10 g/dL in postmenopausal women, as lower levels suggest more serious disease. 1
• In iron deficiency anemia workup, hemoglobin should be measured alongside serum ferritin and transferrin saturation. 3

Common Pitfalls to Avoid

• Do not rely solely on hemoglobin and hematocrit for diagnosing iron deficiency, as these are late indicators that only become abnormal after iron stores are depleted. 3
• Recognize that hemoglobin measurement alone cannot distinguish between different types of anemia—additional tests (ferritin, transferrin saturation, red cell indices) are required. 3
• In patients with suspected hemoglobin variants causing cyanosis, do not assume methemoglobinemia without co-oximetry confirmation, as cardiac and pulmonary disease can also cause cyanosis. 1
• Color-based visual methods (hemoglobin color scale) have significant human interpretation errors and should be replaced with objective digital methods when possible. 5, 4