β-Hydroxybutyrate is one of the predominant ketone body forms in blood and tissues. It is commonly used to evaluate enhanced fatty acid oxidation, hepatic ketogenesis, starvation or fasting status, diabetic ketosis, exercise metabolism, and mitochondrial energy conversion. Compared with acetoacetate and acetone, β-hydroxybutyrate is present at higher concentrations in circulation and has better stability; therefore, it is widely used in blood ketone monitoring, animal models, and metabolomics research. Detection methods include β-hydroxybutyrate dehydrogenase-based enzymatic assays, test strip or blood ketone meter-based rapid detection, colorimetric or fluorometric assay kits, HPLC, and LC-MS/MS. These methods differ substantially in specificity, sensitivity, sample throughput, and metabolic interpretability.

Keywords: β-hydroxybutyrate; blood ketone detection; ketone body metabolism; β-hydroxybutyrate dehydrogenase; enzymatic detection; diabetic ketosis; fatty acid oxidation; LC-MS/MS

1 Metabolic Positioning of β-Hydroxybutyrate

1.1 Core Indicator in Ketone Body Metabolism

Ketone bodies mainly include β-hydroxybutyrate, acetoacetate, and acetone. β-Hydroxybutyrate is not strictly a ketone compound in the chemical sense, but it is usually classified as a ketone body marker in physiological and pathological research. Changes in its concentration can reflect hepatic fatty acid oxidation, ketogenesis, and the utilization of ketone bodies by peripheral tissues.

(1) Source of production

β-Hydroxybutyrate is mainly generated in hepatic mitochondria through the reduction of acetoacetate. During fasting, low-carbohydrate intake, intense exercise, insulin deficiency, or increased fatty acid supply, acetyl-CoA enters the ketogenesis pathway, leading to increased β-hydroxybutyrate levels.

(2) Tissues of utilization

The heart, skeletal muscle, kidney, and brain can use β-hydroxybutyrate as an energy substrate. The liver itself lacks the key enzyme required for ketone body utilization; therefore, it mainly produces and releases ketone bodies rather than directly oxidizing them.

(3) Redox status

The ratio between β-hydroxybutyrate and acetoacetate is influenced by the mitochondrial NADH/NAD⁺ status. Increased β-hydroxybutyrate not only indicates enhanced ketogenesis, but may also reflect changes in the mitochondrial redox state.

1.2 Differences from Acetoacetate and Acetone

(1) β-Hydroxybutyrate

β-Hydroxybutyrate is the major circulating ketone body form. Blood-based detection is more stable and is suitable for blood ketone monitoring and metabolic model evaluation.

(2) Acetoacetate

Acetoacetate is an intermediate in ketone body metabolism. It can interconvert with β-hydroxybutyrate and can also undergo non-enzymatic decarboxylation to form acetone. Some urine ketone test strips mainly reflect acetoacetate rather than β-hydroxybutyrate.

(3) Acetone

Acetone can be excreted through breath and is commonly used in breath ketone research. It is correlated with blood β-hydroxybutyrate, but the two are not fully equivalent because acetone is affected by volatility, pulmonary ventilation, and metabolic status.

Table 1 Comparison of the detection significance of ketone body indicators

2 Comparison of β-Hydroxybutyrate Detection Methods

2.1 β-Hydroxybutyrate Dehydrogenase Enzymatic Method

The β-hydroxybutyrate dehydrogenase method is one of the most commonly used methods for β-hydroxybutyrate detection. The basic principle is that β-hydroxybutyrate is converted to acetoacetate under the action of β-hydroxybutyrate dehydrogenase, while NAD⁺ is reduced to NADH. Quantification is achieved by monitoring the change in NADH absorbance or by coupling the reaction to colorimetric or fluorometric readouts.

(1) Absorbance method

This method directly monitors the change in NADH absorbance near 340 nm. It has good specificity and is suitable for standard curves and purified systems. If the sample has strong background absorbance, a sample blank should be included.

(2) Colorimetric method

A NADH-coupled chromogenic system converts the signal into visible absorbance changes, making it suitable for microplate readers and batch sample detection. The reading wavelength usually avoids 340 nm, which can reduce some instrument limitations.

(3) Fluorometric method

The fluorometric method has higher sensitivity and is suitable for detecting low concentrations of β-hydroxybutyrate, cell culture supernatants, or small-volume samples. Interference from sample autofluorescence and reducing substances should be considered.

2.2 Rapid Detection Using Blood Ketone Meters and Test Strips

Blood ketone meters are commonly used for rapid detection of β-hydroxybutyrate in whole blood. They are suitable for dynamic monitoring, time-point screening in animal experiments, and point-of-care testing in clinical settings. Their advantages are rapid operation and small sample volume, but the results depend on test strip batch, instrument calibration, and sample type.

(1) Whole blood detection

Blood ketone meters are mostly used for whole blood samples such as fingertip blood or animal tail blood and are suitable for continuous time-point monitoring. Compared with enzymatic results from serum or plasma, whole blood testing may differ because of matrix differences.

(2) Dynamic monitoring

In fasting, exercise, low-carbohydrate diet, insulin treatment, or drug intervention experiments, blood ketone meters are suitable for rapidly assessing trends in β-hydroxybutyrate changes.

(3) Methodological boundaries

Blood ketone meters are suitable for rapid screening, but should not be used as the sole detection method for complex samples, tissue samples, or mechanistic studies. Key conclusions should be verified using enzymatic assays or LC-MS/MS.

2.3 HPLC and LC-MS/MS Methods

HPLC and LC-MS/MS are suitable for accurate quantification of β-hydroxybutyrate in complex samples, particularly in metabolomics, isotope tracing, and multi-metabolite analysis.

(1) HPLC method

HPLC can separate β-hydroxybutyrate through derivatization, ion-exchange chromatography, or specific chromatographic conditions. Its specificity is higher than that of conventional colorimetric methods, but sample pretreatment and method development requirements are higher.

(2) LC-MS/MS method

LC-MS/MS offers high sensitivity and specificity, and quantitative reliability can be improved by using internal standards. It is suitable for serum, plasma, tissue extracts, cell samples, and metabolic flux studies.

(3) Isotope tracing

When labeled substrates are used to study fatty acid oxidation or ketone body production, LC-MS/MS can distinguish isotopic peak patterns of β-hydroxybutyrate and further resolve metabolic sources and flux changes.

2.4 Differences Between Urine Ketone Detection and β-Hydroxybutyrate Detection

Urine ketone test strips usually mainly reflect acetoacetate and cannot be directly equated with blood β-hydroxybutyrate. During diabetic ketosis, fasting, or metabolic interventions, urine ketone results may lag behind changes in blood β-hydroxybutyrate and may also be affected by urine volume, urine dilution, and renal excretion.

Table 2 Comparison of commonly used β-hydroxybutyrate detection methods

3 Sample Types and Pretreatment

3.1 Blood Samples

Blood samples are the most commonly used sample type for β-hydroxybutyrate detection. Whole blood is suitable for rapid detection with blood ketone meters, while serum or plasma is suitable for enzymatic assays, HPLC, and LC-MS/MS.

(1) Whole blood

Whole blood testing is rapid and suitable for continuous time-point monitoring. In animal experiments, it can reduce blood collection volume, but the blood collection site, time, and instrument batch should be standardized.

(2) Serum

Serum is suitable for routine enzymatic assay kit detection. Sample separation should be performed promptly to avoid metabolite changes caused by prolonged storage at room temperature.

(3) Plasma

Plasma is suitable for metabolomics and LC-MS/MS analysis. Anticoagulant selection should be compatible with the detection method to avoid interference with enzymatic reactions or mass spectrometric signals.

3.2 Tissue Samples

Tissue β-hydroxybutyrate detection can reflect local ketone body utilization, mitochondrial metabolic status, and energy substrate switching. Common tissues include liver, heart, skeletal muscle, kidney, and brain.

(1) Rapid sampling

After tissue collection, samples should be rapidly frozen or metabolically quenched to reduce continued metabolic changes ex vivo.

(2) Homogenization conditions

The homogenization buffer should match the detection method. For enzymatic assays, strong acids, strong bases, or residual high-concentration organic solvents should be avoided because they may affect enzyme activity. For LC-MS/MS, stronger protein precipitation and metabolite extraction systems can be used.

(3) Normalization method

Tissue results can be normalized by tissue weight, protein content, or sample volume. Different normalization methods correspond to different interpretive dimensions and should not be used interchangeably.

3.3 Cell Samples and Culture Supernatants

Cell models can be used to study fatty acid oxidation, ketogenesis regulation, mitochondrial function, and changes in nutritional status. β-Hydroxybutyrate can be detected in both cell culture supernatants and intracellular extracts.

(1) Culture medium interference

Phenol red, serum, reducing components, and other metabolites in culture medium may interfere with colorimetric or fluorometric readings. Medium blanks and untreated cell controls should be included before detection.

(2) Intracellular detection

Intracellular β-hydroxybutyrate levels are usually low, requiring efficient extraction and sensitive detection. LC-MS/MS is more suitable for low-abundance or multi-metabolite analysis.

(3) Time-point selection

In fatty acid stimulation, glucose restriction, insulin treatment, and mitochondrial inhibition experiments, β-hydroxybutyrate changes are time-dependent. Early, intermediate, and endpoint detection should be incorporated into the experimental design.

Table 3 β-Hydroxybutyrate sample processing and detection considerations

4 Metabolic Significance of β-Hydroxybutyrate

4.1 Fasting, Low-Carbohydrate Intake, and Ketogenic Status

During fasting or low-carbohydrate intake, insulin levels decrease, lipolysis increases, hepatic fatty acid β-oxidation is enhanced, and acetyl-CoA enters the ketogenesis pathway, resulting in elevated blood β-hydroxybutyrate.

(1) Short-term fasting

Short-term fasting can cause mild to moderate increases in β-hydroxybutyrate. This change usually reflects a shift in energy substrate utilization from glucose toward fatty acids and ketone bodies.

(2) Long-term fasting or ketogenic diet

During long-term fasting or ketogenic diets, β-hydroxybutyrate can become an important circulating energy substrate. Results should be interpreted together with blood glucose, free fatty acids, insulin, and hepatic glycogen status.

(3) Exercise metabolism

After endurance exercise or glycogen depletion, β-hydroxybutyrate may increase. Its changes are jointly related to fatty acid mobilization, hepatic ketogenesis, and utilization by peripheral tissues.

4.2 Diabetic Ketosis and Metabolic Imbalance

When insulin is insufficient or insulin action is severely reduced, lipolysis increases and the liver produces large amounts of ketone bodies, leading to a marked increase in β-hydroxybutyrate. In this context, β-hydroxybutyrate detection reflects the current blood ketone status more accurately than urine ketone testing.

(1) Early changes

β-Hydroxybutyrate may increase before urine ketones show obvious changes. For risk assessment of hyperglycemia with ketosis, blood β-hydroxybutyrate is more direct than urine ketones.

(2) Treatment monitoring

During metabolic correction, decreased β-hydroxybutyrate can reflect reduced ketone body production and recovery of redox status. Urine ketones may lag because of changes in acetoacetate and should not be used alone for dynamic assessment.

(3) Acid-base status

Elevated β-hydroxybutyrate indicates increased ketone body burden, but the degree of acidosis must be assessed together with blood gas analysis, bicarbonate, anion gap, lactate, and related indicators.

4.3 Fatty Acid Oxidation and Mitochondrial Function

β-Hydroxybutyrate levels are closely associated with fatty acid entry into mitochondrial oxidation, ketogenesis substrate supply, and NADH/NAD⁺ status. Its changes can be used to evaluate energy substrate selection in metabolic models.

(1) Enhanced fatty acid oxidation

When fatty acid supply increases or glucose utilization decreases, elevated β-hydroxybutyrate indicates enhanced hepatic ketogenesis. If free fatty acids are also increased, enhanced lipid mobilization is further supported.

(2) Mitochondrial redox state

An increased β-hydroxybutyrate/acetoacetate ratio can indicate increased mitochondrial reductive pressure. Elevated β-hydroxybutyrate alone cannot fully distinguish increased ketogenic flux from altered redox status.

(3) Tissue-specific utilization differences

Decreased tissue β-hydroxybutyrate does not necessarily indicate reduced ketogenesis; it may also suggest enhanced ketone body uptake and oxidative utilization. Tissue results should be analyzed together with circulating levels and key enzyme expression.

4.4 Role as a Signaling Molecule

β-Hydroxybutyrate is not only an energy substrate but is also involved in epigenetic regulation, inflammation, and oxidative stress research. Its signaling effects are usually related to concentration, exposure duration, and cell type.

(1) Histone modification-related studies

β-Hydroxybutyrate can participate in epigenetic studies such as histone β-hydroxybutyrylation. Such experiments should not only measure total β-hydroxybutyrate, but should also include detection of target protein modifications.

(2) Inflammation regulation

In some studies, β-hydroxybutyrate is associated with inflammasomes, oxidative stress, and immunometabolism. Interpretation should distinguish between its role as a metabolic substrate and its role in signaling regulation.

(3) Concentration in cell models

In cell experiments, exogenous β-hydroxybutyrate concentrations should match the research question. Excessively high concentrations may introduce osmotic pressure, pH, or non-physiological metabolic burden.

Table 4 β-Hydroxybutyrate results and metabolic interpretation

5 Experimental Design and Method Selection

5.1 Routine Blood Ketone Monitoring

If the purpose is rapid assessment of blood ketone status during fasting, ketogenic diets, or animal experiments, blood ketone meters or enzymatic assay kits can be preferred. Blood ketone meters are suitable for continuous monitoring, while enzymatic assays are suitable for batch samples and standardized analysis.

(1) Animal experiments

In mouse and rat experiments, blood collection time, fasting duration, and blood collection site should be standardized. β-Hydroxybutyrate is highly sensitive to feeding status, and random sampling increases within-group variation.

(2) Clinical sample research

Serum or plasma enzymatic assays are suitable for batch sample detection. If the study involves ketosis risk, abnormal glucose metabolism, or dynamic treatment changes, blood glucose, lactate, and acid-base indicators should be measured together.

(3) Result verification

If blood ketone meter results are abnormal or inconsistent with other metabolic indicators, enzymatic assays or LC-MS/MS can be used for confirmation.

5.2 Mechanistic Studies and Metabolic Flux Analysis

Mechanistic studies should not rely solely on β-hydroxybutyrate as a single indicator. The ketogenesis pathway involves fatty acid mobilization, mitochondrial oxidation, acetyl-CoA accumulation, NADH/NAD⁺ status, and peripheral tissue utilization.

(1) Ketogenesis pathway

Key enzyme expression, including HMGCS2, HMGCL, and BDH1, can be measured to determine whether increased β-hydroxybutyrate is derived from enhanced hepatic ketogenesis.

(2) Ketone body utilization

OXCT1, ACAT1, and mitochondrial oxidative function-related indicators can be measured to determine whether peripheral tissues have enhanced ketone body oxidative utilization.

(3) Flux studies

Isotope tracing combined with LC-MS/MS can distinguish the contribution of fatty acids, glucose, or other substrates to β-hydroxybutyrate production.

5.3 β-Hydroxybutyrate Treatment in Cell Experiments

Exogenous β-hydroxybutyrate is commonly used to simulate ketone body exposure or study signaling functions. Such experiments should consider the salt form, pH, osmotic pressure, and effects on medium composition.

(1) Selection of salt form

Sodium β-hydroxybutyrate, potassium β-hydroxybutyrate, and the free acid form have different effects on medium pH and ionic composition. Isotonic or ion-matched controls should be included in cell experiments.

(2) Concentration gradient

Treatment concentrations should be set according to physiological, pathological, or model-specific conditions. Low, medium, and high doses are recommended, with monitoring of cell viability and medium pH.

(3) Time window

The time windows for β-hydroxybutyrate acting as an energy substrate and as a signaling molecule are different. Short-term treatment is suitable for observing signaling changes, whereas long-term treatment is more suitable for studies of metabolic reprogramming.

6 Common Interferences and Quality Control

6.1 Interference in Enzymatic Assays

Enzymatic assays depend on enzyme activity and coenzyme reactions. Strong reducing substances, color background, hemolysis, lipemia, or high protein concentrations in samples may interfere with results. Sample blanks should be included for both colorimetric and fluorometric methods.

(1) Sample color

Hemoglobin, phenol red in culture medium, or tissue pigments may affect absorbance readings. Phenol red-free medium or sample blank subtraction should be used when necessary.

(2) Reducing substances

NADH-related detection systems are susceptible to reducing substances. Complex samples can be confirmed using LC-MS/MS.

(3) Freeze-thaw effects

Repeated freeze-thaw cycles may alter the sample matrix and metabolite stability. All samples should be stored in aliquots, and the number of freeze-thaw cycles should be standardized.

6.2 LC-MS/MS Quality Control

When detecting β-hydroxybutyrate by LC-MS/MS, internal standards, matrix effects, recovery, and standard curve linearity should be carefully controlled. Extraction efficiency is particularly important for tissue and cell samples.

(1) Internal standards

Stable isotope-labeled internal standards can correct for pretreatment loss and ionization differences. Without internal standards, quantitative reliability decreases.

(2) Matrix effects

Serum, tissue, and culture medium matrices differ substantially. Linearity, recovery, and dilution reliability should be validated separately for different sample types.

(3) Batch control

Samples should be randomized during analysis, and quality control samples should be included. Instrument drift should be evaluated for large sample batches.

Table 5 Common problems and control strategies in β-hydroxybutyrate detection

7 Related Reagent and Material Selection

Table 6 Core reagent selection for β-hydroxybutyrate detection and metabolic research

8 Frequently Asked Questions

8.1 Why may β-hydroxybutyrate and urine ketone results be inconsistent?

Urine ketone test strips usually mainly detect acetoacetate, whereas blood β-hydroxybutyrate reflects the major circulating ketone body form. In early ketosis or during treatment, β-hydroxybutyrate and acetoacetate may change asynchronously; therefore, urine ketone testing cannot fully replace blood β-hydroxybutyrate detection.

8.2 Can a blood ketone meter replace laboratory enzymatic assays?

Blood ketone meters are suitable for rapid dynamic monitoring, but they are not suitable for complex samples or mechanistic studies. If precise quantification, batch comparison, or publication-level data support is required, enzymatic assay kits or LC-MS/MS should be used for validation.

8.3 Does increased β-hydroxybutyrate always indicate diabetic ketosis?

No. Fasting, ketogenic diets, intense exercise, low-glucose states, and enhanced fatty acid oxidation can all increase β-hydroxybutyrate. Whether it represents pathological ketosis should be determined together with blood glucose, acid-base status, anion gap, and the clinical or experimental model context.

8.4 What should be considered when adding β-hydroxybutyrate in cell experiments?

The salt form, pH, osmotic pressure, and treatment concentration should be considered. Sodium β-hydroxybutyrate may alter the sodium ion concentration in culture medium, whereas the free acid form may affect pH; therefore, ion or pH controls should be included.

8.5 Does β-hydroxybutyrate detection require fasting samples?

If basal circulating levels are being studied, feeding status should generally be controlled. β-Hydroxybutyrate is sensitive to fasting, feeding, and circadian rhythm; sampling time and fasting conditions should be standardized across experimental groups.

8.6 How should enzymatic assays and LC-MS/MS be selected?

Enzymatic assays can be selected for routine batch testing of serum, plasma, or tissue samples. LC-MS/MS should be selected for complex samples, multi-metabolite analysis, isotope tracing, or method confirmation. If the results of the two methods are inconsistent, sample matrix and pretreatment differences should be examined first.

8.7 What is the significance of the β-hydroxybutyrate/acetoacetate ratio?

This ratio can reflect the mitochondrial redox state and is particularly related to the NADH/NAD⁺ balance. If only β-hydroxybutyrate is measured, it is difficult to distinguish increased ketogenic flux from altered redox status.

β-Hydroxybutyrate detection methods should be selected according to the research objective. Blood ketone meters are suitable for rapid dynamic monitoring, enzymatic assays are suitable for routine quantification and batch samples, and LC-MS/MS is suitable for complex samples, multi-analyte analysis, and metabolic flux studies.