Prealbumin: The clinical utility and analytical methodologies

Abstract

Prealbumin is a small protein which has been widely evaluated as a nutritional and a prognostic marker. The small size and concentration of prealbumin in blood proposes challenges on measuring it with high sensitivity and specificity. Over the years, a number of analytical methodologies have been developed, which may help establish prealbumin as a useful biomarker in routine clinical practice. The aim of the short review was to explore the current literature on the clinical utility of prealbumin and the advances made in the analytical methodologies of prealbumin. We searched MEDLINE, EMBASE and the Cochrane Library for articles published between January 1980 and July 2019, with the general search terms of ‘prealbumin’, ‘prognostic marker’, ‘nutritional marker’, ‘analytical methodologies’ and ‘malnutrition’. Additionally, we selected relevant articles and comprehensive overviews from reference lists of identified studies. The routine use of prealbumin in clinical practice remains debatable; however; it can complement clinical history, anthropometric assessment and physical examination to assess malnutrition with more certainty. Consensus on the clinical applications of prealbumin in the management of malnutrition is warranted.

Background

Prealbumin is a 55 kDa homotetrameric protein, which can be found mainly in blood, but also in cerebrospinal fluids and eyes. The majority of prealbumin is synthesized in the liver, but to a lesser extent in choroid plexus, retinal pigment epithelium and pancreas. ¹ Prealbumin is also known as transthyretin due to its dual transport property of thyroid hormone, either as thyroxine (T₄) or triiodothyronine (T₃) and holo-retinol-binding protein (holo-RBP) which is the RBP and Vitamin A complex. ²

It has a shorter circulating half-life, averaging 2.5 days ³ compared with the 19–21 days of albumin which makes it superior in assessing short-term nutritional changes in the body. The gene coding for prealbumin is located on chromosome 18 q12.1 and at present, more than 100 genetic variants of prealbumin have been identified. Interestingly, this protein undergoes multiple posttranslational modifications. ⁴ It is found that the genetic mutations associated with such modifications result in different proteoforms of prealbumin and are crucial in producing prealbumin-associated diseases such as hereditary amyloid polyneuropathy and Alzheimer’s disease. ⁵

Prealbumin has been evaluated widely as a marker of the nutritional status and refeeding status, and a marker of disease prognosis. In this short review, we will discuss the significance of prealbumin in the above contexts as well as the currently available analytical methods and their limitations in measuring this small protein.

Prealbumin as a nutritional marker

Since the 1970s, prealbumin has been considered as a biochemical indicator of protein-energy malnutrition (PEM). In uncomplicated PEM, there is a reduction in body nitrogen pools and an adaptive suppression of hepatic protein synthesis – an adaptive change reliably detected by serial prealbumin measurements. ⁶ In body composition studies, prealbumin is closely correlated with fluctuations of lean body mass and is thought to be the only plasma protein which has this correlation.^7,8 Additionally, favourable characteristics such as short biological half-life, richness in tryptophan which gives it a high degree of reactivity to protein status ⁸ and the highest essential to non-essential amino acids ratio ¹ make prealbumin an optimal predictor of nutritional status in the body.

While it is a sensitive marker of nutritional status, prealbumin concentrations need to be interpreted carefully within the clinical context, as it is a negative acute phase reactant. Its concentration in blood can temporarily be decreased in post-traumatic events, significant inflammatory conditions and infections. Ingenbleek and Bernstein assert that prealbumin is at the ‘cutting edge of the equipoise’. ⁷

The normal reference interval for prealbumin in adults is 20–40 mg/dL (200–400 mg/L). Dellière and Cynobar proposed when C-reactive protein (CRP) exceeds 15 mg/L, prealbumin is not clinically interpretable. ⁹ Below this cut-off point of CRP, a prealbumin concentration of less than 20 mg/dL (200 mg/L)(or <15 mg/dL (150 mg/L) in the elderly) is thought to indicate malnutrition and less than 10 mg/dL (100 mg/L) severe malnutrition. ⁹ This prospective study included 216 inpatients, who were grouped into four categories based on CRP concentrations (<15 mg/L vs. ≥15 mg/L) and prealbumin (≥20 mg/dL [≥200 mg/L] vs. <20 mg/dL [<200 mg/L]). ¹⁰ It showed that the prevalence of malnutrition in CRP <15 mg/L with two prealbumin categories (14% vs. 49%) was significantly different, suggesting the usefulness of this prealbumin concentration. ¹⁰ Other factors which are known to influence prealbumin concentrations are age, gender and certain disease states. Prealbumin synthesis is decreased in starvation, liver diseases, dialysis, hyperthyroidism, hyperglycaemia, nephrotic syndrome, protein-losing enteropathy and acute blood loss.^9,11 Synthesis of prealbumin is increased by corticosteroids, NSAIDS, oral contraceptives and also in chronic renal failure and renal tubular damage due to reduced catabolism of prealbumin. The concentration of this protein tends to fluctuate with hydration status of the body.^9,11

Even though some studies in the literature propose prealbumin as a marker of nutritional status, others do not favour its significance in diagnosing or monitoring malnutrition. A study carried out on 102 children (51 malnourished and 51 well-nourished) in 1988 revealed that prealbumin is a sensitive and reliable marker to diagnose acute malnutrition when used along with anthropometric measurements. ¹² Prealbumin is also recommended as nutritional status indicator in several early studies, in various chronic disease conditions such as uncontrolled diabetes mellitus, ¹³ Reye syndrome, ¹⁴ cystic fibrosis ¹⁵ and anorexia nervosa. ¹⁶ It was also found to be useful in monitoring protein-energy status in the metabolic conditions like inborn errors of metabolism ¹⁷ and urea cycle defects. ¹⁸ Because of reprioritization of hepatic protein synthesis, the degree of visceral protein reduction has a solid inverse relationship with positive acute phase proteins such as CRP and orosomucoid (alpha-1-acid glycoprotein) in acute inflammatory conditions. This in turn correlates well with the clinical prognosis of the disease condition as well as the nutritional status of the patient. ¹⁹ Some investigators strongly believed that both prognostic value and the predicting value of the nutritional status of prealbumin are interrelated in an acute condition. ¹⁹ Based on this, the Prognostic Inflammatory and Nutritional Index (PINI) has been developed combining the two most reliable acute-phase reactants (CRP and orosomucoid) and laboratory nutritional markers (albumin and prealbumin) to assess and monitor prognosis of most pathological conditions. ¹⁹

Prealbumin has been shown to increase by 1 mg/day on meeting the nutritional requirements. ²⁰ Hence, some studies report that it is a sensitive biochemical marker to assess recent refeeding. Dellière and Cynobar described prealbumin as an ‘unrivalled marker for refeeding follow-up’. ⁹ The use of prealbumin for investigating the short-term effects of nutrition was first proposed in the 1970s. Pioneering work by Ingenbleek et al. showed that plasma concentrations of prealbumin were low in PEM children with Kwashiorkor and rapidly increased after correction. ²¹ In a series of small studies in Belgium carried out on non-injured patients, prealbumin was noted to rise earlier (within days) than albumin, transferrin and retinol-binding protein, following nutrition suppplement. ²² Similarly, two studies carried out in hospital patients with unknown ²³ or wide range of diagnoses ²⁴ and receiving only parenteral nutrition showed a rapid and significant elevation of prealbumin concentrations towards normal following a marked initial depletion.^23,24 This increase was not observed with other visceral proteins measured including albumin, transferrin and retinol-binding proteins.^23,24 In this study, although the baseline CRP was high, ROC curve analysis showed that patients with less than 104 mg/L of CRP had improved prealbumin concentrations. ²⁴ Equivalent results were obtained in a large cohort study based on 1056 critically ill trauma patients, who were divided into three groups according to calorie intake through the enteral route. ²⁵ Serial measurements of prealbumin concentrations suggested the group with the highest calorie feed had the greatest change in prealbumin concentration between the first and the third week. The general pattern across all calorie groups was the same: of note, significant differences of prealbumin only began to emerge in the third week when CRP started to decline. ²⁵ Prealbumin was high in the high calorie group (17 kcal/kg/day) and was 14 mg/dL (140 mg/L) compared with 9.9 mg/dL (99 mg/L) in the lowest calorie group (2 kcal/kg/day). ²⁵ It would be interesting to discover in a longer follow-up trial, how long prealbumin takes to normalize. Prealbumin was linearly related to enteric intake, when CRP was less than 100 mg/L, but not so when CRP is equal or more than 100 mg/L. ²⁵ This study shows, again, that increased acute phase reactants, increased vascular permeability, plasma protein extravasation and also large volume resuscitations in the early stages of a critical injury lead to inaccuracy of protein measurements. ²⁵ A meaningful upward trend of prealbumin was only apparent after two weeks, when the patients were more clinically stable. ²⁵ Dellière and Cynobar proposed that an increase in prealbumin more than 4 mg/dL (40 mg/L) per week indicates appropriate nutritional support, both in intensive care and non-intensive care settings, given that there is not a marked inflammatory response. ⁹

On the other hand, some studies negate the concept of prealbumin as a marker of nutritional status or refeeding adequacy. A study was carried out in 108 hospitalized patients to determine the better tool for assessing malnutrition using prealbumin, subjective global assessment and PINI against Detailed Nutritional Assessment (DNA). ²⁶ They found that prealbumin was the measure with good concordance with DNA (concordance index 76.8%). ²⁶ Prealbumin demonstrated the best sensitivity of 83.1% and intermediate specificity of 76.7% against reference DNA among the other two measures. ²⁶ However, they could not establish a significant difference between prealbumin concentration and DNA for patients who reached and did not reach 80% of their calorie requirements. ²⁶ To compound matters, a systematic review based on 1052 anorexic outpatients in 20 studies showed that prealbumin was normal (>20 mg/dL [>200 mg/L]) in subjects with marked nutrient deprivation and was low only at the extremes of starvation, when the BMI was lower than 12 kg/m². ¹⁰ Another systematic review by Lee et al. mentioned that serum prealbumin concentration has no value as a nutritional indicator in otherwise healthy subjects who are chronically or acutely undernourished, as serum concentrations show no difference until the effects of starvation are apparent with other measures such as clinical history and physical examination. ²⁷ Yeh et al. argued against adjusting nutritional prescriptions upon measuring prealbumin and other protein biomarkers based on the study of measured serial prealbumin in surgical intensive care patients. ²⁸

In favour of that, prealbumin is neither used in routine clinical practice nor mentioned in American Society of Parenteral and Enteral Nutrition (ASPEN) or The European Society of Clinical Nutrition and Metabolism (ESPEN) guidelines on nutritional assessment. ²⁹ One of the main reasons is its sensitivity to inflammation. ²⁹ Prealbumin is only mentioned in the guidelines in four countries: UK, Italy, Poland and France, but even within these countries, different cut-off values and purposes are cited. Interestingly, in the UK, prealbumin is mentioned in the NICE guidelines policy, but not used in clinical practice. Many years of poor consensus has led to prealbumin being popular among researchers, especially as a biomarker of nutritional recovery, but somewhat ignored in the larger nutritional community.

Prealbumin as a prognostic marker

Reduction in prealbumin concentration during acute inflammatory, infectious or traumatic conditions is multifactorial. These include cytokine-induced down-regulation of synthesis, extravasation from the vascular system, haemodilution and possible increased consumption. Therefore, it has been suggested that reduced prealbumin concentration reflects the disease severity, hence its potential use as a prognostic indicator. PINI score is an accurate and consistent grading system developed to stratify critically ill patients rapidly and inexpensively by risk of complications or death. ¹⁹ Following its development, PINI has been evaluated along with its individual determinants at baseline and up to 28 days, in 15 critically ill trauma patients who received nutritionally complete enteral feeds. ³⁰ Prealbumin concentrations were significantly increased in patients discharged from critical care units than the deceased in a study carried out in 154 critical care patients. ³¹ Authors suggested that PEM in critically-ill patients is markedly different from simple starvation, and therefore early provision of nutritional therapy is pivotal in the prognosis. ³¹ Devakonda et al. identified prealbumin as a marker of stress-related hypermetabolism in critically ill patients. ³² Serum prealbumin remains low despite the initial nutritional support, as these patients do not reach anabolic status rapidly. ³³ Furthermore, they suggested that serum prealbumin concentration was correlated with length of stay in intensive care or hospital, Acute Physiology And Chronic Health Evaluation II (APACHE 11) score and mortality. ³³ In contrast, Sullivan et al. described that neither serum albumin nor prealbumin has a significant role in predicting outcome or nutritional status in controlled acute illnesses based on the prospective study carried out in elderly patients who were suffering from non-terminal illnesses. ³² The serum prealbumin concentration can drop to 50% as a response to a major physiologic stress to the body and it will take about three to five days to have a similar impact on prealbumin concentration in a healthy individual with very low nutrition. ³² Hence, a low prealbumin concentration in blood does not necessarily demonstrate the severity of the pathological condition or the extent of any potential nutritional deficit. ³²

Patients with acute kidney injury (AKI) with a serum prealbumin <11 mg/dL (<110 mg/L) (median) vs. serum prealbumin concentration  ≥ 11 mg/dL (≥110 mg/L) showed significant in-hospital mortality rate (45.0% vs. 19.8%, P = 0.01). ³⁴ This indicates that serum prealbumin concentrations <11 mg/dL (<110 mg/L) were a strong predictor of a high risk of mortality independent of AKI severity, comorbid illnesses, serum CRP concentrations and other possible confounders. ³⁴ Moreover, each 5 mg/dL (50 mg/L) increment of serum prealbumin concentration corresponded to an adjusted 29% decline of in-hospital mortality (hazard ratio 0.71; 95% confidence interval 0.52 to 0.96). ³⁴ Xie et al. suggested that CRP/prealbumin ratio remains an independent predictor of mortality of AKI patients, following the control of selected possible predictors for mortality of AKI patients such as age, gender, sepsis, sequential organ failure assessment (SOFA) score in multivariable analysis. ³⁵ When risk profiles for CRP/prealbumin ratio were prepared according to quartiles, the values above the 25th percentile were related with progressively higher risk of mortality after adjusting for age and gender. ³⁵ In addition, when using a median CRP/prealbumin ratio of 0.42 as cut-off, the mortality rate was dramatically higher in the CRP/prealbumin ratio of >0.42 group at the end of the follow-up period. ³⁵ Prealbumin alone has been investigated and found to be predictive of morbidity and mortality of diverse surgical and non-surgical patient categories such as haemodialysis, ³⁶ surgery for ovarian cancers, ²⁶ surgery for gastric conditions, ³⁷ cardiac surgeries, ³⁸ post-pneumonectomy complications, ³⁹ burn patients ⁴⁰ and strokes.^41,42

On the contrary, Lim et al. reported that serum prealbumin is not sensitive in assessing the prognosis of critically ill patients based on their study of 44 patients who received parenteral nutrition supplements for more than seven days. ⁴³ Rasheed and Woods appreciated the same, suggesting that prealbumin concentration was less significant as an independent marker in terms of predicting the quality of life in older hospitalized patients for non-terminal illnesses. ⁴⁴ Prealbumin and CRP/prealbumin ratio have been assessed as a prognostic score along with albumin, CRP and CRP/albumin ratio in patients receiving parenteral nutrition in a four-year retrospective study. ⁴⁴ Both CRP/prealbumin and CRP/albumin were found to be strong predictors of parenteral nutrition duration, the length of intensive care stay and the duration of mechanical ventilation in both univariate Kaplan-Meier survival analysis and multivariate COX survival analysis. ⁴⁵ Although both indicators were significantly related to exitus, infection, sepsis and liver failure in the univariate approach, only the CRP/albumin ratio was predictive of the development of renal failure. ⁴⁵ As the final conclusion, they suggested that the CRP/albumin score has more predictive relationship with morbidity and mortality at the start of parenteral nutrition supplement, than CRP/prealbumin combination or CRP, albumin and prealbumin alone. ⁴⁵ Even though both high-sensitive CRP and prealbumin can theoretically be used as markers of disease prognosis and mortality, only high-sensitive CRP has proven to be effective in prognosticating the mortality in acutely ill geriatric patients. ⁴⁶

Prealbumin, analytical methodologies

The measurement of prealbumin concentration in blood is challenging, as it is small in size and quantity comparison to albumin. It was first separated from other proteins using an electrophoretic technique in a concentrated cerebral spinal fluid sample in 1942. ⁴⁷ Since then, different techniques have been attempted to identify and quantify prealbumin such as electrophoretic methods, radio-isotopic methods, a spectrum of immunoassay techniques, light scattering methods and mass spectrometry (MS). In 2002, De Nayar categorized the development of analytical methods used to measure prealbumin into three key stages depending on a chronological and functional approach. ⁴⁸ In the first phase, prealbumin was identified based on classical protein chemistry methods, in the second phase prealbumin was demonstrated as the thyroid hormone-binding protein using radio-isotopic techniques and in the third phase prealbumin was established as a nutritional marker with field studies on nutrition. ⁴⁸ At that stage, structural studies and mutation analysis of prealbumin, which aided in the diagnosis of amyloid neuropathy was only available in research settings. ⁴⁸

The study of circulating prealbumin was initiated with electrophoretic techniques using different migrating media such as paper sheet, starch gel and polyacrylamide gel and various buffering systems such as in reverse-flow electrophoresis. ⁴⁷ Prealbumin was identified with its faster migration towards the anode than albumin in the media with pH ∼8.6. ² Later, this technique has been modified to immune-electrophoresis following isolation of purified prealbumin from human plasma. ⁴⁷ With the advancement of specific antibody preparations against the purified prealbumin, a wide spectrum of immunological methods has been adopted to measure this protein with improved sensitivity and specificity. ⁴⁷ These methods were ranging from simple and older radial immunodiffusion (RID), electro-immunoassay method to immune-fluorescence, immune-turbidimetry, immune-nephelometry and comparatively more complex enzyme-linked immunosorbent assay (ELISA). ⁴⁷ Among them, immune-diffusion and electro-immunoassays are time-consuming and in general RID methods require a 24–48 h incubation period to observe complete antigen–antibody precipitin formation. ⁴⁷ Lee C et al. compared competitive enzyme immunoassay (EIA) with conventional RID method, in which EIA method demonstrated accurate and reproducible results with a 1 h turnaround time. ⁴⁹ The measurement range of this method was 1–35 mg/dL (10–350 mg/L). ⁴⁹ Both methods were well correlated (y= 1.03x + 5.92, r = 0.93), even though the EIA method demonstrated good specificity with no significant interference from haemolysis, icterus and lipaemia. ⁴⁹ Moreover, it was suggested to be well adapted for routine laboratory use with automated platforms and commercially available reagents. McCarthy et al. compared three immunoassay methods including immune-turbidimetric assay (Cobas Bio centrifugal analyser), a rate nephelometry assay (Beckman Instruments) and a radial immunodiffusion assay (Behring Diagnostics) for precision, linearity and correlation in measuring prealbumin in a paediatric population. ⁵⁰ Both light-scattering methods demonstrated similar within-run and between-run imprecision, whereas radial immunodiffusion assay demonstrated higher between-run imprecision. ⁵¹ However, all three assays correlated well in measuring prealbumin. ⁵⁰ Holownia et al. proposed that the sensitivity of the light-scattering assay can be improved significantly by using particle-enhanced techniques in comparison to the conventional non-enhanced methods. ⁵¹ They have developed and evaluated a latex-particle-enhanced immune-turbidimetric assay in an automated platform (Dimension Clinical Chemistry analyser) with good precision and specificity. ⁵¹ Purified prealbumin (>96% purity) has been used as the calibration material (Scipac, Kent, UK; product code P171-1). ¹⁰ This newly developed method has been compared for prealbumin using both serum and heparin or EDTA anticoagulated plasma, with the selected reference method (Beckman Array system, Beckman Instruments) which has been calibrated against the International Federation of Clinical Chemistry (IFCC) reference material CRM 470. ⁵¹ The authors observed that the prealbumin concentrations were independent of sample type and also no interference from haemolysis (haemoglobin up to 77 g/dL), lipaemia (triglycerides up to 12.5 mmol/L) and icterus (bilirubin up to 550 µmol/L). ⁵¹ Furthermore, there was no notable cross-reaction between albumin and prealbumin in latex-enhanced particle immunoassay. ⁵¹ The analytical measurement range of the assay was improved to 0.8–50 mg/dL (8–500 mg/L). ⁵¹ Prealbumin in cerebrospinal fluids, which is in nanogram amounts, was quantified using a sensitive ELISA assay in 1991 along with serum prealbumin. ⁵² The assay demonstrated 5.1 and 6.1% within-run and between-run CV%, respectively, in measuring the protein in both fluid types. ⁵² In addition, the authors reported a significant correlation between CSF and corresponding serum prealbumin concentrations. ⁵² A point-of-care testing device (POCT) was developed using an immuno-chromatography method to measure prealbumin in 10 µL of whole blood or serum in 2014. ⁵³ A good correlation of prealbumin concentrations between the POCT device and the nephelometry (y = 0.927x +2.62, r = 0.935, n = 64) was demonstrated, and the linearity was 8.7–35.4 mg/dL (87–354 mg/L). ⁵³ No interference was demonstrated from haemolysis, lipaemia, icterus or rheumatoid factor. ⁵³ However, if haematocrit increases from 1% in the sample, the measured prealbumin concentration decreases by 1%. ⁵³ Because this device exhibited good performance characteristics, it was suggested as a useful test for bedside nutritional monitoring.

Although various immunochemical techniques were developed and validated to assay prealbumin, the most popular methods in clinical laboratory at present are automated light-scattering methods including both immune-nephelometry and immune-turbidimetry. ² Good specificity and sensitivity and short turnaround time make these methods popular in quantifying prealbumin. Nephelometry is considered as the reference method for serum protein determination. However, turbidimetry is the preference for most of the clinical laboratories, as it could be integrated in to the routine automated clinical biochemistry analyser, whereas nephelometry requires a specific instrument. The measurements are affected by the common drawback of light-scattering methods including interference from gross lipaemia and haemolysis. A study evaluated 140 serum samples from 15 hospitals across France to compare prealbumin measured by both these methods. ⁵⁴ Prealbumin concentration was determined using two automated nephelometries and five automated biochemistry analysers with turbidimetry. ⁵⁴ The authors concluded that there was no difference between the prealbumin values obtained from both methods, but they suggested that the choice of antibodies and standardization procedures may affect the transferability of the results. ⁵⁴

Preanalytical factors that can affect prealbumin concentration are similar to that which affects total protein concentration. In particular, the position of the body, such as a long period of standing or recumbent position before drawing blood will result in higher or lower values, respectively. The standard reference concentration for prealbumin was assigned in CRM 470, which is the international reference material for serum protein.^55,56 The reference value has been assigned by an accurate and precise value transfer method using highly purified and highly characterized prealbumin.^55,56 However, there can be a degree of uncertainty in the prealbumin values obtained by different methods due to relatively low concentrations in the blood and differences in antiserum specificity and reactivity.

In addition to quantifying prealbumin, now it is possible to detect different proteoforms of prealbumin that help in diagnosing amyloidosis. Highly sensitive analytical techniques are used for this purpose. The structure of the prealbumin has been determined by MS using either bottom-up or top-down approaches. Proteolytic digestion of prealbumin is used in the bottom-up method which in turn is readily analysed by liquid chromatography mass spectrometry (LC-MS), but carries disadvantages such as labour intensive, time consuming in sample preparation with less than 100% sequence coverage. ⁵⁷ Conversely, in the top-down approach, the samples were directly introduced into the MS without a proteolytic digestion step. Hence, the complete structural information of proteoforms can be obtained. ⁵⁷ The latter approach is more efficient due to fewer steps involved. ⁵⁷ Trenchevska et al. introduced a step-forward high throughput, rapid and convenient MS immunoassay technique in identifying and quantifying prealbumin isoforms. ⁵⁸ This was a two-step approach; initially, immuno-affinity separation of proteoforms with polyclonal antibodies that recognize most of the variants. Subsequently, the different variants, especially those results from point mutations, were detected by MS. ⁵⁸ Further identification of the prealbumin variants was performed using on-the spot trypsin and endoproteinase Arg-C digestion. ⁵⁸ On-the spot enzyme digestion reduced the time to several minutes which is facilitated by localization of the protein sample on the flat matrix-assisted laser desorption/ionization target surface and high trypsin concentration acting on that. ⁵⁸ Later, Pont et al. compared capillary electrophoresis and capillary LC-MS associated with a novel sample pretreatment method based on immunoprecipitation. ⁵⁹ Apparently, immunoprecipitation provides a higher grade of selectivity. However, these techniques detect similar proteoforms with same relative quantifications. Furthermore, both these methods have inherent similar reproducibility and migration/retention times, although only minor differences have been reported such as slightly reduced lower limit of detection in capillary LC-MS. ⁵⁹ A well-advanced novel method of purification has been attempted using immune-affinity solid-phase extraction capillary electrophoresis mass spectrometry (IA-SPE-CE-MS) to separate prealbumin in serum from familial amyloidosis polyneuropathy type 1 patients and healthy subjects. ⁶⁰ Immuno-affinity extraction was investigated both online and offline using three different magnetic beads prepared with specific polyclonal antibodies, preceded by a simple offline sample pretreatment with 5% (v/v) phenol for precipitation of the most abundant protein. ⁶⁰ The authors demonstrated that the microcartridge lifetime (>20 analyses/day) and repeatability were good with the IA-SPE-CE-MS, provided optimum pH, temperature and ionic strength are maintained. Hence, this was suggested as a potential method to screen familial amyloidosis polyneuropathy type-1 patients. ⁶⁰

Conclusion

The notion that prealbumin can be used as a nutritional marker remains controversial. However, evidence suggests that it can complement other parameters such as clinical history, anthropometric assessment and physical examination in assessing undernutrition. Importantly, current analytical methodologies are well advanced in providing rapid and accurate prealbumin results and identifying its proteoforms. However, further international consensus is required on the threshold value to diagnose malnutrition and establish prealbumin as a marker of nutritional status in clinical practice.