Albumin is an important binding and transport protein for various substances in plasma and the main contributor to the plasma osmotic pressure. Measurement of albumin in serum is used for diagnosis and monitoring of liver diseases, e.g. liver cirrhosis. Furthermore, albumin levels indicate the health and nutritional status of an individual and, therefore, are used for detecting malnutrition and for prognosis in elderly hospitalized patients.

Alanine Aminotransferase (ALAT/ALT), formerly called Glutamic Pyruvic Transaminase (GPT) and Aspartate Aminotransferase (ASAT/AST), formerly called Glutamic Oxalacetic Transaminase (GOT) are the most important representatives of a group of enzymes, the aminotransferases or transaminases, which catalyze the conversion of α-keto acids into amino acids by transfer of amino groups. As a liver-specific enzyme, ALAT is only significantly elevated in hepatobiliary diseases. Increased ASAT levels, however, can occur in connection with damages of heart or skeletal muscle as well as of liver parenchyma. Parallel measurement of ALAT and ASAT is, therefore, applied to distinguish liver from heart or skeletal muscle damages. The ASAT/ALAT ratio is used for differential diagnosis in liver diseases. While ratios 1 indicate mild liver damage, ratios > 1 are associated with severe, often chronic liver diseases.

Alkaline Phosphatase (AP), a hydrolytic enzyme acting optimally at alkaline pH, exists in blood in numerous distinct forms which originate mainly from bone and liver, but also from other tissues as kidney, placenta, testes, thymus, lung, and tumors. Physiological increases are found during bone growth in childhood and in pregnancy, while pathological increases are largely associated with hepatobiliary and bone diseases. In hepatobiliary diseases, they indicate obstruction of the bile ducts as in cholestasis caused by gall stones, tumors, or inflammation. Elevated activities are also observed in infectious hepatitis. In bone diseases, elevated AP activities originate from increased osteoblastic activity as in Paget’s disease, osteomalacia (rickets), bone metastases, and hyperparathyroidism.

Alanine Aminotransferase (ALAT/ALT), formerly called Glutamic Pyruvic Transaminase (GPT), and Aspartate Aminotransferase (ASAT/AST), formerly called Glutamic Oxalacetic Transaminase (GOT), are the most important representatives of a group of enzymes, the amino-transferases or transaminases, which catalyze the conversion of a-keto acids into amino acids by transfer of amino groups. As a liver-specific enzyme, ALAT is only significantly elevated in hepatobiliary diseases. Increased ASAT levels, however, can occur in connection with damages of heart or skeletal muscle as well as of liver parenchyma. Parallel measurement of ALAT and ASAT is, therefore, applied to distinguish liver from heart or skeletal muscle damages. The ASAT/ALAT ratio is used for differential diagnosis in liver diseases. While ratios 1 indicate mild liver damage, ratios > 1 are associated with severe, often chronic liver diseases.

Bilirubin is a breakdown product of hemoglobin. Free, unconjugated bilirubin is extremely apolar and nearly insoluble in water, thus forming a complex with albumin for the transport in the blood from the spleen to the liver. In the liver, bilirubin is conjugated with glucuronic acid, and the resulting water-soluble bilirubin glucuronic acid is excreted via the bile ducts.

Hyperbilirubinemia can be caused by increased bilirubin production due to hemolysis (pre-hepatic jaundice), parenchymal damages of the liver (intra-hepatic jaundice) or by occlusion of bile ducts (post-hepatic jaundice). A chronic congenital (predominantly unconjugated) hyperbilirubinemia called Gilbert’s syndrome is quite frequent in the population. High levels of total bilirubin are observed in 60 - 70 % of neonates due to an increased postpartum breakdown of erythrocytes and because of the delayed function of enzymes for bilirubin degradation. Common bilirubin methods detect either total bilirubin or direct bilirubin. Determinations of direct bilirubin measure mainly conjugated, water-soluble bilirubin. Unconjugated bilirubin can therefore be estimated as the difference between total bilirubin and direct bilirubin.

Bilirubin is a breakdown product of hemoglobin. Free, unconjugated bilirubin is extremely apolar and nearly insoluble in water, thus forming a complex with albumin for the transport in the blood from the spleen to the liver. In the liver, bilirubin is conjugated with glucuronic acid, and the resulting water-soluble bilirubin glucuronic acid is excreted via the bile ducts.

Hyperbilirubinemia can be caused by increased bilirubin production due to hemolysis (pre-hepatic jaundice), parenchymal damages of the liver (intra-hepatic jaundice) or by occlusion of bile ducts (post-hepatic jaundice). A chronic congenital (predominantly unconjugated) hyperbilirubinemia called Gilbert’s syndrome is quite frequent in the population. High levels of total bilirubin are observed in 60 - 70 % of neonates due to an increased postpartum breakdown of erythrocytes and because of the delayed function of enzymes for bilirubin degradation. Common bilirubin methods detect either total bilirubin or direct bilirubin. Determinations of direct bilirubin measure mainly conjugated, water-soluble bilirubin. Unconjugated bilirubin can therefore be estimated as the difference between total bilirubin and direct bilirubin.

Calcium plays an essential role in many cell functions: intracellular in muscle contraction and glycogen metabolism, extracellular in bone mineralization, in blood coagulation and in transmission of nerve impulses. Calcium in plasma exists in three forms: free, bound to proteins or bound to anions such as phosphate, citrate and bicarbonate in a complex reaction. Decreased total calcium levels can be associated with diseases of the bone apparatus (especially osteoporosis), kidney diseases (especially under dialysis), defective intestinal absorption and hypoparathyroidism. Increased total calcium can be measured in hyperparathyroidism, malignant diseases with metastases and sarcoidosis. Calcium measurements also help in monitoring of calcium supplementation mainly in the prevention of osteoporosis.

Cholesterol is a component off cell membranes and a precursor for steroid hormones and bile acids synthesized by body cells and absorbed with food. Cholesterol is transported in plasma via lipoproteins, namely complexes between lipids and apolipoproteins. There are four classes of lipoproteins: high-density lipoproteins (HDL), low-density lipoproteins (LDL), very-low-density lipoproteins (VLDL), and chylomicrons. While LDL is involved in cholesterol transport to the peripheral cells, HDL is responsible for the cholesterol uptake from the cells. The four different lipoprotein classes show a distinct relationship to coronary atherosclerosis. LDL-cholesterol (LDL-C) contributes to atherosclerotic plaque formation within the arterial intima and is strongly associated with coronary heart disease (CHD) and related mortality. Even with total cholesterol within the normal range, an increased concentration of LDL-C indicates high risk. HDL-C has a protective effect impeding plaque formation and shows an inverse relationship to CHD prevalence. In fact, low HDL-C values constitute an independent risk factor. The determination of the individual total cholesterol (TC) level is used for screening purposes while for a better risk assessment it is necessary to measure additionally HDL-C and LDL-C. In the last few years, several controlled clinical trials using diet, lifestyle changes and/or different drugs (especially HMG CoA reductase inhibitors [statins]) have demonstrated that lowering total cholesterol and LDL-C levels reduce drastically CHD risk.

Cholinesterase (ChE) is a group of enzymes that are broken down into choline and thiocholine esters. The names Serum Cholinesterase and Pseucholinesterase are also commonly used. ChE measurements in serum and plasma are synthesized in the liver and are prescribed in the diagnosis of liver disease, nephrotic syndrome and intestinal diseases with protein loss (exudative enterudate). Very low values ​​may indicate pesticide poisoning. ChE measurement is also part of preoperative diagnostics because ChE is required for the inactivation of muscle relaxants that are often used during surgery.

Creatine kinase (CK) is an enzyme consisting of isoenzymes mainly in muscle (CK-M) and brain (CK-B). CK is found in the human body in dimeric form as CK-MM, CK-MB, CK-BB as a macro-enzyme. The CK-MB measurement is a specialized test for detecting cardiac muscle damage and, therefore, is used for the diagnosis and monitoring of myocardial infarction.

Creatinine is a waste product excreted by the kidneys mainly by glomerular filtration. The concentration of creatinine in the plasma of a healthy individual is fairly constant, independent of water intake, exercise, and rate of urine production. Therefore, increased plasma creatinine values always indicate decreased excretion, i.e. impaired kidney function. The creatinine clearance enables a quite good estimation of the glomerular filtration rate (GFR) which allows better detection of kidney diseases and monitoring of renal function. For this purpose, creatinine is measured simultaneously in serum and urine collected over a defined time period.

Creatinine is a waste product excreted by the kidneys mainly by glomerular filtration. The concentration of creatinine in the plasma of a healthy individual is fairly constant, independent of water intake, exercise, and rate of urine production. Therefore, increased plasma creatinine values always indicate decreased excretion, i.e. impaired kidney function. The creatinine clearance enables a quite good estimation of the glomerular filtration rate (GFR) which allows better detection of kidney diseases and monitoring of renal function. For this purpose, creatinine is measured simultaneously in serum and urine collected over a defined time period.

Gamma-glutamyltransferase (gamma-GT/GGT), also called gamma-glutamyl transpeptidase, is an enzyme present in the liver and bile ducts and is the most sensitive indicator of hepatobiliary disease. Due to the high negative predictive value for these diseases, gamma-GT measurements are widely used to exclude the presence of diseases of liver or biliary origin. Together with other enzymes such as alanine aminotransferase (ALAT), aspartate aminotransferase (ASAT), and cholinesterase, gamma-GT is a potential marker for the differential diagnosis of liver disease.

Measurement of glucose concentration in serum or plasma is mainly used in the diagnosis and monitoring of the therapy of diabetes mellitus. Other applications are for the detection of neonatal hypoglycemia, pancreatic islet cell carcinoma, and the evaluation of carbohydrate metabolism in various diseases.

Pengukuran konsentrasi glukosa dalam serum atau plasma terutama digunakan dalam diagnosis dan pemantauan terapi diabetes mellitus. Aplikasi lain adalah untuk deteksi hipoglikemia pada neonatal, karsinoma sel islet pankreas serta evaluasi metabolisme karbohidrat pada berbagai penyakit.

Zat besi ada dalam tubuh sebagai komponen hemoglobin dan mioglobin serta terikat untuk transferin untuk transportasi dalam plasma dan disimpan dalam feritin. Peningkatan konsentrasi zat besi terjadi pada hemokromatosis dan kerusakan hati. Malabsorpsi merupakan penyakit pencernaan yang dapat menyebabkan penurunan kadar zat besi, dan dengan demikian dapat menyebabkan anemia. Kehilangan darah setelah lesi gastrointestinal atau perdarahan menstruasi yang berat dapat menyebabkan anemia juga.

Substrat lipase diproduksi secara sintetis (1,2-o-dilauryl-rac- glycero-3-glutaric acid- (6-methylresorufin) ester) dalam mikro- emulsi yang secara khusus dipecah oleh lipase dikarenakan adanya kolipase dan asam empedu. Perpaduan antara lipase dan asam empedu membuat uji ini spesifik dan terpercaya untuk lipase pada pankreas tanpa reaksi lainnya dikarenakan enzim lipolitik atau esterase. Komposisi reagen telah dioptimalkan secara menyeluruh sehingga tidak ada efek matriks serum. Metilresorufin-ester yang dihasilkan secara spontan terdegradasi menjadi metilresorufin. Absorbansi oleh pewarna merah ini berbanding lurus dengan aktivitas lipase dalam sampel.

Kekurangan magnesium merupakan gangguan yang cukup umum terjadi, disebabkan oleh kekurangan gizi, malabsorpsi, kehilangan ginjal dan gangguan endokrin. Komplikasi yang berhubungan dengan penurunan konsentrasi magnesium yang iritabilitas neuromuskular (misalnya tremor, kejang) dan gejala jantung (misalnya takikardia, aritmia). Penurunan konsentrasi magnesium sering terkait dengan penurunan tingkat kalsium dan kalium, hypomagnesemia mungkin merupakan penyebab utama hipokalsemia. Peningkatan nilai magnesium dapat diamati saat dehidrasi, gangguan ginjal dan setelah mengkonsumsi antasida secara berlebih dan dapat dikaitkan dengan melemahnya refleks dan rendahnya tekanan darah.  

Amilase pankreas adalah enzim yang diproduksi oleh jaringan eksokrin pankreas untuk membantu proses pencernaan pati. Enzim ini bertanggung jawab dalam mencerna banyak jenis gula yang kemudian akan dilepaskan ke aliran darah ketika pankreas meradang. Uji amilase pankreas adalah tes diagnostik in vitro untuk penentuan kuantitatif amilase pankreas dalam serum dan plasma dengan kolorimetri enzimatik.

Fosfor terdapat di dalam tubuh sebagai fosfat, terutama sebagai bahan anorganik untuk tulang, serta di dalam sel fosfolipid dan asam nukleat serta adenosin trifosfat, yang terlibat dalam transfer energi. Dalam plasma hadir sebagai kalsium fosfat; oleh karena itu, tingkat plasma fosfor sangat terkait dengan tingkat kalsium. Pengukuran fosfor dalam serum dan urin terutama dilakukan untuk mendeteksi gangguan ginjal, tulang dan paratiroid kelenjar. Peningkatan konsentrasi ditemukan pada gagal ginjal, hypoparathyroidism, pseudo-hyperparathyroidism dan hilangnya kalsium fosfat tulang dan sel. Penurunan nilai terjadi di malabsorpsi, hiperparatiroidisme dan defisiensi vitamin D. Informasi tambahan dapat diperoleh dengan tambahan pengukuran kalsium.

Pengukuran protein total berguna dalam mengidentifikasi berbagai gangguan pada tubuh. Penurunan konsentrasi protein total dapat terdeteksi pada penurunan sintesis protein dari hati, kehilangan protein karena fungsi ginjal terganggu, malabsorpsi atau defisiensi gizi. Peningkatan kadar protein juga terjadi pada gangguan inflamasi kronis, sirosis hati dan dehidrasi.

Trigliserida adalah ester dari gliserol dengan tiga asam lemak dan merupakan lemak alami yang paling banyak jumlahnya. Dalam plasma, trigliserida berikatan dengan apolipoprotein membentuk lipoprotein densitas sangat rendah (VLDL) dan kilomikron. Pengukuran trigliserida digunakan dalam skrining status lemak untuk mendeteksi risiko aterosklerotik dan memantau terapi obat penurun lemak. Berbagai penelitian menunjukkan bahwa peningkatan konsentrasi trigliserida bersamaan dengan peningkatan lipoprotein densitas rendah (LDL) merupakan risiko tinggi untuk penyakit jantung koroner (PJK). Kadar trigliserida yang tinggi juga terjadi pada berbagai penyakit hati, ginjal dan pankreas.

Pengukuran unsaturated iron binding capacity (UIBC) yang dikombinasikan dengan serum besi merupakan alat diagnostik yang berguna untuk penentuan berbagai macam gangguan zat besi dalam tubuh. Jumlah UIBC dan serum besi memberikan nilai total iron binding capacity (TIBC). TIBC mewakili konsentrasi maksimal zat besi yang dapat diikat oleh serum protein. Kadar UIBC dalam serum bervariasi tergantung pada gangguan metabolisme, dimana kapasitas zat besi sering meningkat pada kasus defisiensi zat besi dan menurun pada gangguan inflamasi kronis atau penyakit berbahaya.

Urea adalah produk katabolisme protein yang mengandung nitrogen. Peningkatan kadar urea yang tinggi dalam darah yang disebut sebagai hiperuremia atau azotemia. Penentuan paralel urea dan kreatinin dilakukan untuk membedakan azotemia antara pra-ginjal dan pasca- ginjal. Azotemia pra-ginjal, disebabkan oleh dehidrasi, peningkatan katabolisme protein, pengobatan dengan kortisol atau penurunan perfusi ginjal, menyebabkan peningkatan kadar urea, sementara kadar kreatinin tetap dalam rentang rujukan. Dalam azotemia pasca-ginjal, disebabkan oleh sumbatan pada saluran kemih, baik kadar urea maupun kreatinin meningkat, tetapi peningkatan kreatinin dalam batas yang lebih kecil. Pada penyakit ginjal, konsentrasi urea tinggi ketika laju filtrasi glomerulus berkurang dan asupan protein lebih tinggi dari 200 g/hari.

Asam urat dan garamnya adalah produk akhir dari metabolisme purin. Pada penyakit gout, komplikasi dari hiperurisemia (peningkatan kadar asam urat) mengarah pada pembentukan kristal monosodium urat di sekitar sendi-sendi. Penyebab lain kadar asam urat yang tinggi dalam darah adalah adanya penyakit ginjal yang menyebabkan penurunan ekskresi sisa metabolisme, kelaparan, penyalahgunaan obat dan konsumsi alkohol yang meningkat serta penggunaan obat-obat tertentu. Asam urat yang tinggi juga dapat menjadi faktor risiko untuk penyakit jantung koroner secara tidak langsung. Hipourisemia jarang terjadi dan pada umumnya terkait dengan gangguan metabolik keturunan.