Discriminant functions in differential diagnosis of hypercalcaemia

Filtering clinically significant hypercalcaemia from non-significant hypercalcaemia at the laboratory level

In an earlier study it was shown, that, in a hospital population, only about 30% of patients with hypercalcaemia had the diagnosis identified and so an alarm filter was developed, at the laboratory level, to differentiate between clinically significant and clinically non-significant hypercalcaemia. The filter correctly classified 84% and 77% of women and men with hypercalcaemia, respectively, with respect to the clinical significance of the hypercalcaemia. The sensitivity and the specificity of the discriminant functions were 90% and 73% in women and 80% and 67% in men. The alarm filter was based on a two-step procedure. The patients were primarily classified by the discriminant functions into one of the following medical diagnoses related to hypercalcaemia: primary hyperparathyroidism, malignancy, and transient hypercalcaemia. Based on this classification the patients were characterized as having either a clinically significant or non-significant hypercalcaemia. The alarm filter was based on two discriminant functions. The discriminant variables were phosphate, albumin, protein, LD, and a haemoglobin in women, and albumin, protein, ALP, and age in men. Missing values were estimated. The discriminant variables were selected from 17 possible discriminant variables, all measured by routine, and age. The study group comprised 257 patients with hypercalcaemia, consecutively registered, during half a year. The classification efficiency of the discriminant functions were based on comparison of results obtained by cross-validation of the discriminant functions, and the medical diagnosis decided by the clinicians in the respective departments of the hospital. The medical diagnoses were based on principles and definitions generally used in the departments with no knowledge of the results assessed by the discriminant functions.

Differential diagnosis of hypercalcemia

The differential diagnosis of hypercalcemia has expanded to over 25 separate disease states, with primary hyperparathyroidism and malignancy accounting for 80-90% of all hypercalcemic patients. Primary hyperparathyroidism comprises the majority of hypercalcemic patients among the ambulatory population, but malignancy accounts for up to 65% of such patients in the hospital. Factors favoring primary hyperparathyroidism include a family history of hyperparathyroidism or multiple endocrine neoplasia, a history of childhood radiation to the head and neck, the postmenopausal state, a history of renal calculi or peptic ulcer, hypertension, the induction of hypercalcemia by thiazides, or an asymptomatic patient with a prolonged, stable mild hypercalcemia. The usefulness of the serum calcium, parathyroid hormone, chloride, phosphorus, serum 25-OHD, and 1,25-(OH)2D, and urinary calcium in the differential diagnosis of hypercalcemia is discussed. The pitfalls of an excessive reliance on the serum PTH in diagnosing hyperparathyroidism are stressed. The discriminant values of the serum calcium, chloride, phosphorus, and parathyroid hormone are explored, with the serum parathyroid hormone, chloride, and calcium proving most useful in separating primary hyperparathyroidism from other forms of hypercalcemia. Multivariate discriminant analysis using the serum calcium, phosphorus, and chloride and the hematocrit achieves an accuracy of 95-98% and is the most economical method of identifying hyperparathyroidism. The addition of the amino-terminal or intact PTH assay increases the accuracy to 99% and is essential in the presence of renal insufficiency.

Hypercalcaemia and the synthesis of interleukin-1 by an ameloblastoma

A case of hypercalcaemia secondary to a long-standing solitary ameloblastoma is presented with evidence to suggest that the raised plasma calcium was the result of the secretion of interleukin-1 and a parathyroid hormone-like substances by the tumour. The aetiology of humoral hypercalcaemia of malignancy is discussed in relation to the role played by these substances.

On the sensitivity of linear discriminant analysis to sampling variation and analytical errors

The influence of analytical inaccuracy and imprecision on the linear discriminant function is considered. Analytical shifts occurring between the analysis of samples from each of two groups give spuriously low error rates if the function is evaluated on the training set, notably at high dimensions. Inaccuracy arising after the establishment of a discriminant function may change considerably the individual group error rates whereas the overall error rate is moderately affected. Imprecision decreases the group separation by an amount comparable to that in the univariate situation. In conclusion, evaluation of the error rates of a discriminant function on an independent test set is important to obtain realistic estimates of the performance and is preferable to using unbiased statistical methods or the split-sample principle based solely upon the training set.

Value of laboratory tests in the differential diagnosis of hypercalcemia

Eighteen laboratory tests were compared in the differentiation of primary hyperparathyroidism from hypercalcemia associated with malignancy. Statistical comparisons of the test results were carried out in four patient groups and two control groups. The patient groups evaluated were those with confirmed primary hyperparathyroidism, those with malignancy with hypercalcemia, those with malignancy without hypercalcemia, and those with surgically cured primary hyperparathyroidism. These groups allowed determination of the relative diagnostic values of the tests and a rationale for their value. After exclusion of patients with renal failure from the patient and control groups, these data indicated that the laboratory tests with the greatest differential diagnostic value, in order of efficacy, were: albumin, carboxy-terminal parathyroid hormone, venous pH, cholesterol, chloride, alkaline phosphatase, phosphorus, and the chloride/phosphate ratio. Hemoglobin, hematocrit, and red blood cell count also had some value, particularly in male patients. However, none of these tests individually achieved better than an 81 percent classification accuracy. With application of logistic discriminant analysis, only three tests--albumin, parathyroid hormone, and chloride--were identified as statistically significant in jointly improving the diagnostic separation between these two patient groups. Although the 94.4 percent classification accuracy achieved by use of these three variables in a logistic discriminant function was better than that obtained with any individual variable, incorrect classification was still a significant problem, particularly in the case of patients with malignancy and high concentrations of parathyroid hormone. With the exception of albumin and chloride measurements, the commonly available ancillary laboratory tests proposed to aid this differential diagnosis do not give any more information than the analysis of parathyroid hormone alone and merely add to the increased cost of medical care.

Predicting the outcome of acute stroke: a prognostic score

A prognostic score was derived from a prospective study of 148 consecutively admitted patients, aged less than 76 years, who survived the first 24 hours after an acute stroke. Multivariate analysis was used to compare the presenting clinical features of 137 (93%) of these patients with their outcome after two months. Little change in the level of residual disability was detected in 128 of these patients after a further four months. The features which were found to predict functional dependence or death included older age, complete limb paralysis, depression of conscious level and the combination of hemiplegia and hemianopia with higher cerebral dysfunction. Hemiparesis uncomplicated by hemianopia or higher cerebral dysfunction predicted a return to functional independence. A discriminant function derived from this analysis can be used to calculate the likelihood of recovery to independent function for an individual patient following an acute stroke.

Use of a microcomputer for the definition of multivariate confidence regions in medical diagnosis based on clinical laboratory profiles

The use of multivariate confidence regions is proposed for the classification of clinical laboratory profiles into diagnostic classes. For this purpose, a multivariate confidence region is developed for each diagnostic class. Three methods (UNEQ, EQ, and SIMCA) are evaluated and compared with classical linear discriminant analysis. As an example, a small data set concerning the differentiation of the thyroid functional states on the basis of five laboratory tests is used. It is shown that related procedures can produce results of very different quality and that the multivariate region approach is attractive for the clinician's daily practice since the methods are easily implemented on a microcomputer.

Differential laboratory diagnosis of hypercalcemia

It is proposed that this review will adopt the following format: establishment of hypercalcemia. This demands a discussion of the problem of normal ranges, the usage of either total calcium or ionized calcium in making this decision and where total calcium is used whether adjustment of this value for serum protein concentration should be used and if so, the formulae which have been cited to perform this. Having established hypercalcemia why is it necessary to differentiate this? This will involve reviewing those clinical situations in which differentiation of hypercalcemia has been attempted and will include an attempt to produce an up to date indication of conditions in which hypercalcemia has been described. When hypercalcemia has been established the laboratory tests which have been further used to discriminate will be divided into single tests such as N- or C- terminal parathormone, 1,25- dihydroxycholecalciferol, cyclic AMP; the combination tests which have been used including phosphate clearance, chloride vs. bicarbonate etc. proceeding to those groups which have used discriminant function to help in the decision making; dynamic testing will also be discussed particularly with reference to steroid suppression but will also include other known suppressants such as Mithramycin and Calcitonin. A final section will be included attempting to assess overall the present state of art in differentiating laboratory diagnosis of hypercalcemia and will also attempt to highlight those areas which appear to be most fruitful areas of progress in the future.

A morphometric study on the ultrastructure of well-differentiated tumours and inflammatory mucosa of the human urinary bladder

Transmission (TEM) and scanning electron microscopic (SEM) observations were performed on well-differentiated tumours and chronic cystitis in the human urinary bladder. SEM showed that the pleomorphic microvilli were present not only on the luminal surface of the tumour but also on the surface of inflammatory mucosa. The ultrastructure of six tumours and 5 cases of chronic cystitis was evaluated morphometrically. Bladder tumour and inflammatory mucosa were divided into several layers, namely outermost cells (S), subsurface cells just beneath these (S1), subsurface cells of 2 or 3 layers below (S23), intermediate cells of 2 or 3 layers above the basal cells (I23), intermediate cells just above the basal cells (I1) and basal cells (Ba). Areas of nucleus, cytoplasm and cytoplasmic organelles, numbers of nucleoli, nuclear bodies, mitochondria and lysosomes together with irregularity of the cell and nucleus were estimated according to the methods of Weibel. A multivariate analysis of variance on these variables showed that the above subdivision of layers was necessary for the comparison of tumour and inflammation. Discriminant analysis showed various differences between tumour and inflammatory mucosa. The results indicated that the Ba layer is the most effective site for differentiating the tumour from inflammation. Ba cells with large and irregular cytoplasm with an enlarged Golgi area, accompanied by many vacuolar structures, may be indicative of tumour rather than inflammation.

Morbidity in Adult Parathyroid Surgery

The results of surgery in a series of 700 consecutive cases of primary and tertiary hyperparathyroidism are reported with especial reference to mortality and morbidity. Providing that the operation is a first or second operation and that the patient is below 70 years of age, the operation has been found to be safe and uncomplicated.

On the transportability of linear discriminant functions

Different methods can give different results for the same analyte, and inconsistent answers may be obtained if such results are used in linear discriminant functions. This is an important factor to consider when transporting linear discriminant functions from one laboratory to another; the example of alkaline phosphatase activity and the differential diagnosis of hypercalcaemia has recently been given. This study shows that results obtained by the method recommended by the Scandinavian Committee on Enzymes for alkaline phosphatase may be used in the calculation of the discriminant functions used for the differential diagnosis of hypercalcaemia and considers other factors that may affect the discrimination. It is concluded that, with care, linear discriminant functions may be transported from one laboratory to another.

Biochemical and haematological indicators of excessive alcohol consumption

Discriminant function analysis was used to determine the optimum combination of haematological and biochemical tests which gave the best discrimination between hospital patients with high and low alcohol intakes. We studied 265 patients with alcohol-related disease, 133 gastroenterology outpatients drinking less than 20 g of alcohol per day, and 104 patients with a variety of non-alcoholic liver disease. Values of mean cell volume (MCV), serum bilirubin, aspartate transaminase, serum alkaline phosphatase (AP) and gamma glutamyl transferase (gamma GT), serum albumin, serum globulin, and uric acid were determined in each patient. The best discrimination between the three groups of patients was provided by a combination of mean corpuscular volume, log10 gamma GT, and log10 serum alkaline phosphatase. In women, 92% of the high alcohol group, 100% of the low alcohol group, and 87% of the non-alcoholic liver disease were correctly allocated by the discriminant analysis. The corresponding figures for the men were 80%, 100%, and 71%. Thus, over 80% of patients with excessive alcohol intake were correctly allocated by the use of three simple laboratory tests.

Jejunal mucosal morphometry in children with and without gut symptoms and in normal adults

Nineteen diagnostic peroral biopsy specimens from 18 children without diarrhoea, vomiting, or abdominal pain ('control' children) were compared with those taken from 23 children with diarrhoea of varying aetiology to establish the morphometric characteristics of jejunal mucosa in childhood. Comparison was also made with normal jejunal mucosa from adults. Statistical analysis of each characteristic individually showed no significant difference between the 'control' children and those with diarrhoea, but there were significant differences between the mucosae of 'control' children and those of adults; the villi tended to be shorter and the crypts longer in children. Thirty-seven per cent of specimens from the 'control' children showed a partial villous atrophy, that is, they were abnormal by adult criteria. Discriminant analysis of the features measured showed effective separation of the following groups: normal histology from partial villous atrophy in children, healthy adults from 'control' children, and normal histology in adults from normal histology in children.

Ectopic parathyroid adenomas

Two cases of parathyroid tumours occurring in unusual situations are described. Such cases may cause difficulty in both the diagnosis and the surgical treatment of hyperparathyroidism. The cases described illustrate the importance of a definitive aetiological diagnosis in hypercalcaemia, if appropriate surgery is to be performed. The value of discriminant function analysis and hydrocortisone suppression tests are discussed.

Hydrocortisone suppression test and discriminant analysis in differential diagnosis of hypercalcaemia

Experience is reported of the hydrocortisone suppression test in 140 hypercalcaemic patients, comprising 98 new cases of hyperparathyroidism and 42 cases of non-parathyroid malignant disease. The diagnostic accuracy of the test was compared in 168 patients with that of discriminant analysis, the discriminant functions being derived from plasma inorganic phosphate, alkaline phosphatase, chloride, bicarbonate, and urea, and the erythrocyte sedimentation rate. The hydrocortisone test and discriminant analysis each achieved a diagnostic accuracy of about 93% in 148 patients with either non-parathyroid malignant disease or hyperparathyroidism without osteitis fibrosa. When both tests pointed to the same diagnosis, they were wrong in less than 1% of cases. The hydrocortisone test was not helpful in patients with osteitis fibrosa. Both tests can be performed in any hospital with reliable standard laboratory services. Used in combination they have a high predictive value in distinguishing hypercalcaemia of parathyroid origin from that due to non-parathyroid malignant disease and have not led to errors of clinical importance. They should continue to play a major role in the differential diagnosis of hypercalcaemia until a prompt and reliable service finally establishes parathyroid hormone assay as the definitive laboratory procedure.

Computer-aided medical diagnosis: literature review

The difficulty of the medical diagnostic task and the advantages of the computer as an aid in this task are discussed. The general strategy and structure of any computer-aided system is presented, and the relationship of diagnostic accuracy to key variables involved in the development, test and use of a computer-aided diagnostic system is examined. These variables include: the computer algorithm, the source of the information used to develop the data base, the number and type of diseases under investigation, the number and type of indicants used, the source of the test sample, and the source of the validated diagnosis. A table of 58 empirically tested computer-aided medical diagnostic systems is presented; each system is summarised in relation to the variables mentioned above and diagnostic accuracy.

Discriminant analysis in the differential diagnosis of hypercalcaemia

Linear discriminant analysis, a multivariate statistical procedure, applied to serum calcium, phosphate, alkaline phosphatase, bicarbonate, chloride, creatinine and tubular reabsorption of phosphate, proved to be effective in distinguishing patients with Primary Hyperparathyroidism from other hypercalcaemic patients in eithy-four retrospective cases. The application of the model to thirty-four prospective cases enabled us to separate correctly, hyperparathyroid patients from non-parathyroid hypercalcaemic patients.

Further experience with discriminant functions in differential diagnosis of hypercalcaemia

Further experience has been obtained in the use of discriminant functions in the differential diagnosis of hypercalcaemia from the study of 140 new patients. The discriminant functions described in an earlier paper were derived from the results for plasma inorganic phosphate, alkaline phosphatase, chloride, bicarbonate and urea obtained from hypercalcaemic patients on admission to hospital. They indicated the correct diagnosis in ninety-two of 103 new hypercalcaemic patients (89·3%) admitted to University College Hospital and in thirty-one of thirty-seven hypercalcaemic patients at two other hospitals.

Revised discriminant functions have been calculated including the erythrocyte sedimentation rate as a sixth variable. These revised functions have led to some improvement in diagnostic accuracy. The correct diagnosis was indicated in ninety-three of ninety-eight patients (94·9%) at University College Hospital and in thirty-three of the thirty-seven patients at the two other hospitals.

Hypercalcemia in small cell (oat cell) carcinoma of the lung. Coincident parathyroid adenoma in one case

Hypercalcemia is very uncommon in small cell (oat cell) carcinoma of the lung. Two cases of this neoplasm associated with symptomatic hypercalcemia are described. Despite normal skeletal roentgenograms, metastatic bone disease was demonstrated by abnormal bone scans and bone biopsies in both patients. The combination of conventional antihypercalcemia therapy, cytotoxic cancer chemotherapy, and synthetic salmon calcitonin corrected the hypercalcemia despite progression of the small cell carcinoma. One patient with elevated serum immunoreactive parathyroid hormone (PTH) had a parathyroid adenoma at autopsy. This association emphasizes that in cases of bronchogenic small cell carcinoma with hypercalcemia, conincidental primary hyperparathyroidism should be considered.

Differential diagnosis of hypercalcemia by the chloride/phosphate ratio

The serum chloride and phosphate levels were measured and the chloride/phosphate ratios calculated in a group of eighty-four hypercalcemic patients. Although patients with hyperparathyroidism frequently had phosphate levels in the low normal range (less than 3 mg/100 ml) and chloride levels in the nigh normal range (greater than 102 mEq/L), they were nevertheless significantly different from the groups of patients with nonparathyroid hypercalcemia in whom phosphate levels were usually higher (greater than 3 mg/100 ml) and chloride levels usually lower (less than 102 mEq/L). The chloride/phosphate ratio was higher than 33 in 94 per cent of hyperparathyroid patients and lower than 33 in 96 per cent of other hypercalcemic patients. Thus, the measurements of serum phosphate and chloride levels and the calculation of the chloride/phosphate ratios were useful diagnostic screening tests that discriminated between patients with hypercalcemia of parathyroid and nonparathyroid origin with an accuracy of 95 per cent.

Effects of extracellular fluid volume contraction and expansion on the bicarbonaturia of parathyroid hormone

To evaluate the effect of extracellular fluid volume alterations on the bicarbonaturia of parathyroid hormone, thyroparathyroidectomized dogs were made alkalotic and volume-contracted or expanded through hemodialysis. Clearance studies were performed before and after infusion of purified bovine parathyroid extract (PTE). Glomerular filtration rate and blood bicarbonate concentrations were kept constant throughout the experiments. A significant increase in fractional bicarbonate excretion was observed following PTE infusion in both the volume-contracted (8.67 +/- 3.25 to 14.70 +/- 3.63%, P less than 0.010) and the volume-expanded state (22.80 +/- 3.04 to 37.26 +/- 3.38%, P less than 0.050). It is concluded that PTE decreases reabsorption of bicarbonate independent of the volume state of the animal.

Diagnosis and diagnostic patterns

A multivariate statistical analysis of biochemical data from patients with hypercalcaemia is presented as an example of the use of the computer as an aid to diagnosis.