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Onychomycosis (fungal nail infection) has come to public attention with the availability of effective oral therapy. The natural history and etiologic agents of this disease are discussed. The currently available methods of laboratory diagnosis are compared and contrasted.
Suspecting and diagnosing venous thrombosis and pulmonary embolism remain major clinical problems. For a variety of reasons, including the patient's pre-existing cardiac and pulmonary status and the release of humoral mediators, pulmonary emboli evoke varied responses in different patients. Symptoms and signs of pulmonary embolism are not specific; they depend on the size and the hemodynamic and humoral consequences of the embolus. Conversely, they may not be present at all. Chest radiographic and electrocardiographic findings are nonspecific, and may be most helpful in establishing the presence of other conditions that may be confused with pulmonary embolism. Arterial blood gases can only heighten the suspicion of pulmonary embolism; they should never be used to exclude the diagnosis. Clinical and laboratory findings therefore do not diagnose pulmonary embolism; rather, they raise the level of concern and set the stage for the performance of subsequent diagnostic studies.
Clinical diagnosis of invasive fungal infections demands a high clinical acumen, but both under- and over-diagnosis are common. Laboratory mycological tests have traditionally been limited by a range of complications. Development of methodologies to detect fungal-specific immunoglobulins, cell wall antigens and nucleic acid have improved dramatically in recent years.
The resurgence of tuberculosis and the increasing prevalence of multiple-resistant Mycobacterium tuberculosis strains are the reasons for the need of a rapid diagnosis of this infection. The article provides information about traditional and new methods in the laboratory diagnosis of tuberculosis, comparing their efficacy and rapidity.
This study describes a diagnostic pitfall in the laboratory diagnosis of patients with sphingomyelinase deficiency (SMD; Niemann-Pick disease types A and B; NPA and NPB), in cases where sphingomyelinase activity was not determined with sphingomyelin as the natural enzymic substrate. Four of 24 SMD patients studied had falsely normal or enhanced activity, when a so-called artificial sphingomyelinase substrate, 2-N-(hexadecanoyl)-amino-4-nitrophenyl phosphorylcholine (HNP), was used, whereas SMD was clear with the sphingomyelin substrate. Those four patients had the Q292 K mutation of the acid sphingomyelinase gene (SMPD1) on at least one allele. Three of the four patients (no data available from one) experienced only late-infantile or juvenile, though distinct, neurological involvement, where learning disabilities, hypo- or areflexia or mild ataxia were initial signs. The laboratory pitfall with HNP substrate, which is used in many laboratories, raises the risk that some SMD patients are overlooked, and it prevents the consideration of a late-manifesting neurological course in some patients as well as the planning of enzyme substitution therapy in non-neurological SMD (NPB) patients. Since classical NPB is very rare, it is suggested that SMD patients with late- or mild-manifesting neurological symptoms should better be assigned to additional SMD subgroups than grouped with NPB.
Invasive candidiasis is associated with high morbidity and mortality. Clinical diagnosis is complicated by a lack of specific clinical signs and symptoms of disease. Laboratory diagnosis is also complex because circulating antibodies to Candida species may occur in normal individuals as the result of commensal colonization of mucosal surfaces thereby reducing the usefulness of antibody detection for the diagnosis of this disease. In addition, Candida species antigens are often rapidly cleared from the circulation so that antigen detection tests often lack the desired level of sensitivity. Microbiological confirmation is difficult because blood cultures can be negative in up to 50% of autopsy-proven cases of deep-seated candidiasis or may only become positive late in the infection. Positive cultures from urine or mucosal surfaces do not necessarily indicate invasive disease although can occur during systemic infection. Furthermore, differences in the virulence and in the susceptibility of the various Candida species to antifungal drugs make identification to the species level important for clinical management. Newer molecular biological tests have generated interest but are not yet standardized or readily available in most clinical laboratory settings nor have they been validated in large clinical trials. Laboratory surveillance of at-risk patients could result in earlier initiation of antifungal therapy if sensitive and specific diagnostic tests, which are also cost effective, become available. This review will compare diagnostic tests currently in use as well as those under development by describing their assets and limitations for the diagnosis of invasive candidiasis.
The Oricult-N semiquantitative dipslide (Orion Diagnostica, Espoo, Finland) was evaluated for the laboratory diagnosis of vaginal candidiasis. It was compared with broth culture (Vagicult; Orion Diagnostica). Oricult-N was positive for 14.5% of 124 symptomatic patients and 12% of 50 asymptomatic controls. The results for broth cultures were 17 and 22%, respectively. Thus, the test group and the control group did not differ significantly by either method. High vaginal yeast counts (>/=10(5) CFU/ml) were detected by Oricult-N in 7% of patients and in 0% of controls, but both groups harbored low numbers of yeasts. An accurate quantitative cutoff point separating a level of yeast associated with infection from vaginal yeast carriage could not be defined in the study. Nevertheless, the easy semiquantitation allowed by the Oricult-N method could be helpful because, especially in low-count carriers of Candida, other potential causes of vaginal symptoms should be considered. The Oricult-N method was technically simple and could be applied in primary health care. Further studies are required, however, before Oricult-N can be recommended as a routine diagnostic tool.
The emergence of new viral infections of man requires the development of robust diagnostic tests that can be applied in the differential diagnosis of acute illness, or to determine past exposure, so as to establish the true burden of disease. Since the recognition in April 2003 of the severe acute respiratory syndrome coronavirus (SARS-CoV) as the causative agent of severe acute respiratory syndrome (SARS), enormous efforts have been applied to develop molecular and serological tests for SARS which can assist rapid detection of cases, accurate diagnosis of illness and the application of control measures. International progress in the laboratory diagnosis of SARS-CoV infection during acute illness has led to internationally agreed World Health Organization criteria for the confirmation of SARS. Developments in the dissection of the human immune response to SARS indicate that serological tests on convalescent sera are essential to confirm SARS infection, given the sub-optimal predictive value of molecular detection tests performed during acute SARS illness.
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The biochemical findings in 29 patients with Sanfilippo disease are reported and a scheme for laboratory diagnosis is outlined. A grossly elevated urinary excretion of heparan sulphate was a consistent and diagnostic finding, even at birth. The excretion of heparan sulphate and chondroitin sulphate was quantitatively similar in types A and B of the condition. Modifications of previously described methods for the determination of heparin sulphamidase in leucocytes or skin fibroblasts and N-acetyl-alpha-D-glucosaminidase in plasma or fibroblasts facilitated the measurement of specific activities. Sanfilippo A disease appeared to be the commonest mucopolysaccharidosis occurring in England and Sanfilippo B disease, one of the rarest forms.
The relative discriminatory value of the estimation of the serum reverse-T3 levels for the laboratory diagnosis of hyperthyroidism was investigated in 47 patients with clinical signs or symptoms of hyperthyroidism. The results were compared with those from the determination of the total serum levels of T3 and T4 prior and after correction for the binding proteins. Twenty-three of the patients had normal thyroid function and 24 had hyperthyroidism. The estimation of the total serum T3 level was superior to both the determination of the total serum T4 and reverse-T3 levels even subsequent to correction for the binding proteins.
The results obtained in the laboratory diagnosis of 609 cases of acute or subacute encephalitis, studied during a period of time of even years, is briefly presented. Diagnostic methods included virus isolation from stools and cerebrospinal fluid (CSF); specific serology in serum; detection of intrathecal production of IgG antibody; and, in the last two years, detection of viral genome sequences in CSF by the polymerase chain reaction. Significant results were obtained in 196 cases (32.2%) and the alfa-herpesviruses were responsible for a major part of them (77.5%). Furthermore, 18 cases were likely to respond to dual infection by both herpes simplex and varicella-zoster viruses. Epstein-Barr virus and Human herpesvirus 6 were found in CSF from three immunocompetent patients. Besides the current vaccination program, measles virus is still responsible for an important part (22/196, 11.2%) of cases of viral encephalitis.
The review emphasizes the significance of laboratory methods for the diagnosis of hog cholera virus. In addition to virus isolation and immunofluorescent method, enzyme immunoassay (EIA) of virus-specific antigen and antibodies are recommended. Commercial EIA kits for laboratory diagnosis of hog cholera virus and test-systems whose development is in progress now are characterized.
In the article that follows, Carroll and Reimer address a number of issues related to the clinical and laboratory diagnosis of upper respiratory tract infections. These syndromes occur with great frequency in both adults and children and have tremendous economic impact, related not only to lost productivity in the workplace but also to the frequent prescription by physicians of antibiotics, even when the etiologic agents of infection almost certainly are not bacteria. Most of these infections are diagnosed clinically, and specimens for microbiological identification are not obtained. Indeed, the difficulty in obtaining microbiological specimens that are not contaminated by resident colonizing flora often results in laboratory culture reports of dubious clinical value. As the authors note, the most standardized procedures are for the diagnosis of pharyngitis due to Streptococcus pyogenes. The preferred culture methods are reviewed as are the sensitivities, specificities, and limitations of rapid direct tests for group A streptococcal antigens. Currently, as the authors emphasize, a negative direct test mandates a conventional culture for S. pyogenes. More problematic are requests for isolation of other streptococci, Haemophilus species, corynebacteria, and gram-negative bacteria. Given limited resources, cost-containment imperatives, and the absence of clear evidence that these organisms are pharyngeal pathogens associated with important sequelae, my laboratory does not attempt to isolate these bacteria unless the ordering physician has directly consulted with me (the laboratory director). Carroll and Reimer emphasize that nasopharyngeal cultures have no place in the microbiological diagnosis of otitis media and that diagnostic tympanocentesis is the only procedure for obtaining specimens that yield reliable microbiological findings. They also point out the futility of using swabs to obtain material for the diagnosis of otitis externa, since the external auditory canal cannot be decontaminated sufficiently to obtain a meaningful culture result. Finally, the authors address the available methods for obtaining specimens to establish the etiology of sinusitis. For microbiological diagnosis, direct antral puncture has been the method of choice for many years. However, otorhinolaryngologists now obtain many specimens endoscopically. It probably is not possible to obtain specimens by this method without contamination by normal upper respiratory flora. Thus, results of cultures of endoscopic specimens are more difficult to interpret. For patients with complicated illnesses, use of the diagnostic "gold standard" of antral puncture, as well as biopsy with histopathologic correlation, should be encouraged.
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A bibliographical review is undertaken on dengue virus covering the period between 1952 and 1978 and including laboratory diagnosis aspects (viral isolation, serology, etc.), development of immunity and epidemiology.
All the above listed reasons as well as the experience we have obtained with this method, justify our recommendation of the introduction of the laboratory diagnosis of scabies through the method of lye scraping of the skin into routine practice. A single parasite element is enough for determining the diagnosis while, for the above mentioned reasons, a negative microscope finding does not exclude the parasitic etiology of the given disease. We therefore recommend in the diagnosis of scabies that the following criteria are parallely used: 1. an objective skin finding 2. laboratory proof of the causative agent of infestation 3. subjective feelings of the patient (itching at the typical time) 4. positive epidemiological anamnesis, primarily the occurrence of clinical symptoms in several members of a family or a group 5. diminishing of clinical symptoms after specific treatment with an anti-scabies medicament.